cmd/lambda/lambda.go

@@ -1,16 +1,24 @@
 package main
 
 import (
+	"fmt"
 	"os"
 
-	"git.maximhutz.com/max/lambda/internal/cli"
 	"git.maximhutz.com/max/lambda/internal/config"
+	"github.com/spf13/cobra"
 )
 
-func main() {
-	// Parse CLI arguments.
+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, args []string) error {
+			// Legacy behavior when no subcommand is given.
 			options, err := config.FromArgs()
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 
 			logger := options.GetLogger()
 			logger.Info("using program arguments", "args", os.Args)
@@ -20,36 +28,67 @@ func main() {
 
 			// Get input.
 			input, err := options.Source.Extract()
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 
 			// Parse code into syntax tree.
 			repr, err := r.Unmarshal(input, "saccharine")
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 			logger.Info("parsed syntax tree", "tree", repr)
 
 			// Compile expression to lambda calculus.
 			compiled, err := r.ConvertTo(repr, "lambda")
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 			logger.Info("compiled λ expression", "tree", compiled)
 
 			// Create reducer with the compiled expression.
 			engine, err := r.GetDefaultEngine("lambda")
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 
 			process := engine.Load()
 			err = process.Set(compiled)
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
+
 			// Run reduction.
 			for process.Step(1) {
 			}
 
 			// Return the final reduced result.
 			result, err := process.Get()
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 
 			output, err := r.Marshal(result)
-	cli.HandleError(err)
+			if err != nil {
+				return err
+			}
 
-	err = options.Destination.Write(output)
-	cli.HandleError(err)
+			return options.Destination.Write(output)
+		},
+	}
+
+	cmd.PersistentFlags().BoolP("verbose", "v", false, "Enable verbose output")
+
+	cmd.AddCommand(LambdaConvert())
+	cmd.AddCommand(LambdaEngine())
+
+	return cmd
+}
+
+func main() {
+	lambda := Lambda()
+	if err := lambda.Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
 }

cmd/lambda/lambda_convert.go

@@ -0,0 +1,100 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"git.maximhutz.com/max/lambda/internal/cli"
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+)
+
+// inferReprFromPath returns the repr type based on file extension.
+func inferReprFromPath(path string) (string, error) {
+	switch ext := strings.ToLower(filepath.Ext(path)); ext {
+	case ".lam", ".lambda":
+		return "lambda", nil
+	case ".sac", ".saccharine":
+		return "saccharine", nil
+	default:
+		return "", fmt.Errorf("unknown file extension '%s'", ext)
+	}
+}
+
+func LambdaConvert() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "convert <input> <output>",
+		Short: "Convert between lambda calculus representations",
+		Args:  cobra.ExactArgs(2),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			inputPath := args[0]
+			outputPath := args[1]
+
+			// Infer repr types from extensions.
+			inputRepr, err := inferReprFromPath(inputPath)
+			if err != nil {
+				return fmt.Errorf("input file: %w", err)
+			}
+
+			outputRepr, err := inferReprFromPath(outputPath)
+			if 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)
+			}
+
+			if viper.GetBool("verbose") {
+				fmt.Fprintf(os.Stderr, "Parsed %s from %s\n", inputRepr, inputPath)
+			}
+
+			// Convert to output repr if different.
+			var result cli.Repr
+			if inputRepr != outputRepr {
+				result, err = r.ConvertTo(repr, outputRepr)
+				if err != nil {
+					return fmt.Errorf("converting %s to %s: %w", inputRepr, outputRepr, err)
+				}
+
+				if viper.GetBool("verbose") {
+					fmt.Fprintf(os.Stderr, "Converted to %s\n", outputRepr)
+				}
+			} else {
+				result = repr
+			}
+
+			// Marshal output.
+			output, err := r.Marshal(result)
+			if err != nil {
+				return fmt.Errorf("marshaling output: %w", err)
+			}
+
+			// Write output file.
+			err = os.WriteFile(outputPath, []byte(output), 0644)
+			if err != nil {
+				return fmt.Errorf("writing output file: %w", err)
+			}
+
+			if viper.GetBool("verbose") {
+				fmt.Fprintf(os.Stderr, "Wrote %s to %s\n", outputRepr, outputPath)
+			}
+
+			return nil
+		},
+	}
+
+	return cmd
+}

cmd/lambda/lambda_engine.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"github.com/spf13/cobra"
+)
+
+func LambdaEngine() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "engine",
+		Short: "Information about available engines",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return cmd.Help()
+		},
+	}
+
+	cmd.AddCommand(LambdaEngineList())
+
+	return cmd
+}

cmd/lambda/lambda_engine_list.go

@@ -0,0 +1,26 @@
+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(cmd *cobra.Command, args []string) error {
+			r := GetRegistry()
+
+			for engine := range r.ListEngines() {
+				fmt.Println(engine.Name())
+			}
+
+			return nil
+		},
+	}
+
+	return cmd
+}

