style: scanner not lexer

.golangci.yml

@@ -48,7 +48,7 @@ linters:
       # More information: https://golangci-lint.run/usage/false-positives/#comments
       #
       # Please uncomment the following line if your code is not using the godoc format
-      # - comments
+      - comments
 
       # Common false positives
       # feel free to remove this if you don't have any false positives
@@ -126,9 +126,6 @@ linters:
         # Blank import should be only in a main or test package, or have a comment justifying it.
         - name: blank-imports
 
-        # Packages should have comments of the form "Package x ...".
-        - name: package-comments
-
         # context.Context() should be the first parameter of a function when provided as argument.
         - name: context-as-argument
           arguments:
@@ -160,8 +157,6 @@ linters:
           arguments:
             # make error messages clearer
             - "sayRepetitiveInsteadOfStutters"
-            # require comments on public interface methods
-            - "checkPublicInterface"
 
         # incrementing an integer variable by 1 is recommended to be done using the `++` operator
         - name: increment-decrement

Makefile

@@ -1,53 +1,30 @@
 BINARY_NAME=lambda
-TEST=simple
 
-.PHONY: help build run profile explain graph docs test bench lint clean
+.PHONY: help build docs test bench clean
 .DEFAULT_GOAL := help
 .SILENT:
 
 help:
 	echo "Available targets:"
 	echo "  build    - Build the lambda executable"
-	echo "  run      - Build and run the lambda runtime (use TEST=<name> to specify sample)"
-	echo "  profile  - Build and run with CPU profiling enabled"
-	echo "  explain  - Build and run with explanation mode and profiling"
-	echo "  graph    - Generate and open CPU profile visualization"
 	echo "  docs     - Start local godoc server on port 6060"
-	echo "  test     - Run tests for all samples"
+	echo "  test     - Run tests"
-	echo "  bench    - Run benchmarks for all samples"
+	echo "  bench    - Run benchmarks"
-	echo "  lint     - Run golangci-lint on all packages"
 	echo "  clean    - Remove all build artifacts"
 
 build:
 	go build -o ${BINARY_NAME} ./cmd/lambda
 	chmod +x ${BINARY_NAME}
 
-run: build
-	./${BINARY_NAME} -s -f ./tests/$(TEST).test -o program.out
-
-profile: build
-	./${BINARY_NAME} -p profile/cpu.prof -f ./tests/$(TEST).test -o program.out
-
-explain: build
-	./${BINARY_NAME} -x -p profile/cpu.prof -f ./tests/$(TEST).test -o program.out > explain.out
-
-graph:
-	go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof
-	go tool pprof -svg profile/cpu.prof > profile/cpu.svg
-	echo ">>> View at 'file://$(PWD)/profile/cpu.svg'"
-
 docs:
 	echo ">>> View at 'http://localhost:6060/pkg/git.maximhutz.com/max/lambda/'"
 	go run golang.org/x/tools/cmd/godoc@latest -http=:6060
 
 test:
-	go test -v ./cmd/lambda
+	go test -v ./...
 
 bench:
-	go test -bench=. -benchtime=10x -cpu=4 ./cmd/lambda
+	go test -bench=. -benchtime=10x -cpu=4 ./...
-
-lint:
-	go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@latest run ./...
 
 clean:
 	rm -f ${BINARY_NAME}

cmd/lambda/convert.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var convertCmd = &cobra.Command{
+	Use:   "convert [input] [output]",
+	Short: "Convert between lambda calculus representations",
+	Long: `Convert lambda calculus expressions between different representations.
+
+The format is inferred from file extensions when possible.
+Use --from and --to flags to override format detection.`,
+	Example: `  lambda convert input.sch output.dbi
+  lambda convert input.txt output.txt --from saccharine --to lambda`,
+	Args: cobra.ExactArgs(2),
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	convertCmd.Flags().String("from", "", "source format")
+	convertCmd.Flags().String("to", "", "target format")
+	rootCmd.AddCommand(convertCmd)
+}

cmd/lambda/engine.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var engineCmd = &cobra.Command{
+	Use:   "engine",
+	Short: "List available evaluation engines",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(engineCmd)
+}

cmd/lambda/lambda.go

@@ -1,32 +0,0 @@
-// Package main defines the 'lambda' command-line interface (CLI).
-package main
-
-import (
-	"os"
-
-	"github.com/spf13/cobra"
-)
-
-func Lambda() *cobra.Command {
-	cmd := &cobra.Command{
-		Use:   "lambda",
-		Short: "Lambda calculus interpreter",
-		Long:  "A lambda calculus interpreter supporting multiple representations.",
-		RunE: func(cmd *cobra.Command, _ []string) error {
-			return cmd.Help()
-		},
-	}
-
-	cmd.AddCommand(LambdaConvert())
-	cmd.AddCommand(LambdaEngine())
-	cmd.AddCommand(LambdaReduce())
-
-	return cmd
-}
-
-func main() {
-	lambda := Lambda()
-	if err := lambda.Execute(); err != nil {
-		os.Exit(1)
-	}
-}

cmd/lambda/lambda_convert.go

@@ -1,95 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"os"
-	"path/filepath"
-	"strings"
-
-	"github.com/spf13/cobra"
-)
-
-// inferReprFromPath returns the repr type based on file extension.
-func inferReprFromPath(path string) (string, error) {
-	switch ext := strings.ToLower(filepath.Ext(path)); ext {
-	case ".lambda", ".lam", ".lc":
-		return "lambda", nil
-	case ".saccharine", ".sch":
-		return "saccharine", nil
-	default:
-		return "", fmt.Errorf("unknown file extension '%s'", ext)
-	}
-}
-
-func LambdaConvert() *cobra.Command {
-	var inputReprFlag, outputReprFlag string
-
-	cmd := &cobra.Command{
-		Use:          "convert <input-file> <output-file>",
-		Aliases:      []string{"conv"},
-		Short:        "Convert between lambda calculus representations",
-		SilenceUsage: true,
-		RunE: func(cmd *cobra.Command, args []string) error {
-			if len(args) != 2 {
-				return cmd.Help()
-			}
-
-			var err error
-			inputPath, outputPath := args[0], args[1]
-
-			// Use flag if provided, otherwise infer from extension.
-			inputRepr := inputReprFlag
-			if inputRepr == "" {
-				if inputRepr, err = inferReprFromPath(inputPath); err != nil {
-					return fmt.Errorf("input file: %w", err)
-				}
-			}
-
-			outputRepr := outputReprFlag
-			if outputRepr == "" {
-				if outputRepr, err = inferReprFromPath(outputPath); err != nil {
-					return fmt.Errorf("output file: %w", err)
-				}
-			}
-
-			// Read input file.
-			input, err := os.ReadFile(inputPath)
-			if err != nil {
-				return fmt.Errorf("reading input file: %w", err)
-			}
-
-			r := GetRegistry()
-
-			// Parse input into syntax tree.
-			repr, err := r.Unmarshal(string(input), inputRepr)
-			if err != nil {
-				return fmt.Errorf("parsing input: %w", err)
-			}
-
-			// Convert to output repr if different.
-			result, err := r.ConvertTo(repr, outputRepr)
-			if err != nil {
-				return fmt.Errorf("converting %s to %s: %w", inputRepr, outputRepr, err)
-			}
-
-			// Marshal output.
-			output, err := r.Marshal(result)
-			if err != nil {
-				return fmt.Errorf("unmarshaling output: %w", err)
-			}
-
-			// Write output file.
-			err = os.WriteFile(outputPath, []byte(output), 0644)
-			if err != nil {
-				return fmt.Errorf("writing output file: %w", err)
-			}
-
-			return nil
-		},
-	}
-
-	cmd.Flags().StringVarP(&inputReprFlag, "input", "i", "", "Input representation (inferred from extension if unset)")
-	cmd.Flags().StringVarP(&outputReprFlag, "output", "o", "", "Output representation (inferred from extension if unset)")
-
-	return cmd
-}

cmd/lambda/lambda_engine.go

@@ -1,20 +0,0 @@
-package main
-
-import (
-	"github.com/spf13/cobra"
-)
-
-func LambdaEngine() *cobra.Command {
-	cmd := &cobra.Command{
-		Use:     "engine",
-		Aliases: []string{"eng"},
-		Short:   "Information about available engines",
-		RunE: func(cmd *cobra.Command, _ []string) error {
-			return cmd.Help()
-		},
-	}
-
-	cmd.AddCommand(LambdaEngineList())
-
-	return cmd
-}

cmd/lambda/lambda_engine_list.go

@@ -1,26 +0,0 @@
-package main
-
-import (
-	"fmt"
-
-	"github.com/spf13/cobra"
-)
-
-func LambdaEngineList() *cobra.Command {
-	cmd := &cobra.Command{
-		Use:     "list",
-		Aliases: []string{"ls"},
-		Short:   "List available engines",
-		RunE: func(*cobra.Command, []string) error {
-			r := GetRegistry()
-
-			for engine := range r.ListEngines() {
-				fmt.Println(engine.Name())
-			}
-
-			return nil
-		},
-	}
-
-	return cmd
-}

cmd/lambda/lambda_reduce.go

@@ -1,108 +0,0 @@
-package main
-
-import (
-	"fmt"
-
-	"github.com/spf13/cobra"
-
-	"git.maximhutz.com/max/lambda/internal/cli"
-	"git.maximhutz.com/max/lambda/internal/registry"
-)
-
-func LambdaReduce() *cobra.Command {
-	var inputReprFlag string
-	var engineFlag string
-
-	cmd := &cobra.Command{
-		Use:          "reduce <input-file>",
-		Short:        "Reduce a lambda calculus expression",
-		SilenceUsage: true,
-		Aliases:      []string{"run"},
-		RunE: func(cmd *cobra.Command, args []string) error {
-			var err error
-			if len(args) != 1 {
-				return cmd.Help()
-			}
-
-			inputPath := args[0]
-
-			// Get input source.
-			var source cli.Source
-			if inputPath == "-" {
-				source = cli.StdinSource{}
-			} else {
-				source = cli.FileSource{Path: inputPath}
-			}
-
-			destination := cli.StdoutDestination{}
-
-			r := GetRegistry()
-
-			// Get input.
-			input, err := source.Extract()
-			if err != nil {
-				return err
-			}
-
-			// Use flag if provided, otherwise infer from extension.
-			inputRepr := inputReprFlag
-			if inputRepr == "" {
-				if inputRepr, err = inferReprFromPath(inputPath); err != nil {
-					return fmt.Errorf("input file: %w", err)
-				}
-			}
-
-			// Find engine.
-			var engine registry.Engine
-			if engineFlag == "" {
-				if engine, err = r.GetDefaultEngine(inputRepr); err != nil {
-					return err
-				}
-			} else {
-				if engine, err = r.GetEngine(engineFlag); err != nil {
-					return err
-				}
-			}
-
-			// Parse code into syntax tree.
-			repr, err := r.Unmarshal(input, inputRepr)
-			if err != nil {
-				return err
-			}
-
-			// Compile expression to lambda calculus.
-			compiled, err := r.ConvertTo(repr, "lambda")
-			if err != nil {
-				return err
-			}
-
-			// Create process.
-			process, err := engine.Load(compiled)
-			if err != nil {
-				return err
-			}
-
-			// Run reduction.
-			for process.Step(1) {
-			}
-
-			// Return the final reduced result.
-			result, err := process.Get()
-			if err != nil {
-				return err
-			}
-
-			output, err := r.Marshal(result)
-			if err != nil {
-				return err
-			}
-
-			return destination.Write(output)
-		},
-	}
-
-	cmd.Flags().StringVarP(&inputReprFlag, "input", "i", "", "Input representation (inferred from extension if unset)")
-	cmd.Flags().StringVarP(&engineFlag, "engine", "e", "", "Reduction engine (inferred from '--input' if unset)")
-
-	return cmd
-}

cmd/lambda/registry.go

@@ -1,26 +0,0 @@
-package main
-
-import (
-	"git.maximhutz.com/max/lambda/internal/registry"
-	"git.maximhutz.com/max/lambda/pkg/convert"
-	"git.maximhutz.com/max/lambda/pkg/engine/normalorder"
-	"git.maximhutz.com/max/lambda/pkg/lambda"
-	"git.maximhutz.com/max/lambda/pkg/saccharine"
-)
-
-func GetRegistry() *registry.Registry {
-	r := registry.New()
-
-	// Codecs
-	(registry.RegisterConversion(r, convert.Saccharine2Lambda, "saccharine", "lambda"))
-	(registry.RegisterConversion(r, convert.Lambda2Saccharine, "lambda", "saccharine"))
-
-	// Engines
-	(registry.RegisterEngine(r, normalorder.NewProcess, "normalorder", "lambda"))
-
-	// Marshalers
-	(registry.RegisterCodec(r, lambda.Codec{}, "lambda"))
-	(registry.RegisterCodec(r, saccharine.Codec{}, "saccharine"))
-
-	return r
-}

cmd/lambda/repl.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var replCmd = &cobra.Command{
+	Use:   "repl",
+	Short: "Start an interactive lambda calculus REPL",
+	Long: `Start an interactive Read-Eval-Print Loop for lambda calculus.
+
+Enter lambda expressions to evaluate them.
+Type 'exit' or 'quit' to leave the REPL.
+Press Ctrl+D to exit.`,
+	Example: `  lambda repl`,
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(replCmd)
+}

cmd/lambda/repr.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var reprCmd = &cobra.Command{
+	Use:   "repr",
+	Short: "List available representations",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(reprCmd)
+}

cmd/lambda/root.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "lambda",
+	Short: "A lambda calculus interpreter and toolkit",
+	Long:  `Lambda is a CLI tool for working with lambda calculus expressions.`,
+}
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		os.Exit(1)
+	}
+}

cmd/lambda/run.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var runCmd = &cobra.Command{
+	Use:   "run [expression]",
+	Short: "Evaluate a lambda calculus expression",
+	Long: `Evaluate a lambda calculus expression and print the result.
+
+The expression can be provided as an argument, read from a file with --file,
+or piped through stdin.`,
+	Example: `  lambda run "\x.x"
+  echo "\x.x" | lambda run
+  lambda run --file program.sch
+  lambda run --file program.sch --engine krivine`,
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	runCmd.Flags().StringP("file", "f", "", "read expression from file")
+	runCmd.Flags().StringP("engine", "e", "normal", "evaluation engine to use")
+	rootCmd.AddCommand(runCmd)
+}

cmd/lambda/trace.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var traceCmd = &cobra.Command{
+	Use:   "trace [file]",
+	Short: "Trace the evaluation of a lambda calculus expression",
+	Long: `Trace the step-by-step evaluation of a lambda calculus expression.
+
+This command shows each reduction step during evaluation.`,
+	Example: `  lambda trace program.sch
+  lambda trace program.sch --engine krivine`,
+	Args: cobra.ExactArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Fprintln(os.Stderr, "not implemented")
+		os.Exit(1)
+	},
+}
+
+func init() {
+	traceCmd.Flags().StringP("engine", "e", "normal", "evaluation engine to use")
+	rootCmd.AddCommand(traceCmd)
+}

go.mod

@@ -2,9 +2,13 @@ module git.maximhutz.com/max/lambda
 
 go 1.25.5
 
-require github.com/spf13/cobra v1.10.2
+require github.com/stretchr/testify v1.11.1
 
 require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
-	github.com/spf13/pflag v1.0.10 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,11 +1,18 @@
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
 github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
-github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
-github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/cli/cli.go

@@ -1,2 +0,0 @@
-// Package cli package provides various utilities to the 'lambda' program.
-package cli

internal/cli/destination.go

@@ -1,29 +0,0 @@
-package cli
-
-import (
-	"fmt"
-	"os"
-)
-
-// A Destination is method of writing output to the user.
-type Destination interface {
-	// Write data to this destination.
-	Write(data string) error
-}
-
-// An StdoutDestination writes to stdout.
-type StdoutDestination struct{}
-
-// Write outputs to standard output.
-func (d StdoutDestination) Write(data string) error {
-	fmt.Println(data)
-	return nil
-}
-
-// A FileDestination writes to a file.
-type FileDestination struct{ Path string }
-
-// Write outputs to a file.
-func (d FileDestination) Write(data string) error {
-	return os.WriteFile(d.Path, []byte(data+"\n"), 0644)
-}

internal/cli/source.go

@@ -1,44 +0,0 @@
-package cli
-
-import (
-	"io"
-	"os"
-)
-
-// A Source is a method of extracting input from the user.
-type Source interface {
-	// Extract fetches data from this source.
-	Extract() (string, error)
-}
-
-// A StringSource is defined by a string.
-type StringSource struct{ Data string }
-
-// Extract pulls input data from the internal string.
-func (s StringSource) Extract() (string, error) { return s.Data, nil }
-
-// A StdinSource pulls from standard input.
-type StdinSource struct{}
-
-// Extract pulls input data from standard input.
-func (s StdinSource) Extract() (string, error) {
-	data, err := io.ReadAll(os.Stdin)
-	if err != nil {
-		return "", err
-	}
-
-	return string(data), nil
-}
-
-// A FileSource reads from a file.
-type FileSource struct{ Path string }
-
-// Extract pulls input data from the file source.
-func (s FileSource) Extract() (string, error) {
-	data, err := os.ReadFile(s.Path)
-	if err != nil {
-		return "", err
-	}
-
-	return string(data), nil
-}

internal/registry/codec.go

@@ -1,58 +0,0 @@
-package registry
-
-import (
-	"fmt"
-	"reflect"
-
-	"git.maximhutz.com/max/lambda/pkg/codec"
-)
-
-// A Codec is a type-erased codec that serializes and deserializes expressions
-// as Expr values, regardless of the underlying representation type.
-type Codec interface {
-	codec.Codec[Expr]
-
-	// InType returns the name of the representation this codec handles.
-	InType() string
-}
-
-// A registeredCodec adapts a typed codec.Codec[T] into the type-erased Codec
-// interface. It wraps decoded values into Expr on decode, and extracts the
-// underlying T from an Expr on encode.
-type registeredCodec[T any] struct {
-	codec  codec.Codec[T]
-	inType string
-}
-
-func (c registeredCodec[T]) Decode(s string) (Expr, error) {
-	t, err := c.codec.Decode(s)
-	if err != nil {
-		return nil, err
-	}
-
-	return NewExpr(c.inType, t), nil
-}
-
-func (c registeredCodec[T]) Encode(r Expr) (string, error) {
-	t, ok := r.Data().(T)
-	if !ok {
-		dataType := reflect.TypeOf(r.Data())
-		allowedType := reflect.TypeFor[T]()
-		return "", fmt.Errorf("Codec for '%s' cannot parse '%s'", allowedType, dataType)
-	}
-
-	return c.codec.Encode(t)
-}
-
-func (c registeredCodec[T]) InType() string { return c.inType }
-
-// RegisterCodec registers a typed codec under the given representation name.
-// Returns an error if a codec for that representation is already registered.
-func RegisterCodec[T any](registry *Registry, m codec.Codec[T], inType string) error {
-	if _, ok := registry.codecs[inType]; ok {
-		return fmt.Errorf("Codec for '%s' already registered", inType)
-	}
-
-	registry.codecs[inType] = registeredCodec[T]{m, inType}
-	return nil
-}

internal/registry/conversion.go

@@ -1,59 +0,0 @@
-package registry
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/codec"
-)
-
-// A Conversion is a type-erased transformation from one representation to
-// another. It operates on Expr values, hiding the underlying representation
-// types.
-type Conversion interface {
-	// InType returns the name of the source representation.
-	InType() string
-	// OutType returns the name of the target representation.
-	OutType() string
-
-	// Run applies the conversion to the given expression. Returns an error if
-	// the expression's data does not match the expected source type.
-	Run(Expr) (Expr, error)
-}
-
-// A registeredConversion adapts a typed codec.Conversion[T, U] into the
-// type-erased Conversion interface. It extracts the underlying T from an Expr,
-// applies the conversion, and wraps the result as a new Expr.
-type registeredConversion[T, U any] struct {
-	conversion      codec.Conversion[T, U]
-	inType, outType string
-}
-
-func (c registeredConversion[T, U]) Run(expr Expr) (Expr, error) {
-	t, ok := expr.Data().(T)
-	if !ok {
-		return nil, fmt.Errorf("could not parse '%v' as '%s'", t, c.inType)
-	}
-
-	u, err := c.conversion(t)
-	if err != nil {
-		return nil, err
-	}
-
-	return NewExpr(c.outType, u), nil
-}
-
-func (c registeredConversion[T, U]) InType() string { return c.inType }
-
-func (c registeredConversion[T, U]) OutType() string { return c.outType }
-
-// RegisterConversion registers a typed conversion function between two
-// representations.
-func RegisterConversion[T, U any](
-	registry *Registry,
-	conversion codec.Conversion[T, U],
-	inType, outType string,
-) error {
-	registry.converter.Add(registeredConversion[T, U]{conversion, inType, outType})
-
-	return nil
-}

internal/registry/converter.go

@@ -1,30 +0,0 @@
-package registry
-
-// A Converter is a directed graph of conversions between representations. Each
-// node is a representation name, and each edge is a Conversion.
-type Converter struct {
-	data map[string][]Conversion
-}
-
-// NewConverter creates an empty Converter with no registered conversions.
-func NewConverter() *Converter {
-	return &Converter{data: map[string][]Conversion{}}
-}
-
-// Add registers a conversion, adding an edge from its source representation
-// to its target representation.
-func (g *Converter) Add(c Conversion) {
-	conversionsFromIn, ok := g.data[c.InType()]
-	if !ok {
-		conversionsFromIn = []Conversion{}
-	}
-
-	conversionsFromIn = append(conversionsFromIn, c)
-	g.data[c.InType()] = conversionsFromIn
-}
-
-// ConversionsFrom returns all conversions that have the given representation
-// as their source type.
-func (g *Converter) ConversionsFrom(t string) []Conversion {
-	return g.data[t]
-}

internal/registry/engine.go

@@ -1,58 +0,0 @@
-package registry
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/engine"
-)
-
-// An Engine is a type-erased evaluation engine that can load an expression
-// into a runnable Process.
-type Engine interface {
-	// Load prepares an expression for evaluation, returning a Process. Returns
-	// an error if the expression's data does not match the engine's expected
-	// representation type.
-	Load(Expr) (Process, error)
-	// Name returns the name of this engine.
-	Name() string
-	// InType returns the name of the representation this engine operates on.
-	InType() string
-}
-
-// A registeredEngine adapts a typed engine.Engine[T] into the type-erased
-// Engine interface. It extracts the underlying T from an Expr before passing it
-// to the engine.
-type registeredEngine[T any] struct {
-	engine engine.Engine[T]
-	name   string
-	inType string
-}
-
-func (e registeredEngine[T]) InType() string { return e.inType }
-
-func (e registeredEngine[T]) Name() string { return e.name }
-
-func (e registeredEngine[T]) Load(expr Expr) (Process, error) {
-	t, ok := expr.Data().(T)
-	if !ok {
-		return nil, fmt.Errorf("incorrect format '%s' for engine '%s'", expr.Repr(), e.inType)
-	}
-
-	process, err := e.engine(t)
-	if err != nil {
-		return nil, err
-	}
-
-	return registeredProcess[T]{process, e.inType}, nil
-}
-
-// RegisterEngine registers a typed engine under the given name. Returns an
-// error if an engine with that name is already registered.
-func RegisterEngine[T any](registry *Registry, e engine.Engine[T], name, inType string) error {
-	if _, ok := registry.engines[name]; ok {
-		return fmt.Errorf("engine '%s' already registered", name)
-	}
-
-	registry.engines[name] = &registeredEngine[T]{e, name, inType}
-	return nil
-}

internal/registry/expr.go

@@ -1,26 +0,0 @@
-package registry
-
-// An Expr is a type-erased lambda calculus expression. It can have any type of
-// representation, so long as that type is known to the registry it is handled
-// by.
-type Expr interface {
-	// Repr returns the name of the underlying representation. Two expressions
-	// with the same Repr() are assumed to have the same representation type.
-	Repr() string
-
-	// Data returns the underlying expression data.
-	Data() any
-}
-
-// A baseExpr is the default implementation of Expr.
-type baseExpr struct {
-	id   string
-	data any
-}
-
-func (e baseExpr) Repr() string { return e.id }
-
-func (e baseExpr) Data() any { return e.data }
-
-// NewExpr creates an Expr with the given representation name and data.
-func NewExpr(id string, data any) Expr { return baseExpr{id, data} }