go.mod

@@ -6,6 +6,21 @@ require github.com/stretchr/testify v1.11.1
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
+	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/sagikazarmark/locafero v0.11.0 // indirect
+	github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 // indirect
+	github.com/spf13/afero v1.15.0 // indirect
+	github.com/spf13/cast v1.10.0 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.10 // indirect
+	github.com/spf13/viper v1.21.0 // indirect
+	github.com/subosito/gotenv v1.6.0 // indirect
+	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/sys v0.29.0 // indirect
+	golang.org/x/text v0.28.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,9 +1,42 @@
+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/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
+github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
+github.com/go-viper/mapstructure/v2 v2.4.0 h1:EBsztssimR/CONLSZZ04E8qAkxNYq4Qp9LvH92wZUgs=
+github.com/go-viper/mapstructure/v2 v2.4.0/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
+github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 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/sagikazarmark/locafero v0.11.0 h1:1iurJgmM9G3PA/I+wWYIOw/5SyBtxapeHDcg+AAIFXc=
+github.com/sagikazarmark/locafero v0.11.0/go.mod h1:nVIGvgyzw595SUSUE6tvCp3YYTeHs15MvlmU87WwIik=
+github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 h1:+jumHNA0Wrelhe64i8F6HNlS8pkoyMv5sreGx2Ry5Rw=
+github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8/go.mod h1:3n1Cwaq1E1/1lhQhtRK2ts/ZwZEhjcQeJQ1RuC6Q/8U=
+github.com/spf13/afero v1.15.0 h1:b/YBCLWAJdFWJTN9cLhiXXcD7mzKn9Dm86dNnfyQw1I=
+github.com/spf13/afero v1.15.0/go.mod h1:NC2ByUVxtQs4b3sIUphxK0NioZnmxgyCrfzeuq8lxMg=
+github.com/spf13/cast v1.10.0 h1:h2x0u2shc1QuLHfxi+cTJvs30+ZAHOGRic8uyGTDWxY=
+github.com/spf13/cast v1.10.0/go.mod h1:jNfB8QC9IA6ZuY2ZjDp0KtFO2LZZlg4S/7bzP6qqeHo=
+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/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
+github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/spf13/viper v1.21.0 h1:x5S+0EU27Lbphp4UKm1C+1oQO+rKx36vfCoaVebLFSU=
+github.com/spf13/viper v1.21.0/go.mod h1:P0lhsswPGWD/1lZJ9ny3fYnVqxiegrlNrEmgLjbTCAY=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/subosito/gotenv v1.6.0 h1:9NlTDc1FTs4qu0DDq7AEtTPNw6SVm7uBMsUCUjABIf8=
+github.com/subosito/gotenv v1.6.0/go.mod h1:Dk4QP5c2W3ibzajGcXpNraDfq2IrhjMIvMSWPKKo0FU=
+go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
+go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+golang.org/x/sys v0.29.0 h1:TPYlXGxvx1MGTn2GiZDhnjPA9wZzZeGKHHmKhHYvgaU=
+golang.org/x/sys v0.29.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/text v0.28.0 h1:rhazDwis8INMIwQ4tpjLDzUhx6RlXqZNPEM0huQojng=
+golang.org/x/text v0.28.0/go.mod h1:U8nCwOR8jO/marOQ0QbDiOngZVEBB7MAiitBuMjXiNU=
 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/exit.go

@@ -1,18 +0,0 @@
-// Package "cli" provides miscellaneous helper functions.
-package cli
-
-import (
-	"fmt"
-	"os"
-)
-
-// A helper function to handle errors in the program. If it is given an error,
-// the program will exist, and print the error.
-func HandleError(err error) {
-	if err == nil {
-		return
-	}
-
-	fmt.Fprintln(os.Stderr, "ERROR:", err)
-	os.Exit(1)
-}

internal/registry/registry.go

@@ -2,6 +2,8 @@ package registry
 
 import (
 	"fmt"
+	"iter"
+	"maps"
 
 	"git.maximhutz.com/max/lambda/internal/cli"
 )
@@ -63,7 +65,7 @@ func (r *Registry) MustAddEngine(e cli.Engine) {
 	}
 }
 
-func (r *Registry) GetEngine(name string) (cli.Engine, error) {
+func (r Registry) GetEngine(name string) (cli.Engine, error) {
 	e, ok := r.engines[name]
 	if !ok {
 		return nil, fmt.Errorf("engine '%s' not found", name)
@@ -72,6 +74,10 @@ func (r *Registry) GetEngine(name string) (cli.Engine, error) {
 	return e, nil
 }
 
+func (r Registry) ListEngines() iter.Seq[cli.Engine] {
+	return maps.Values(r.engines)
+}
+
 func (r *Registry) GetDefaultEngine(id string) (cli.Engine, error) {
 	for _, engine := range r.engines {
 		if engine.InType() == id {