internal/registry/process.go

@@ -1,35 +0,0 @@
-package registry
-
-import (
-	"git.maximhutz.com/max/lambda/pkg/engine"
-)
-
-// A Process is a type-erased reduction process that operates on Expr values.
-type Process interface {
-	engine.Process[Expr]
-
-	// InType returns the name of the representation this process operates on.
-	InType() string
-}
-
-// A registeredProcess adapts a typed engine.Process[T] into the type-erased
-// Process interface. It wraps the result of Get into an Expr.
-type registeredProcess[T any] struct {
-	process engine.Process[T]
-	inType  string
-}
-
-func (p registeredProcess[T]) InType() string { return p.inType }
-
-func (p registeredProcess[T]) Get() (Expr, error) {
-	s, err := p.process.Get()
-	if err != nil {
-		return nil, err
-	}
-
-	return NewExpr(p.inType, s), nil
-}
-
-func (p registeredProcess[T]) Step(i int) bool {
-	return p.process.Step(i)
-}

internal/registry/registry.go

@@ -1,153 +0,0 @@
-// Package registry defines a structure to hold all available representations,
-// engines, and conversions between them.
-package registry
-
-import (
-	"fmt"
-	"iter"
-	"maps"
-)
-
-// A Registry holds all representations, conversions, codecs, and engines
-// available to the program.
-type Registry struct {
-	codecs    map[string]Codec
-	converter *Converter
-	engines   map[string]Engine
-}
-
-// New makes an empty registry.
-func New() *Registry {
-	return &Registry{
-		codecs:    map[string]Codec{},
-		converter: NewConverter(),
-		engines:   map[string]Engine{},
-	}
-}
-
-// GetEngine finds an engine based on its name. Returns an error if an engine
-// with that name cannot be found.
-func (r Registry) GetEngine(name string) (Engine, error) {
-	e, ok := r.engines[name]
-	if !ok {
-		return nil, fmt.Errorf("engine '%s' not found", name)
-	}
-
-	return e, nil
-}
-
-// ListEngines returns all available engines to the registry.
-func (r Registry) ListEngines() iter.Seq[Engine] {
-	return maps.Values(r.engines)
-}
-
-// GetDefaultEngine infers the preferred engine for a representation. Returns an
-// error if one cannot be chosen.
-func (r *Registry) GetDefaultEngine(id string) (Engine, error) {
-	for _, engine := range r.engines {
-		if engine.InType() == id {
-			return engine, nil
-		}
-	}
-
-	return r.GetEngine("normalorder")
-
-	// return nil, fmt.Errorf("no engine for '%s'", id)
-}
-
-// ConvertTo attempts to convert an expression of one type of representation to
-// another. Returns the converted expression, otherwise an error.
-//
-// It can convert between any two types of representations, given there is a
-// valid conversion path between them. It uses BFS to traverse a graph of
-// conversion edges, and converts along the shortest path.
-func (r *Registry) ConvertTo(expr Expr, outType string) (Expr, error) {
-	path, err := r.ConversionPath(expr.Repr(), outType)
-	if err != nil {
-		return nil, err
-	}
-
-	result := expr
-	for _, conversion := range path {
-		result, err = conversion.Run(result)
-		if err != nil {
-			return nil, fmt.Errorf("converting '%s' to '%s': %w", conversion.InType(), conversion.OutType(), err)
-		}
-	}
-
-	return result, err
-}
-
-// Marshal serializes an expression, given that representation has a codec.
-// Returns an error if the representation is not registered, or it has no codec.
-func (r *Registry) Marshal(expr Expr) (string, error) {
-	m, ok := r.codecs[expr.Repr()]
-	if !ok {
-		return "", fmt.Errorf("no marshaler for '%s'", expr.Repr())
-	}
-
-	return m.Encode(expr)
-}
-
-// Unmarshal deserializes an expression. Returns an error if the representation
-// or a codec for it is not registered.
-func (r *Registry) Unmarshal(s string, outType string) (Expr, error) {
-	m, ok := r.codecs[outType]
-	if !ok {
-		return nil, fmt.Errorf("no marshaler for '%s'", outType)
-	}
-
-	return m.Decode(s)
-}
-
-func reverse[T any](list []T) []T {
-	if list == nil {
-		return list
-	}
-
-	reversed := []T{}
-
-	for i := len(list) - 1; i >= 0; i-- {
-		reversed = append(reversed, list[i])
-	}
-
-	return reversed
-}
-
-// ConversionPath attempts to find a set of valid conversions that (if applied)
-// convert one representation to another. Returns an error if no path can be
-// found.
-func (r *Registry) ConversionPath(from, to string) ([]Conversion, error) {
-	backtrack := map[string]Conversion{}
-	iteration := []string{from}
-	for len(iteration) > 0 {
-		nextIteration := []string{}
-
-		for _, item := range iteration {
-			for _, conversion := range r.converter.ConversionsFrom(item) {
-				if _, ok := backtrack[conversion.OutType()]; ok {
-					continue
-				}
-
-				nextIteration = append(nextIteration, conversion.OutType())
-				backtrack[conversion.OutType()] = conversion
-			}
-		}
-
-		iteration = nextIteration
-	}
-
-	reversedPath := []Conversion{}
-	current := to
-	for current != from {
-		conversion, ok := backtrack[current]
-		if !ok {
-			return nil, fmt.Errorf("no valid conversion from '%s' to '%s'", from, to)
-		}
-
-		reversedPath = append(reversedPath, conversion)
-		current = conversion.InType()
-	}
-
-	return reverse(reversedPath), nil
-}

pkg/codec/codec.go

@@ -1,20 +0,0 @@
-// Package codec defines processes to convert between different representations
-// of lambda calculus, and serialize the different representations.
-package codec
-
-// A Conversion is a function that turns one representation into another.
-// Returns an error if the input expression cannot be converted.
-type Conversion[T, U any] = func(T) (U, error)
-
-// A Codec is an object that can serialize/deserialize one type of
-// representation. It is assumed that for any x ∋ T, Decode(Encode(x)) = x.
-type Codec[T any] interface {
-	// Encode takes an expression, and returns its serialized format, as a
-	// string. Returns an error if the expression cannot be serialized.
-	Encode(T) (string, error)
-
-	// Decode takes the serialized format of an expression, and returns its true
-	// value. Returns an error if the string doesn't correctly represent any
-	// valid expression.
-	Decode(string) (T, error)
-}

pkg/convert/saccharine_to_lambda.go

@@ -1,49 +1,47 @@
-// Package convert defined some standard conversions between various types of
-// representations.
 package convert
 
 import (
 	"fmt"
 
-	"git.maximhutz.com/max/lambda/pkg/lambda"
+	"git.maximhutz.com/max/lambda/pkg/repr/lambda"
-	"git.maximhutz.com/max/lambda/pkg/saccharine"
+	"git.maximhutz.com/max/lambda/pkg/repr/saccharine"
 )
 
-func encodeAtom(n *saccharine.Atom) lambda.Expression {
+func convertAtom(n *saccharine.Variable) lambda.Expression {
-	return lambda.Variable{Name: n.Name}
+	return lambda.NewVariable(n.Name)
 }
 
-func encodeAbstraction(n *saccharine.Abstraction) lambda.Expression {
+func convertAbstraction(n *saccharine.Abstraction) lambda.Expression {
-	result := encodeExpression(n.Body)
+	result := SaccharineToLambda(n.Body)
 
 	parameters := n.Parameters
 
 	// If the function has no parameters, it is a thunk. Lambda calculus still
 	// requires _some_ parameter exists, so generate one.
 	if len(parameters) == 0 {
-		freeVars := lambda.GetFree(result)
+		freeVars := result.GetFree()
 		freshName := lambda.GenerateFreshName(freeVars)
 		parameters = append(parameters, freshName)
 	}
 
 	for i := len(parameters) - 1; i >= 0; i-- {
-		result = lambda.Abstraction{Parameter: parameters[i], Body: result}
+		result = lambda.NewAbstraction(parameters[i], result)
 	}
 
 	return result
 }
 
-func encodeApplication(n *saccharine.Application) lambda.Expression {
+func convertApplication(n *saccharine.Application) lambda.Expression {
-	result := encodeExpression(n.Abstraction)
+	result := SaccharineToLambda(n.Abstraction)
 
 	arguments := []lambda.Expression{}
 	for _, argument := range n.Arguments {
-		encodeedArgument := encodeExpression(argument)
+		convertedArgument := SaccharineToLambda(argument)
-		arguments = append(arguments, encodeedArgument)
+		arguments = append(arguments, convertedArgument)
 	}
 
 	for _, argument := range arguments {
-		result = lambda.Application{Abstraction: result, Argument: argument}
+		result = lambda.NewApplication(result, argument)
 	}
 
 	return result
@@ -53,24 +51,24 @@ func reduceLet(s *saccharine.LetStatement, e lambda.Expression) lambda.Expressio
 	var value lambda.Expression
 
 	if len(s.Parameters) == 0 {
-		value = encodeExpression(s.Body)
+		value = SaccharineToLambda(s.Body)
 	} else {
-		value = encodeAbstraction(&saccharine.Abstraction{Parameters: s.Parameters, Body: s.Body})
+		value = convertAbstraction(saccharine.NewAbstraction(s.Parameters, s.Body))
 	}
 
-	return lambda.Application{
+	return lambda.NewApplication(
-		Abstraction: lambda.Abstraction{Parameter: s.Name, Body: e},
+		lambda.NewAbstraction(s.Name, e),
-		Argument:    value,
+		value,
-	}
+	)
 }
 
 func reduceDeclare(s *saccharine.DeclareStatement, e lambda.Expression) lambda.Expression {
-	freshVar := lambda.GenerateFreshName(lambda.GetFree(e))
+	freshVar := lambda.GenerateFreshName(e.GetFree())
 
-	return lambda.Application{
+	return lambda.NewApplication(
-		Abstraction: lambda.Abstraction{Parameter: freshVar, Body: e},
+		lambda.NewAbstraction(freshVar, e),
-		Argument:    encodeExpression(s.Value),
+		SaccharineToLambda(s.Value),
-	}
+	)
 }
 
 func reduceStatement(s saccharine.Statement, e lambda.Expression) lambda.Expression {
@@ -84,8 +82,8 @@ func reduceStatement(s saccharine.Statement, e lambda.Expression) lambda.Express
 	}
 }
 
-func encodeClause(n *saccharine.Clause) lambda.Expression {
+func convertClause(n *saccharine.Clause) lambda.Expression {
-	result := encodeExpression(n.Returns)
+	result := SaccharineToLambda(n.Returns)
 
 	for i := len(n.Statements) - 1; i >= 0; i-- {
 		result = reduceStatement(n.Statements[i], result)
@@ -94,45 +92,17 @@ func encodeClause(n *saccharine.Clause) lambda.Expression {
 	return result
 }
 
-func encodeExpression(s saccharine.Expression) lambda.Expression {
+func SaccharineToLambda(n saccharine.Expression) lambda.Expression {
-	switch s := s.(type) {
+	switch n := n.(type) {
-	case *saccharine.Atom:
+	case *saccharine.Variable:
-		return encodeAtom(s)
+		return convertAtom(n)
 	case *saccharine.Abstraction:
-		return encodeAbstraction(s)
+		return convertAbstraction(n)
 	case *saccharine.Application:
-		return encodeApplication(s)
+		return convertApplication(n)
 	case *saccharine.Clause:
-		return encodeClause(s)
+		return convertClause(n)
 	default:
-		panic(fmt.Errorf("unknown expression type: %T", s))
+		panic(fmt.Errorf("unknown expression type: %T", n))
 	}
 }
-
-func decodeExression(l lambda.Expression) saccharine.Expression {
-	switch l := l.(type) {
-	case lambda.Variable:
-		return &saccharine.Atom{Name: l.Name}
-	case lambda.Abstraction:
-		return &saccharine.Abstraction{
-			Parameters: []string{l.Parameter},
-			Body:       decodeExression(l.Body)}
-	case lambda.Application:
-		return &saccharine.Application{
-			Abstraction: decodeExression(l.Abstraction),
-			Arguments:   []saccharine.Expression{decodeExression(l.Argument)}}
-	default:
-		panic(fmt.Errorf("unknown expression type: %T", l))
-	}
-}
-
-// Lambda2Saccharine converts a pure lambda calculus expression into its
-// Saccharine counterpart.
-func Lambda2Saccharine(l lambda.Expression) (saccharine.Expression, error) {
-	return decodeExression(l), nil
-}
-
-// Saccharine2Lambda desugars a saccharine expression into pure lambda calculus.
-func Saccharine2Lambda(s saccharine.Expression) (lambda.Expression, error) {
-	return encodeExpression(s), nil
-}

pkg/engine/engine.go

@@ -1,18 +1,23 @@
-// Package engine defines a general process of reducing a lambda calculus
-// expression.
 package engine
 
-// A Process handles the reduction of a single expression.
+import (
-type Process[T any] interface {
+	"fmt"
-	// Get the current state of the process.
-	// Returns an error if the current state cannot be represented.
-	Get() (T, error)
 
-	// Step performs reduction(s) on the representation. If the number of steps
+	"git.maximhutz.com/max/lambda/pkg/repr"
-	// defined is less than zero, it will perform as many reductions as
+)
-	// possible. Returns whether a reduction was performed.
+
-	Step(int) bool
+type Engine[R repr.Repr] interface {
+	Run(trace bool, count int) (Trace, bool)
+	Step() uint64
+	State() (repr.Repr, error)
+
+	fmt.Stringer
 }
 
-// An Engine is an function that generates reduction processes.
+type Trace interface {
-type Engine[T any] = func(T) (Process[T], error)
+	Before() string
+	After() string
+	Step() uint64
+	TransitionName() string
+	TransitionNodes() string
+}

pkg/engine/normalorder/engine.go

@@ -1,42 +0,0 @@
-// Package normalorder contains an engine that reduces a 'lambda.Expression'
-// in the normal order.
-package normalorder
-
-import (
-	"git.maximhutz.com/max/lambda/pkg/engine"
-	"git.maximhutz.com/max/lambda/pkg/lambda"
-)
-
-type process struct {
-	expr lambda.Expression
-}
-
-func (e process) Get() (lambda.Expression, error) {
-	return e.expr, nil
-}
-
-func (e *process) Set(l lambda.Expression) error {
-	e.expr = l
-	return nil
-}
-
-func (e *process) Step(i int) bool {
-	for range i {
-		next, reduced := ReduceOnce(e.expr)
-		if !reduced {
-			return false
-		}
-
-		e.expr = next
-	}
-
-	return true
-}
-
-// NewProcess creates a new redution process.
-func NewProcess(expression lambda.Expression) (engine.Process[lambda.Expression], error) {
-	return &process{expr: expression}, nil
-}
-
-var _ engine.Process[lambda.Expression] = (*process)(nil)
-var _ engine.Engine[lambda.Expression] = NewProcess

pkg/engine/normalorder/reduce_once.go

@@ -1,39 +0,0 @@
-package normalorder
-
-import "git.maximhutz.com/max/lambda/pkg/lambda"
-
-// ReduceOnce attempts to apply a single reduction to a lambda expression.
-// It returns (1) the final expression (reduced, or not), and (2) whether or not
-// a reduction was applied.
-//
-// If a reduction is not applied, it returns the original expression.
-func ReduceOnce(e lambda.Expression) (lambda.Expression, bool) {
-	switch e := e.(type) {
-	case lambda.Abstraction:
-		body, reduced := ReduceOnce(e.Body)
-		if reduced {
-			return lambda.Abstraction{Parameter: e.Parameter, Body: body}, true
-		}
-		return e, false
-
-	case lambda.Application:
-		if fn, fnOk := e.Abstraction.(lambda.Abstraction); fnOk {
-			return lambda.Substitute(fn.Body, fn.Parameter, e.Argument), true
-		}
-
-		abs, reduced := ReduceOnce(e.Abstraction)
-		if reduced {
-			return lambda.Application{Abstraction: abs, Argument: e.Argument}, true
-		}
-
-		arg, reduced := ReduceOnce(e.Argument)
-		if reduced {
-			return lambda.Application{Abstraction: e.Abstraction, Argument: arg}, true
-		}
-
-		return e, false
-
-	default:
-		return e, false
-	}
-}

pkg/iterator/iterator.go

@@ -1,25 +1,35 @@
-// Package iterator defines a generic way to iterator over a slice of data.
+/*
+Package "iterator"
+*/
 package iterator
 
 import "fmt"
 
-// An Iterator traverses over slices.
+// An iterator over slices.
 type Iterator[T any] struct {
 	items []T
 	index int
 }
 
-// Of creates a new iterator, over a set of defined items.
+// Create a new iterator, over a set of items.
 func Of[T any](items []T) *Iterator[T] {
 	return &Iterator[T]{items: items, index: 0}
 }
 
-// Index returns the current position of the iterator.
+// Returns the current position of the iterator.
 func (i Iterator[T]) Index() int {
 	return i.index
 }
 
-// Get returns the datum at the current position of the iterator.
+func (i Iterator[T]) Copy() *Iterator[T] {
+	return &Iterator[T]{items: i.items, index: i.index}
+}
+
+func (i *Iterator[T]) Sync(o *Iterator[T]) {
+	i.index = o.index
+}
+
+// Create a new iterator, over a set of items.
 func (i Iterator[T]) Get() (T, error) {
 	var null T
 	if i.Done() {
@@ -29,26 +39,22 @@ func (i Iterator[T]) Get() (T, error) {
 	return i.items[i.index], nil
 }
 
-// MustGet is a version of Get, that panics if the datum cannot be returned.
 func (i Iterator[T]) MustGet() T {
-	t, err := i.Get()
+	var null T
-	if err != nil {
+	if i.Done() {
-		panic(fmt.Errorf("cannot get current token: %w", err))
+		return null
 	}
 
-	return t
+	return i.items[i.index]
 }
 
-// Forward increments the iterator if the iterator is not yet at the end of the
-// slice.
 func (i *Iterator[T]) Forward() {
 	if !i.Done() {
 		i.index++
 	}
 }
 
-// Next attempts to increment the iterator. Returns an error if it cannot be
+// Create a new iterator, over a set of items.
-// incremented.
 func (i *Iterator[T]) Next() (T, error) {
 	item, err := i.Get()
 	if err == nil {
@@ -58,37 +64,22 @@ func (i *Iterator[T]) Next() (T, error) {
 	return item, err
 }
 
-// Back decrements the iterator. If the iterator is already at the beginning of
+// Create a new iterator, over a set of items.
-// the slice, this is a no-op.
 func (i *Iterator[T]) Back() {
 	i.index = max(i.index-1, 0)
 }
 
-// Done returns whether the iterator is at the end of the slice or not.
+// Returns the current position of the iterator.
 func (i Iterator[T]) Done() bool {
 	return i.index == len(i.items)
 }
 
-// While increments the iterator as long as the current item satisfies the
+func Do[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
-// predicate. The first item that does not match is left unconsumed.
+	i2 := i.Copy()
-func (i *Iterator[T]) While(fn func(T) bool) {
-	for !i.Done() {
-		if !fn(i.MustGet()) {
-			return
-		}
-		i.Forward()
-	}
-}
 
-// Try attempts to perform an operation using the iterator. If the operation
+	out, err := fn(i2)
-// succeeds, the iterator keeps its new position. If the operation fails, the
+	if err == nil {
-// iterator is rolled back, and an error is returned.
+		i.Sync(i2)
-func Try[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
-	saved := i.index
-
-	out, err := fn(i)
-	if err != nil {
-		i.index = saved
 	}
 
 	return out, err

pkg/lambda/codec.go

@@ -1,27 +0,0 @@
-package lambda
-
-import (
-	"git.maximhutz.com/max/lambda/pkg/codec"
-)
-
-// A Codec is a [codec.Codec] that serializes lambda calculus expressions.
-type Codec struct{}
-
-// Decode parses a string as lambda calculus.
-// Returns an error if it cannot.
-func (m Codec) Decode(s string) (Expression, error) {
-	tokens, err := scan(s)
-	if err != nil {
-		return nil, err
-	}
-
-	return parse(tokens)
-}
-
-// Encode turns a lambda calculus expression into a string.
-// Returns an error if it cannot.
-func (m Codec) Encode(e Expression) (string, error) {
-	return Stringify(e), nil
-}
-
-var _ codec.Codec[Expression] = (*Codec)(nil)

pkg/lambda/get_free_variables.go

@@ -1,27 +0,0 @@
-package lambda
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/set"
-)
-
-// GetFree returns the set of all free variable names in the expression.
-// This function does not mutate the input expression.
-// The returned set is newly allocated and can be modified by the caller.
-func GetFree(e Expression) set.Set[string] {
-	switch e := e.(type) {
-	case Variable:
-		return set.New(e.Name)
-	case Abstraction:
-		vars := GetFree(e.Body)
-		vars.Remove(e.Parameter)
-		return vars
-	case Application:
-		vars := GetFree(e.Abstraction)
-		vars.Merge(GetFree(e.Argument))
-		return vars
-	default:
-		panic(fmt.Errorf("unknown expression type: %v", e))
-	}
-}

pkg/lambda/is_free_variable.go

@@ -1,18 +0,0 @@
-package lambda
-
-import "fmt"
-
-// IsFree returns true if the variable name n occurs free in the expression.
-// This function does not mutate the input expression.
-func IsFree(e Expression, n string) bool {
-	switch e := e.(type) {
-	case Variable:
-		return e.Name == n
-	case Abstraction:
-		return e.Parameter != n && IsFree(e.Body, n)
-	case Application:
-		return IsFree(e.Abstraction, n) || IsFree(e.Argument, n)
-	default:
-		panic(fmt.Errorf("unknown expression type: %v", e))
-	}
-}

pkg/lambda/lambda.go

@@ -1,31 +0,0 @@
-// Package lambda defines the AST for the untyped lambda calculus.
-package lambda
-
-// An Expression is a node in the lambda calculus abstract syntax tree.
-// It is a sealed interface; only types in this package may implement it.
-type Expression interface {
-	expression()
-}
-
-// An Abstraction binds a single parameter over a body expression.
-type Abstraction struct {
-	Parameter string
-	Body      Expression
-}
-
-func (a Abstraction) expression() {}
-
-// An Application applies an abstraction to a single argument.
-type Application struct {
-	Abstraction Expression
-	Argument    Expression
-}
-
-func (a Application) expression() {}
-
-// A Variable is a named reference to a bound or free variable.
-type Variable struct {
-	Name string
-}
-
-func (v Variable) expression() {}

pkg/lambda/parse.go

@@ -1,80 +0,0 @@
-package lambda
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-type tokenIterator = iterator.Iterator[lambdaToken]
-
-func parseVariable(i *tokenIterator) (Expression, error) {
-	if tok, err := token.ParseRawToken(i, tokenAtom); err != nil {
-		return nil, fmt.Errorf("expected variable (col %d): %w", i.Index(), err)
-	} else {
-		return Variable{Name: tok.Value}, nil
-	}
-}
-
-func parseAbstraction(i *tokenIterator) (Expression, error) {
-	if _, err := token.ParseRawToken(i, tokenSlash); err != nil {
-		return nil, fmt.Errorf("no backslash (col %d): %w", i.Index(), err)
-	} else if param, err := token.ParseRawToken(i, tokenAtom); err != nil {
-		return nil, fmt.Errorf("no param (col %d): %w", i.Index(), err)
-	} else if _, err := token.ParseRawToken(i, tokenDot); err != nil {
-		return nil, fmt.Errorf("no dot (col %d): %w", i.Index(), err)
-	} else if body, err := parseExpression(i); err != nil {
-		return nil, err
-	} else {
-		return Abstraction{Parameter: param.Value, Body: body}, nil
-	}
-}
-
-func parseApplication(i *tokenIterator) (Expression, error) {
-	if _, err := token.ParseRawToken(i, tokenOpenParen); err != nil {
-		return nil, fmt.Errorf("no opening paren (col %d): %w", i.Index(), err)
-	} else if abstraction, err := parseExpression(i); err != nil {
-		return nil, fmt.Errorf("expected function expression: %w", err)
-	} else if argument, err := parseExpression(i); err != nil {
-		return nil, fmt.Errorf("expected argument expression: %w", err)
-	} else if _, err := token.ParseRawToken(i, tokenCloseParen); err != nil {
-		return nil, fmt.Errorf("no closing paren (col %d): %w", i.Index(), err)
-	} else {
-		return Application{Abstraction: abstraction, Argument: argument}, nil
-	}
-}
-
-func parseExpression(i *tokenIterator) (Expression, error) {
-	peek, err := i.Get()
-	if err != nil {
-		return nil, err
-	}
-
-	switch peek.Type {
-	case tokenOpenParen:
-		return parseApplication(i)
-	case tokenSlash:
-		return parseAbstraction(i)
-	case tokenAtom:
-		return parseVariable(i)
-	default:
-		return nil, fmt.Errorf("expected expression, got '%v' (col %d)", peek.Value, peek.Column)
-	}
-}
-
-// parse converts a token slice into a lambda calculus expression.
-func parse(tokens []lambdaToken) (Expression, error) {
-	i := iterator.Of(tokens)
-
-	exp, err := parseExpression(i)
-	if err != nil {
-		return nil, err
-	}
-
-	if !i.Done() {
-		return nil, fmt.Errorf("expected EOF, found more tokens (col %d)", i.MustGet().Column)
-	}
-
-	return exp, nil
-}

pkg/lambda/rename.go

@@ -1,31 +0,0 @@
-package lambda
-
-import "fmt"
-
-// Rename replaces all occurrences of the target variable name with the new name.
-func Rename(e Expression, target string, newName string) Expression {
-	switch e := e.(type) {
-	case Variable:
-		if e.Name == target {
-			return Variable{Name: newName}
-		}
-
-		return e
-	case Abstraction:
-		newParam := e.Parameter
-		if e.Parameter == target {
-			newParam = newName
-		}
-
-		newBody := Rename(e.Body, target, newName)
-
-		return Abstraction{Parameter: newParam, Body: newBody}
-	case Application:
-		newAbs := Rename(e.Abstraction, target, newName)
-		newArg := Rename(e.Argument, target, newName)
-
-		return Application{Abstraction: newAbs, Argument: newArg}
-	default:
-		panic(fmt.Errorf("unknown expression type: %v", e))
-	}
-}

pkg/lambda/scan.go

@@ -1,45 +0,0 @@
-package lambda
-
-import (
-	"fmt"
-	"unicode"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-// scanToken pulls the next lambda calculus token from a rune iterator.
-func scanToken(i *iterator.Iterator[rune]) (*lambdaToken, error) {
-	index := i.Index()
-
-	if i.Done() {
-		return nil, nil
-	}
-
-	letter, err := i.Next()
-	if err != nil {
-		return nil, fmt.Errorf("cannot produce next token: %w", err)
-	}
-
-	switch {
-	case letter == '(':
-		return token.New(tokenOpenParen, index), nil
-	case letter == ')':
-		return token.New(tokenCloseParen, index), nil
-	case letter == '\\':
-		return token.New(tokenSlash, index), nil
-	case letter == '.':
-		return token.New(tokenDot, index), nil
-	case unicode.IsSpace(letter):
-		return nil, nil
-	case token.IsVariable(letter):
-		return token.ScanAtom(i, letter, tokenAtom, index), nil
-	}
-
-	return nil, fmt.Errorf("unknown character '%v'", string(letter))
-}
-
-// scan tokenizes an input string into lambda calculus tokens.
-func scan(input string) ([]lambdaToken, error) {
-	return token.Scan(input, scanToken)
-}

pkg/lambda/stringify.go

@@ -1,17 +0,0 @@
-package lambda
-
-import "fmt"
-
-// Stringify turns an expression as a string.
-func Stringify(e Expression) string {
-	switch e := e.(type) {
-	case Variable:
-		return e.Name
-	case Abstraction:
-		return "\\" + e.Parameter + "." + Stringify(e.Body)
-	case Application:
-		return "(" + Stringify(e.Abstraction) + " " + Stringify(e.Argument) + ")"
-	default:
-		panic(fmt.Errorf("unknown expression type: %v", e))
-	}
-}

pkg/lambda/substitute.go

@@ -1,41 +0,0 @@
-package lambda
-
-import "fmt"
-
-// Substitute replaces all free occurrences of the target variable with the
-// replacement expression. Alpha-renaming is performed automatically to
-// avoid variable capture.
-func Substitute(e Expression, target string, replacement Expression) Expression {
-	switch e := e.(type) {
-	case Variable:
-		if e.Name == target {
-			return replacement
-		}
-
-		return e
-	case Abstraction:
-		if e.Parameter == target {
-			return e
-		}
-
-		body := e.Body
-		param := e.Parameter
-		if IsFree(replacement, param) {
-			freeVars := GetFree(replacement)
-			freeVars.Merge(GetFree(body))
-			freshVar := GenerateFreshName(freeVars)
-			body = Rename(body, param, freshVar)
-			param = freshVar
-		}
-
-		newBody := Substitute(body, target, replacement)
-		return Abstraction{Parameter: param, Body: newBody}
-	case Application:
-		abs := Substitute(e.Abstraction, target, replacement)
-		arg := Substitute(e.Argument, target, replacement)
-
-		return Application{Abstraction: abs, Argument: arg}
-	default:
-		panic(fmt.Errorf("unknown expression type: %v", e))
-	}
-}

pkg/lambda/token.go

@@ -1,45 +0,0 @@
-package lambda
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-// A tokenType is an identifier for any token in the lambda calculus.
-type tokenType int
-
-// All official tokens of the lambda calculus.
-const (
-	// tokenOpenParen denotes the '(' token.
-	tokenOpenParen tokenType = iota
-	// tokenCloseParen denotes the ')' token.
-	tokenCloseParen
-	// tokenSlash denotes the '\' token.
-	tokenSlash
-	// tokenDot denotes the '.' token.
-	tokenDot
-	// tokenAtom denotes an alpha-numeric variable.
-	tokenAtom
-)
-
-// Name returns the type of the tokenType, as a string.
-func (t tokenType) Name() string {
-	switch t {
-	case tokenOpenParen:
-		return "("
-	case tokenCloseParen:
-		return ")"
-	case tokenSlash:
-		return "\\"
-	case tokenDot:
-		return "."
-	case tokenAtom:
-		return "ATOM"
-	default:
-		panic(fmt.Errorf("unknown token type %v", t))
-	}
-}
-
-// lambdaToken is the concrete token type for the lambda calculus.
-type lambdaToken = token.Token[tokenType]

pkg/repr/lambda/expression.go

@@ -0,0 +1,87 @@
+package lambda
+
+import (
+	"git.maximhutz.com/max/lambda/pkg/repr"
+	"git.maximhutz.com/max/lambda/pkg/set"
+)
+
+// Expression is the interface for all lambda calculus expression types.
+// It embeds the general expr.Expression interface for cross-mode compatibility.
+type Expression interface {
+	repr.Repr
+
+	// Substitute replaces all free occurrences of the target variable with the
+	// replacement expression. Alpha-renaming is performed automatically to
+	// avoid variable capture.
+	Substitute(target string, replacement Expression) Expression
+
+	// GetFree returns the set of all free variable names in the expression.
+	// This function does not mutate the input expression.
+	// The returned set is newly allocated and can be modified by the caller.
+	GetFree() set.Set[string]
+
+	// Rename replaces all occurrences of the target variable name with the new name.
+	Rename(target string, newName string) Expression
+
+	// IsFree returns true if the variable name n occurs free in the expression.
+	// This function does not mutate the input expression.
+	IsFree(n string) bool
+}
+
+var (
+	_ Expression = Abstraction{}
+	_ Expression = Application{}
+	_ Expression = Variable{}
+)
+
+/** ------------------------------------------------------------------------- */
+
+type Abstraction struct {
+	parameter string
+	body      Expression
+}
+
+func (a Abstraction) Parameter() string {
+	return a.parameter
+}
+
+func (a Abstraction) Body() Expression {
+	return a.body
+}
+
+func NewAbstraction(parameter string, body Expression) Abstraction {
+	return Abstraction{parameter, body}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Application struct {
+	abstraction Expression
+	argument    Expression
+}
+
+func (a Application) Abstraction() Expression {
+	return a.abstraction
+}
+
+func (a Application) Argument() Expression {
+	return a.argument
+}
+
+func NewApplication(abstraction Expression, argument Expression) Application {
+	return Application{abstraction, argument}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Variable struct {
+	name string
+}
+
+func (v Variable) Name() string {
+	return v.name
+}
+
+func NewVariable(name string) Variable {
+	return Variable{name}
+}

pkg/repr/lambda/get_free_variables.go

@@ -0,0 +1,19 @@
+package lambda
+
+import "git.maximhutz.com/max/lambda/pkg/set"
+
+func (e Variable) GetFree() set.Set[string] {
+	return set.New(e.Name())
+}
+
+func (e Abstraction) GetFree() set.Set[string] {
+	vars := e.Body().GetFree()
+	vars.Remove(e.Parameter())
+	return vars
+}
+
+func (e Application) GetFree() set.Set[string] {
+	vars := e.Abstraction().GetFree()
+	vars.Merge(e.Argument().GetFree())
+	return vars
+}

pkg/repr/lambda/is_free_variable.go

@@ -0,0 +1,12 @@
+package lambda
+
+func (e Variable) IsFree(n string) bool {
+	return e.Name() == n
+}
+
+func (e Abstraction) IsFree(n string) bool {
+	return e.Parameter() != n && e.Body().IsFree(n)
+}
+func (e Application) IsFree(n string) bool {
+	return e.Abstraction().IsFree(n) || e.Argument().IsFree(n)
+}

pkg/repr/lambda/rename.go

@@ -0,0 +1,28 @@
+package lambda
+
+// Rename replaces all occurrences of the target variable name with the new name.
+func (e Variable) Rename(target string, newName string) Expression {
+	if e.Name() == target {
+		return NewVariable(newName)
+	}
+
+	return e
+}
+
+func (e Abstraction) Rename(target string, newName string) Expression {
+	newParam := e.Parameter()
+	if e.Parameter() == target {
+		newParam = newName
+	}
+
+	newBody := e.Body().Rename(target, newName)
+
+	return NewAbstraction(newParam, newBody)
+}
+
+func (e Application) Rename(target string, newName string) Expression {
+	newAbs := e.Abstraction().Rename(target, newName)
+	newArg := e.Argument().Rename(target, newName)
+
+	return NewApplication(newAbs, newArg)
+}

pkg/repr/lambda/substitute.go

@@ -0,0 +1,35 @@
+package lambda
+
+func (e Variable) Substitute(target string, replacement Expression) Expression {
+	if e.Name() == target {
+		return replacement
+	}
+
+	return e
+}
+
+func (e Abstraction) Substitute(target string, replacement Expression) Expression {
+	if e.Parameter() == target {
+		return e
+	}
+
+	body := e.Body()
+	param := e.Parameter()
+	if replacement.IsFree(param) {
+		freeVars := replacement.GetFree()
+		freeVars.Merge(body.GetFree())
+		freshVar := GenerateFreshName(freeVars)
+		body = body.Rename(param, freshVar)
+		param = freshVar
+	}
+
+	newBody := body.Substitute(target, replacement)
+	return NewAbstraction(param, newBody)
+}
+
+func (e Application) Substitute(target string, replacement Expression) Expression {
+	abs := e.Abstraction().Substitute(target, replacement)
+	arg := e.Argument().Substitute(target, replacement)
+
+	return NewApplication(abs, arg)
+}

pkg/repr/repr.go

@@ -0,0 +1,4 @@
+package repr
+
+type Repr interface {
+}

pkg/repr/saccharine/expression.go

@@ -0,0 +1,59 @@
+package saccharine
+
+import (
+	"git.maximhutz.com/max/lambda/pkg/repr"
+)
+
+type Expression interface {
+	repr.Repr
+}
+
+var (
+	_ Expression = Abstraction{}
+	_ Expression = Application{}
+	_ Expression = Variable{}
+	_ Expression = Clause{}
+)
+
+/** ------------------------------------------------------------------------- */
+
+type Abstraction struct {
+	Parameters []string
+	Body       Expression
+}
+
+func NewAbstraction(parameter []string, body Expression) *Abstraction {
+	return &Abstraction{Parameters: parameter, Body: body}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Application struct {
+	Abstraction Expression
+	Arguments   []Expression
+}
+
+func NewApplication(abstraction Expression, arguments []Expression) *Application {
+	return &Application{Abstraction: abstraction, Arguments: arguments}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Variable struct {
+	Name string
+}
+
+func NewVariable(name string) *Variable {
+	return &Variable{Name: name}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type Clause struct {
+	Statements []Statement
+	Returns    Expression
+}
+
+func NewClause(statements []Statement, returns Expression) *Clause {
+	return &Clause{Statements: statements, Returns: returns}
+}

pkg/repr/saccharine/parse.go

@@ -0,0 +1,237 @@
+package saccharine
+
+import (
+	"errors"
+	"fmt"
+
+	"git.maximhutz.com/max/lambda/pkg/iterator"
+	"git.maximhutz.com/max/lambda/pkg/trace"
+)
+
+type TokenIterator = iterator.Iterator[Token]
+
+func parseRawToken(i *TokenIterator, expected Type) (*Token, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*Token, error) {
+		if tok, err := i.Next(); err != nil {
+			return nil, err
+		} else if tok.Type != expected {
+			return nil, fmt.Errorf("expected token %v, got %v'", Name(expected), tok.Value)
+		} else {
+			return &tok, nil
+		}
+	})
+}
+
+func passSoftBreaks(i *TokenIterator) {
+	for {
+		if _, err := parseRawToken(i, TokenSoftBreak); err != nil {
+			return
+		}
+	}
+}
+
+func parseToken(i *TokenIterator, expected Type, ignoreSoftBreaks bool) (*Token, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*Token, error) {
+		if ignoreSoftBreaks {
+			passSoftBreaks(i)
+		}
+
+		return parseRawToken(i, expected)
+	})
+}
+
+func parseString(i *TokenIterator) (string, error) {
+	if tok, err := parseToken(i, TokenAtom, true); err != nil {
+		return "", trace.Wrap(err, "no variable (col %d)", i.Index())
+	} else {
+		return tok.Value, nil
+	}
+}
+
+func parseBreak(i *TokenIterator) (*Token, error) {
+	if tok, softErr := parseRawToken(i, TokenSoftBreak); softErr == nil {
+		return tok, nil
+	} else if tok, hardErr := parseRawToken(i, TokenHardBreak); hardErr == nil {
+		return tok, nil
+	} else {
+		return nil, errors.Join(softErr, hardErr)
+	}
+}
+
+func parseList[U any](i *TokenIterator, fn func(*TokenIterator) (U, error), minimum int) ([]U, error) {
+	results := []U{}
+
+	for {
+		if u, err := fn(i); err != nil {
+			if len(results) < minimum {
+				return nil, trace.Wrap(err, "expected at least '%v' items, got only '%v'", minimum, len(results))
+			}
+			return results, nil
+		} else {
+			results = append(results, u)
+		}
+	}
+}
+
+func parseAbstraction(i *TokenIterator) (*Abstraction, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*Abstraction, error) {
+		if _, err := parseToken(i, TokenSlash, true); err != nil {
+			return nil, trace.Wrap(err, "no function slash (col %d)", i.MustGet().Column)
+		} else if parameters, err := parseList(i, parseString, 0); err != nil {
+			return nil, err
+		} else if _, err = parseToken(i, TokenDot, true); err != nil {
+			return nil, trace.Wrap(err, "no function dot (col %d)", i.MustGet().Column)
+		} else if body, err := parseExpression(i); err != nil {
+			return nil, err
+		} else {
+			return NewAbstraction(parameters, body), nil
+		}
+	})
+}
+
+func parseApplication(i *TokenIterator) (*Application, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*Application, error) {
+		if _, err := parseToken(i, TokenOpenParen, true); err != nil {
+			return nil, trace.Wrap(err, "no openning brackets (col %d)", i.MustGet().Column)
+		} else if expressions, err := parseList(i, parseExpression, 1); err != nil {
+			return nil, err
+		} else if _, err := parseToken(i, TokenCloseParen, true); err != nil {
+			return nil, trace.Wrap(err, "no closing brackets (col %d)", i.MustGet().Column)
+		} else {
+			return NewApplication(expressions[0], expressions[1:]), nil
+		}
+	})
+}
+
+func parseAtom(i *TokenIterator) (*Variable, error) {
+	if tok, err := parseToken(i, TokenAtom, true); err != nil {
+		return nil, trace.Wrap(err, "no variable (col %d)", i.Index())
+	} else {
+		return NewVariable(tok.Value), nil
+	}
+}
+
+func parseStatements(i *TokenIterator) ([]Statement, error) {
+	statements := []Statement{}
+
+	//nolint:errcheck
+	parseList(i, parseBreak, 0)
+
+	for {
+		if statement, err := parseStatement(i); err != nil {
+			break
+		} else if _, err := parseList(i, parseBreak, 1); err != nil && !i.Done() {
+			break
+		} else {
+			statements = append(statements, statement)
+		}
+	}
+
+	return statements, nil
+}
+
+func parseClause(i *TokenIterator, braces bool) (*Clause, error) {
+	if braces {
+		if _, err := parseToken(i, TokenOpenBrace, true); err != nil {
+			return nil, err
+		}
+	}
+
+	var stmts []Statement
+	var last *DeclareStatement
+	var err error
+	var ok bool
+
+	if stmts, err = parseStatements(i); err != nil {
+		return nil, err
+	} else if len(stmts) == 0 {
+		return nil, fmt.Errorf("no statements in clause")
+	} else if last, ok = stmts[len(stmts)-1].(*DeclareStatement); !ok {
+		return nil, fmt.Errorf("this clause contains no final return value (col %d)", i.MustGet().Column)
+	}
+
+	if braces {
+		if _, err := parseToken(i, TokenCloseBrace, true); err != nil {
+			return nil, err
+		}
+	}
+
+	return NewClause(stmts[:len(stmts)-1], last.Value), nil
+}
+
+func parseExpression(i *TokenIterator) (Expression, error) {
+	return iterator.Do(i, func(i *TokenIterator) (Expression, error) {
+		passSoftBreaks(i)
+
+		switch peek := i.MustGet(); peek.Type {
+		case TokenOpenParen:
+			return parseApplication(i)
+		case TokenSlash:
+			return parseAbstraction(i)
+		case TokenAtom:
+			return parseAtom(i)
+		case TokenOpenBrace:
+			return parseClause(i, true)
+		default:
+			return nil, fmt.Errorf("expected expression, got '%v' (col %d)", peek.Value, peek.Column)
+		}
+	})
+}
+
+func parseLet(i *TokenIterator) (*LetStatement, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*LetStatement, error) {
+		if parameters, err := parseList(i, parseString, 1); err != nil {
+			return nil, err
+		} else if _, err := parseToken(i, TokenAssign, true); err != nil {
+			return nil, err
+		} else if body, err := parseExpression(i); err != nil {
+			return nil, err
+		} else {
+			return NewLet(parameters[0], parameters[1:], body), nil
+		}
+	})
+}
+
+func parseDeclare(i *TokenIterator) (*DeclareStatement, error) {
+	if value, err := parseExpression(i); err != nil {
+		return nil, err
+	} else {
+		return NewDeclare(value), nil
+	}
+}
+
+func parseStatement(i *TokenIterator) (Statement, error) {
+	if let, letErr := parseLet(i); letErr == nil {
+		return let, nil
+	} else if declare, declErr := parseDeclare(i); declErr == nil {
+		return declare, nil
+	} else {
+		return nil, errors.Join(letErr, declErr)
+	}
+}
+
+// Given a list of tokens, attempt to parse it into an syntax tree.
+func parse(tokens []Token) (Expression, error) {
+	i := iterator.Of(tokens)
+
+	exp, err := parseClause(i, false)
+	if err != nil {
+		return nil, err
+	}
+
+	if !i.Done() {
+		return nil, fmt.Errorf("expected EOF, found more code (col %d)", i.MustGet().Column)
+	}
+
+	return exp, nil
+}
+
+// Convert a piece of valid saccharine code into an expression.
+func Parse(code string) (Expression, error) {
+	tokens, err := Scan(code)
+	if err != nil {
+		return nil, err
+	}
+
+	return parse(tokens)
+}

pkg/repr/saccharine/scan.go

@@ -0,0 +1,130 @@
+package saccharine
+
+import (
+	"errors"
+	"fmt"
+	"unicode"
+
+	"git.maximhutz.com/max/lambda/pkg/iterator"
+	"git.maximhutz.com/max/lambda/pkg/trace"
+)
+
+// isVariables determines whether a rune can be a valid variable.
+func isVariable(r rune) bool {
+	return unicode.IsLetter(r) || unicode.IsNumber(r)
+}
+
+func scanRune(i *iterator.Iterator[rune], expected func(rune) bool) (rune, error) {
+	i2 := i.Copy()
+
+	if r, err := i2.Next(); err != nil {
+		return r, err
+	} else if !expected(r) {
+		return r, fmt.Errorf("got unexpected rune %v'", r)
+	} else {
+		i.Sync(i2)
+		return r, nil
+	}
+}
+
+func scanCharacter(i *iterator.Iterator[rune], expected rune) (rune, error) {
+	i2 := i.Copy()
+
+	if r, err := i2.Next(); err != nil {
+		return r, err
+	} else if r != expected {
+		return r, fmt.Errorf("got unexpected rune %v'", r)
+	} else {
+		i.Sync(i2)
+		return r, nil
+	}
+}
+
+// Pulls the next token from an iterator over runes. If it cannot, it will
+// return nil. If an error occurs, it will return that.
+func scanToken(i *iterator.Iterator[rune]) (*Token, error) {
+	index := i.Index()
+
+	if i.Done() {
+		return nil, nil
+	}
+
+	letter, err := i.Next()
+	if err != nil {
+		return nil, trace.Wrap(err, "cannot produce next token")
+	}
+
+	switch {
+	case letter == '(':
+		return NewOpenParen(index), nil
+	case letter == ')':
+		return NewCloseParen(index), nil
+	case letter == '.':
+		return NewDot(index), nil
+	case letter == '\\':
+		return NewSlash(index), nil
+	case letter == '\n':
+		return NewSoftBreak(index), nil
+	case letter == '{':
+		return NewOpenBrace(index), nil
+	case letter == '}':
+		return NewCloseBrace(index), nil
+	case letter == ':':
+		if _, err := scanCharacter(i, '='); err != nil {
+			return nil, err
+		} else {
+			return NewAssign(index), nil
+		}
+	case letter == ';':
+		return NewHardBreak(index), nil
+	case letter == '#':
+		// Skip everything until the next newline or EOF.
+		for !i.Done() {
+			r, err := i.Next()
+			if err != nil {
+				return nil, trace.Wrap(err, "error while parsing comment")
+			}
+
+			if r == '\n' {
+				// Put the newline back so it can be processed as a soft break.
+				i.Back()
+				break
+			}
+		}
+		return nil, nil
+	case unicode.IsSpace(letter):
+		return nil, nil
+	case isVariable(letter):
+		atom := []rune{letter}
+
+		for {
+			if r, err := scanRune(i, isVariable); err != nil {
+				break
+			} else {
+				atom = append(atom, r)
+			}
+		}
+
+		return NewAtom(string(atom), index), nil
+	}
+
+	return nil, fmt.Errorf("unknown character '%v'", string(letter))
+}
+
+// Parse a string into tokens.
+func Scan(input string) ([]Token, error) {
+	i := iterator.Of([]rune(input))
+	tokens := []Token{}
+	errorList := []error{}
+
+	for !i.Done() {
+		token, err := scanToken(i)
+		if err != nil {
+			errorList = append(errorList, err)
+		} else if token != nil {
+			tokens = append(tokens, *token)
+		}
+	}
+
+	return tokens, errors.Join(errorList...)
+}

pkg/repr/saccharine/statement.go

@@ -0,0 +1,31 @@
+package saccharine
+
+import (
+	"git.maximhutz.com/max/lambda/pkg/repr"
+)
+
+type Statement interface {
+	repr.Repr
+}
+
+/** ------------------------------------------------------------------------- */
+
+type LetStatement struct {
+	Name       string
+	Parameters []string
+	Body       Expression
+}
+
+func NewLet(name string, parameters []string, body Expression) *LetStatement {
+	return &LetStatement{Name: name, Parameters: parameters, Body: body}
+}
+
+/** ------------------------------------------------------------------------- */
+
+type DeclareStatement struct {
+	Value Expression
+}
+
+func NewDeclare(value Expression) *DeclareStatement {
+	return &DeclareStatement{Value: value}
+}

pkg/repr/saccharine/stringify.go

@@ -5,30 +5,30 @@ import (
 	"strings"
 )
 
-func stringifyAtom(n *Atom) string {
+func stringifyAtom(n *Variable) string {
 	return n.Name
 }
 
 func stringifyAbstraction(n *Abstraction) string {
-	return "\\" + strings.Join(n.Parameters, " ") + "." + stringifyExpression(n.Body)
+	return "\\" + strings.Join(n.Parameters, " ") + "." + Stringify(n.Body)
 }
 
 func stringifyApplication(n *Application) string {
-	arguments := []string{stringifyExpression(n.Abstraction)}
+	arguments := []string{Stringify(n.Abstraction)}
 
 	for _, argument := range n.Arguments {
-		arguments = append(arguments, stringifyExpression(argument))
+		arguments = append(arguments, Stringify(argument))
 	}
 
 	return "(" + strings.Join(arguments, " ") + ")"
 }
 
 func stringifyLet(s *LetStatement) string {
-	return s.Name + " " + strings.Join(s.Parameters, " ") + " := " + stringifyExpression(s.Body)
+	return s.Name + " " + strings.Join(s.Parameters, " ") + " := " + Stringify(s.Body)
 }
 
 func stringifyDeclare(s *DeclareStatement) string {
-	return stringifyExpression(s.Value)
+	return Stringify(s.Value)
 }
 
 func stringifyStatement(s Statement) string {
@@ -49,13 +49,13 @@ func stringifyClause(n *Clause) string {
 		stmts += stringifyStatement(statement) + "; "
 	}
 
-	return "{ " + stmts + stringifyExpression(n.Returns) + " }"
+	return "{ " + stmts + Stringify(n.Returns) + " }"
 }
 
 // Convert an expression back into valid source code.
-func stringifyExpression(n Expression) string {
+func Stringify(n Expression) string {
 	switch n := n.(type) {
-	case *Atom:
+	case *Variable:
 		return stringifyAtom(n)
 	case *Abstraction:
 		return stringifyAbstraction(n)

pkg/repr/saccharine/token.go

@@ -0,0 +1,91 @@
+package saccharine
+
+import "fmt"
+
+// All tokens in the pseudo-lambda language.
+type Type int
+
+const (
+	TokenOpenParen  Type = iota // Denotes the '(' token.
+	TokenCloseParen             // Denotes the ')' token.
+	TokenOpenBrace              // Denotes the '{' token.
+	TokenCloseBrace             // Denotes the '}' token.
+	TokenHardBreak              // Denotes the ';' token.
+	TokenAssign                 // Denotes the ':=' token.
+	TokenAtom                   // Denotes an alpha-numeric variable.
+	TokenSlash                  // Denotes the '/' token.
+	TokenDot                    // Denotes the '.' token.
+	TokenSoftBreak              // Denotes a new-line.
+)
+
+// A representation of a token in source code.
+type Token struct {
+	Column int    // Where the token begins in the source text.
+	Type   Type   // What type the token is.
+	Value  string // The value of the token.
+}
+
+func NewOpenParen(column int) *Token {
+	return &Token{Type: TokenOpenParen, Column: column, Value: "("}
+}
+
+func NewCloseParen(column int) *Token {
+	return &Token{Type: TokenCloseParen, Column: column, Value: ")"}
+}
+
+func NewOpenBrace(column int) *Token {
+	return &Token{Type: TokenOpenBrace, Column: column, Value: "{"}
+}
+
+func NewCloseBrace(column int) *Token {
+	return &Token{Type: TokenCloseBrace, Column: column, Value: "}"}
+}
+
+func NewDot(column int) *Token {
+	return &Token{Type: TokenDot, Column: column, Value: "."}
+}
+
+func NewHardBreak(column int) *Token {
+	return &Token{Type: TokenHardBreak, Column: column, Value: ";"}
+}
+
+func NewAssign(column int) *Token {
+	return &Token{Type: TokenAssign, Column: column, Value: ":="}
+}
+
+func NewSlash(column int) *Token {
+	return &Token{Type: TokenSlash, Column: column, Value: "\\"}
+}
+
+func NewAtom(name string, column int) *Token {
+	return &Token{Type: TokenAtom, Column: column, Value: name}
+}
+
+func NewSoftBreak(column int) *Token {
+	return &Token{Type: TokenSoftBreak, Column: column, Value: "\\n"}
+}
+
+func Name(typ Type) string {
+	switch typ {
+	case TokenOpenParen:
+		return "("
+	case TokenCloseParen:
+		return ")"
+	case TokenSlash:
+		return "\\"
+	case TokenDot:
+		return "."
+	case TokenAtom:
+		return "ATOM"
+	case TokenSoftBreak:
+		return "\\n"
+	case TokenHardBreak:
+		return ";"
+	default:
+		panic(fmt.Errorf("unknown token type %v", typ))
+	}
+}
+
+func (t Token) Name() string {
+	return Name(t.Type)
+}

pkg/saccharine/codec.go

@@ -1,27 +0,0 @@
-package saccharine
-
-import (
-	"git.maximhutz.com/max/lambda/pkg/codec"
-)
-
-// A Codec is a [codec.Codec] that serializes Saccharine expressions.
-type Codec struct{}
-
-// Decode parses a string as Saccharine source code. Returns an error
-// if it cannot.
-func (c Codec) Decode(s string) (Expression, error) {
-	tokens, err := scan(s)
-	if err != nil {
-		return nil, err
-	}
-
-	return parse(tokens)
-}
-
-// Encode turns a Saccharine expression into a string. Returns an error if it
-// cannot.
-func (c Codec) Encode(e Expression) (string, error) {
-	return stringifyExpression(e), nil
-}
-
-var _ codec.Codec[Expression] = (*Codec)(nil)

pkg/saccharine/parse.go

@@ -1,194 +0,0 @@
-package saccharine
-
-import (
-	"errors"
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-type tokenIterator = iterator.Iterator[Token]
-
-func passSoftBreaks(i *tokenIterator) {
-	for {
-		if _, err := token.ParseRawToken(i, TokenSoftBreak); err != nil {
-			return
-		}
-	}
-}
-
-func parseToken(i *tokenIterator, expected TokenType, ignoreSoftBreaks bool) (*Token, error) {
-	if ignoreSoftBreaks {
-		passSoftBreaks(i)
-	}
-
-	return token.ParseRawToken(i, expected)
-}
-
-func parseString(i *tokenIterator) (string, error) {
-	if tok, err := parseToken(i, TokenAtom, true); err != nil {
-		return "", fmt.Errorf("no variable (col %d): %w", i.Index(), err)
-	} else {
-		return tok.Value, nil
-	}
-}
-
-func parseBreak(i *tokenIterator) (*Token, error) {
-	if tok, softErr := token.ParseRawToken(i, TokenSoftBreak); softErr == nil {
-		return tok, nil
-	} else if tok, hardErr := token.ParseRawToken(i, TokenHardBreak); hardErr == nil {
-		return tok, nil
-	} else {
-		return nil, errors.Join(softErr, hardErr)
-	}
-}
-
-func parseAbstraction(i *tokenIterator) (*Abstraction, error) {
-	if _, err := parseToken(i, TokenSlash, true); err != nil {
-		return nil, fmt.Errorf("no function slash (col %d): %w", i.MustGet().Column, err)
-	} else if parameters, err := token.ParseList(i, parseString, 0); err != nil {
-		return nil, err
-	} else if _, err = parseToken(i, TokenDot, true); err != nil {
-		return nil, fmt.Errorf("no function dot (col %d): %w", i.MustGet().Column, err)
-	} else if body, err := parseExpression(i); err != nil {
-		return nil, err
-	} else {
-		return &Abstraction{Parameters: parameters, Body: body}, nil
-	}
-}
-
-func parseApplication(i *tokenIterator) (*Application, error) {
-	if _, err := parseToken(i, TokenOpenParen, true); err != nil {
-		return nil, fmt.Errorf("no openning brackets (col %d): %w", i.MustGet().Column, err)
-	} else if expressions, err := token.ParseList(i, parseExpression, 1); err != nil {
-		return nil, err
-	} else if _, err := parseToken(i, TokenCloseParen, true); err != nil {
-		return nil, fmt.Errorf("no closing brackets (col %d): %w", i.MustGet().Column, err)
-	} else {
-		return &Application{Abstraction: expressions[0], Arguments: expressions[1:]}, nil
-	}
-}
-
-func parseAtom(i *tokenIterator) (*Atom, error) {
-	if tok, err := parseToken(i, TokenAtom, true); err != nil {
-		return nil, fmt.Errorf("no variable (col %d): %w", i.Index(), err)
-	} else {
-		return &Atom{Name: tok.Value}, nil
-	}
-}
-
-func parseStatements(i *tokenIterator) ([]Statement, error) {
-	statements := []Statement{}
-
-	//nolint:errcheck
-	token.ParseList(i, parseBreak, 0)
-
-	for {
-		if statement, err := parseStatement(i); err != nil {
-			break
-		} else if _, err := token.ParseList(i, parseBreak, 1); err != nil && !i.Done() {
-			break
-		} else {
-			statements = append(statements, statement)
-		}
-	}
-
-	return statements, nil
-}
-
-func parseClause(i *tokenIterator, braces bool) (*Clause, error) {
-	if braces {
-		if _, err := parseToken(i, TokenOpenBrace, true); err != nil {
-			return nil, err
-		}
-	}
-
-	var stmts []Statement
-	var last *DeclareStatement
-	var err error
-	var ok bool
-
-	if stmts, err = parseStatements(i); err != nil {
-		return nil, err
-	} else if len(stmts) == 0 {
-		return nil, fmt.Errorf("no statements in clause")
-	} else if last, ok = stmts[len(stmts)-1].(*DeclareStatement); !ok {
-		return nil, fmt.Errorf("this clause contains no final return value (col %d)", i.MustGet().Column)
-	}
-
-	if braces {
-		if _, err := parseToken(i, TokenCloseBrace, true); err != nil {
-			return nil, err
-		}
-	}
-
-	return &Clause{Statements: stmts[:len(stmts)-1], Returns: last.Value}, nil
-}
-
-func parseExpression(i *tokenIterator) (Expression, error) {
-	passSoftBreaks(i)
-
-	if i.Done() {
-		return nil, fmt.Errorf("unexpected end of input")
-	}
-
-	switch peek := i.MustGet(); peek.Type {
-	case TokenOpenParen:
-		return parseApplication(i)
-	case TokenSlash:
-		return parseAbstraction(i)
-	case TokenAtom:
-		return parseAtom(i)
-	case TokenOpenBrace:
-		return parseClause(i, true)
-	default:
-		return nil, fmt.Errorf("expected expression, got '%v' (col %d)", peek.Value, peek.Column)
-	}
-}
-
-func parseLet(i *tokenIterator) (*LetStatement, error) {
-	if parameters, err := token.ParseList(i, parseString, 1); err != nil {
-		return nil, err
-	} else if _, err := parseToken(i, TokenAssign, true); err != nil {
-		return nil, err
-	} else if body, err := parseExpression(i); err != nil {
-		return nil, err
-	} else {
-		return &LetStatement{Name: parameters[0], Parameters: parameters[1:], Body: body}, nil
-	}
-}
-
-func parseDeclare(i *tokenIterator) (*DeclareStatement, error) {
-	if value, err := parseExpression(i); err != nil {
-		return nil, err
-	} else {
-		return &DeclareStatement{Value: value}, nil
-	}
-}
-
-func parseStatement(i *tokenIterator) (Statement, error) {
-	if let, letErr := iterator.Try(i, parseLet); letErr == nil {
-		return let, nil
-	} else if declare, declErr := iterator.Try(i, parseDeclare); declErr == nil {
-		return declare, nil
-	} else {
-		return nil, errors.Join(letErr, declErr)
-	}
-}
-
-// Given a list of tokens, attempt to parse it into an syntax tree.
-func parse(tokens []Token) (Expression, error) {
-	i := iterator.Of(tokens)
-
-	exp, err := parseClause(i, false)
-	if err != nil {
-		return nil, err
-	}
-
-	if !i.Done() {
-		return nil, fmt.Errorf("expected EOF, found more code (col %d)", i.MustGet().Column)
-	}
-
-	return exp, nil
-}

pkg/saccharine/saccharine.go

@@ -1,60 +0,0 @@
-// Package saccharine defines the AST for the Saccharine language, a sugared
-// lambda calculus with let bindings and multi-statement clauses.
-package saccharine
-
-// An Expression is a node in the Saccharine abstract syntax tree.
-// It is a sealed interface; only types in this package may implement it.
-type Expression interface {
-	expression()
-}
-
-// An Abstraction is a lambda expression with zero or more parameters.
-// A zero-parameter abstraction is treated as a thunk.
-type Abstraction struct {
-	Parameters []string
-	Body       Expression
-}
-
-// An Application applies an expression to zero or more arguments.
-type Application struct {
-	Abstraction Expression
-	Arguments   []Expression
-}
-
-// An Atom is a named variable.
-type Atom struct {
-	Name string
-}
-
-// A Clause is a sequence of statements followed by a return expression.
-type Clause struct {
-	Statements []Statement
-	Returns    Expression
-}
-
-func (Abstraction) expression() {}
-func (Application) expression() {}
-func (Atom) expression()        {}
-func (Clause) expression()      {}
-
-// A Statement is a declaration within a Clause.
-// It is a sealed interface; only types in this package may implement it.
-type Statement interface {
-	statement()
-}
-
-// A LetStatement binds a name (with optional parameters) to an expression.
-type LetStatement struct {
-	Name       string
-	Parameters []string
-	Body       Expression
-}
-
-// A DeclareStatement evaluates an expression for its side effects within a
-// clause.
-type DeclareStatement struct {
-	Value Expression
-}
-
-func (LetStatement) statement()     {}
-func (DeclareStatement) statement() {}

pkg/saccharine/scan.go

@@ -1,64 +0,0 @@
-package saccharine
-
-import (
-	"fmt"
-	"unicode"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-// Pulls the next token from an iterator over runes. If it cannot, it will
-// return nil. If an error occurs, it will return that.
-func scanToken(i *iterator.Iterator[rune]) (*Token, error) {
-	index := i.Index()
-
-	if i.Done() {
-		return nil, nil
-	}
-
-	letter, err := i.Next()
-	if err != nil {
-		return nil, fmt.Errorf("cannot produce next token: %w", err)
-	}
-
-	switch {
-	case letter == '(':
-		return token.New(TokenOpenParen, index), nil
-	case letter == ')':
-		return token.New(TokenCloseParen, index), nil
-	case letter == '.':
-		return token.New(TokenDot, index), nil
-	case letter == '\\':
-		return token.New(TokenSlash, index), nil
-	case letter == '\n':
-		return token.New(TokenSoftBreak, index), nil
-	case letter == '{':
-		return token.New(TokenOpenBrace, index), nil
-	case letter == '}':
-		return token.New(TokenCloseBrace, index), nil
-	case letter == ':':
-		if _, err := token.ScanCharacter(i, '='); err != nil {
-			return nil, err
-		} else {
-			return token.New(TokenAssign, index), nil
-		}
-	case letter == ';':
-		return token.New(TokenHardBreak, index), nil
-	case letter == '#':
-		// Skip everything until the next newline or EOF.
-		i.While(func(r rune) bool { return r != '\n' })
-		return nil, nil
-	case unicode.IsSpace(letter):
-		return nil, nil
-	case token.IsVariable(letter):
-		return token.ScanAtom(i, letter, TokenAtom, index), nil
-	}
-
-	return nil, fmt.Errorf("unknown character '%v'", string(letter))
-}
-
-// scan a string into tokens.
-func scan(input string) ([]Token, error) {
-	return token.Scan(input, scanToken)
-}

pkg/saccharine/token.go

@@ -1,65 +0,0 @@
-package saccharine
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/token"
-)
-
-// A TokenType is an identifier for any token in the Saccharine language.
-type TokenType int
-
-// All official tokens of the Saccharine language.
-const (
-	// TokenOpenParen denotes the '(' token.
-	TokenOpenParen TokenType = iota
-	// TokenCloseParen denotes the ')' token.
-	TokenCloseParen
-	// TokenOpenBrace denotes the '{' token.
-	TokenOpenBrace
-	// TokenCloseBrace denotes the '}' token.
-	TokenCloseBrace
-	// TokenHardBreak denotes the ';' token.
-	TokenHardBreak
-	// TokenAssign denotes the ':=' token.
-	TokenAssign
-	// TokenAtom denotes an alpha-numeric variable.
-	TokenAtom
-	// TokenSlash denotes the '\\' token.
-	TokenSlash
-	// TokenDot denotes the '.' token.
-	TokenDot
-	// TokenSoftBreak denotes a new-line.
-	TokenSoftBreak
-)
-
-// Name returns the type of the TokenType, as a string.
-func (t TokenType) Name() string {
-	switch t {
-	case TokenOpenParen:
-		return "("
-	case TokenCloseParen:
-		return ")"
-	case TokenOpenBrace:
-		return "{"
-	case TokenCloseBrace:
-		return "}"
-	case TokenHardBreak:
-		return ";"
-	case TokenAssign:
-		return ":="
-	case TokenAtom:
-		return "ATOM"
-	case TokenSlash:
-		return "\\"
-	case TokenDot:
-		return "."
-	case TokenSoftBreak:
-		return "\\n"
-	default:
-		panic(fmt.Errorf("unknown token type %v", t))
-	}
-}
-
-// Token is the concrete token type for the Saccharine language.
-type Token = token.Token[TokenType]

pkg/set/set.go

@@ -1,41 +1,31 @@
-// Package set defines a generic, mutable unordered set data structure.
 package set
 
 import "iter"
 
-// A Set is an implementation of an mutable, unordered set. It uses a Golang map
-// as its underlying data structure.
 type Set[T comparable] map[T]bool
 
-// Add appends a list of items into the set.
 func (s Set[T]) Add(items ...T) {
 	for _, item := range items {
 		s[item] = true
 	}
 }
 
-// Has returns true an item is present in the set.
 func (s Set[T]) Has(item T) bool {
 	return s[item]
 }
 
-// Remove deletes a list of items from the set.
 func (s Set[T]) Remove(items ...T) {
 	for _, item := range items {
 		delete(s, item)
 	}
 }
 
-// Merge adds all items in the argument into the set. The argument is not
-// mutated.
 func (s Set[T]) Merge(o Set[T]) {
 	for item := range o {
 		s.Add(item)
 	}
 }
 
-// ToList returns all items present in the set, as a slice. The order of the
-// items is not guaranteed.
 func (s Set[T]) ToList() []T {
 	list := []T{}
 
@@ -46,8 +36,6 @@ func (s Set[T]) ToList() []T {
 	return list
 }
 
-// Items returns a sequence of all items present in the set. The order of the
-// items is not guaranteed.
 func (s Set[T]) Items() iter.Seq[T] {
 	return func(yield func(T) bool) {
 		for item := range s {
@@ -58,7 +46,6 @@ func (s Set[T]) Items() iter.Seq[T] {
 	}
 }
 
-// New creates a set of all items as argument.
 func New[T comparable](items ...T) Set[T] {
 	result := Set[T]{}
 

pkg/token/parse.go

@@ -1,42 +0,0 @@
-package token
-
-import (
-	"fmt"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-)
-
-// ParseRawToken consumes the next token from the iterator if its type matches
-// the expected type.
-// Returns an error if the iterator is exhausted or the token type does not
-// match.
-func ParseRawToken[T Type](i *iterator.Iterator[Token[T]], expected T) (*Token[T], error) {
-	tok, err := i.Get()
-	if err != nil {
-		return nil, err
-	}
-	if tok.Type != expected {
-		return nil, fmt.Errorf("expected token %v, got %v'", expected.Name(), tok.Value)
-	}
-	i.Forward()
-	return &tok, nil
-}
-
-// ParseList repeatedly applies a parse function, collecting results into a
-// slice.
-// Stops when the parse function returns an error.
-// Returns an error if fewer than minimum results are collected.
-func ParseList[T Type, U any](i *iterator.Iterator[Token[T]], fn func(*iterator.Iterator[Token[T]]) (U, error), minimum int) ([]U, error) {
-	results := []U{}
-
-	for {
-		if u, err := fn(i); err != nil {
-			if len(results) < minimum {
-				return nil, fmt.Errorf("expected at least '%v' items, got only '%v': %w", minimum, len(results), err)
-			}
-			return results, nil
-		} else {
-			results = append(results, u)
-		}
-	}
-}

pkg/token/scan.go

@@ -1,74 +0,0 @@
-package token
-
-import (
-	"errors"
-	"fmt"
-	"unicode"
-
-	"git.maximhutz.com/max/lambda/pkg/iterator"
-)
-
-// IsVariable determines whether a rune can be a valid variable character.
-func IsVariable(r rune) bool {
-	return unicode.IsLetter(r) || unicode.IsNumber(r) || r == '_'
-}
-
-// ScanRune consumes the next rune from the iterator if it satisfies the
-// predicate.
-// Returns an error if the iterator is exhausted or the rune does not match.
-func ScanRune(i *iterator.Iterator[rune], expected func(rune) bool) (rune, error) {
-	r, err := i.Get()
-	if err != nil {
-		return r, err
-	}
-	if !expected(r) {
-		return r, fmt.Errorf("got unexpected rune %v'", r)
-	}
-	i.Forward()
-	return r, nil
-}
-
-// ScanCharacter consumes the next rune from the iterator if it matches the
-// expected rune exactly.
-// Returns an error if the iterator is exhausted or the rune does not match.
-func ScanCharacter(i *iterator.Iterator[rune], expected rune) (rune, error) {
-	return ScanRune(i, func(r rune) bool { return r == expected })
-}
-
-// ScanAtom scans a contiguous sequence of variable characters into a single
-// atom token.
-// The first rune has already been consumed and is passed in.
-func ScanAtom[T Type](i *iterator.Iterator[rune], first rune, typ T, column int) *Token[T] {
-	atom := []rune{first}
-
-	for {
-		if r, err := ScanRune(i, IsVariable); err != nil {
-			break
-		} else {
-			atom = append(atom, r)
-		}
-	}
-
-	return NewAtom(typ, string(atom), column)
-}
-
-// Scan tokenizes an input string using a language-specific scanToken function.
-// The scanToken function is called repeatedly until the input is exhausted.
-// It returns nil (no token, no error) for skippable input like whitespace.
-// Errors are accumulated and returned joined at the end.
-func Scan[T Type](input string, scanToken func(*iterator.Iterator[rune]) (*Token[T], error)) ([]Token[T], error) {
-	i := iterator.Of([]rune(input))
-	tokens := []Token[T]{}
-	errorList := []error{}
-
-	for !i.Done() {
-		token, err := scanToken(i)
-		if err != nil {
-			errorList = append(errorList, err)
-		} else if token != nil {
-			tokens = append(tokens, *token)
-		}
-	}
-
-	return tokens, errors.Join(errorList...)
-}

pkg/token/token.go

@@ -1,36 +0,0 @@
-// Package token provides generic token types and scanning/parsing primitives
-// for building language-specific lexers and parsers.
-package token
-
-// A Type is a constraint for language-specific token type enums.
-// It must be comparable (for equality checks) and must have a Name method
-// that returns a human-readable string for error messages.
-type Type interface {
-	comparable
-	// Name returns a human-readable name for this token type.
-	Name() string
-}
-
-// A Token is a lexical unit in a source language.
-type Token[T Type] struct {
-	Column int    // Where the token begins in the source text.
-	Type   T      // What type the token is.
-	Value  string // The value of the token.
-}
-
-// New creates a Token of the given type at the given column.
-// The token's value is derived from its type's Name method.
-func New[T Type](typ T, column int) *Token[T] {
-	return &Token[T]{Type: typ, Column: column, Value: typ.Name()}
-}
-
-// NewAtom creates a Token of the given type with a custom value at the given
-// column.
-func NewAtom[T Type](typ T, name string, column int) *Token[T] {
-	return &Token[T]{Type: typ, Column: column, Value: name}
-}
-
-// Name returns the type of the Token, as a string.
-func (t Token[T]) Name() string {
-	return t.Type.Name()
-}

pkg/trace/trace.go

@@ -0,0 +1,25 @@
+package trace
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+func Indent(s string, size int) string {
+	lines := strings.Lines(s)
+	indent := strings.Repeat(" ", size)
+
+	indented := ""
+	for line := range lines {
+		indented += indent + line
+	}
+
+	return indented
+}
+
+func Wrap(child error, format string, a ...any) error {
+	parent := fmt.Errorf(format, a...)
+	childErrString := Indent(child.Error(), 4)
+	return errors.New(parent.Error() + "\n" + childErrString)
+}