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docs: document remaining packages and simplify AST types (#45)

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## Summary

- Added doc comments across the codebase: `pkg/lambda`, `pkg/saccharine`, `pkg/codec`, `pkg/engine`, `pkg/iterator`, `pkg/set`, `pkg/convert`, `internal/registry`, and `cmd/lambda`.
- Made lambda and saccharine expression structs use public fields instead of getters, matching `go/ast` conventions.
- Removed superfluous constructors for saccharine and lambda expression/statement types in favor of struct literals.
- Consolidated saccharine token constructors into a single `NewToken` function.
- Removed the unused `trace` package.

## Test plan

- [x] `go build ./...` passes.
- [x] `go test ./...` passes.
- [ ] Verify `go doc` output renders correctly for documented packages.

Reviewed-on: #45
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
This commit was merged in pull request #45.
This commit is contained in:
Maxim Hutz
2026-02-10 01:15:41 +00:00
committed by Maxim Hutz
parent 1f486875fd
commit 361f529bdc
33 changed files with 506 additions and 463 deletions
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1
cmd/lambda/lambda.go
View File

@@ -1,3 +1,4 @@
// Package main defines the 'lambda' command-line interface (CLI).
package main
import (

2
cmd/lambda/lambda_engine.go
View File

@@ -9,7 +9,7 @@ func LambdaEngine() *cobra.Command {
Use: "engine",
Aliases: []string{"eng"},
Short: "Information about available engines",
RunE: func(cmd *cobra.Command, args []string) error {
RunE: func(cmd *cobra.Command, _ []string) error {
return cmd.Help()
},
}

2
cmd/lambda/lambda_engine_list.go
View File

@@ -11,7 +11,7 @@ func LambdaEngineList() *cobra.Command {
Use: "list",
Aliases: []string{"ls"},
Short: "List available engines",
RunE: func(cmd *cobra.Command, args []string) error {
RunE: func(*cobra.Command, []string) error {
r := GetRegistry()
for engine := range r.ListEngines() {

4
cmd/lambda/registry.go
View File

@@ -19,8 +19,8 @@ func GetRegistry() *registry.Registry {
(registry.RegisterEngine(r, normalorder.NewProcess, "normalorder", "lambda"))
// Marshalers
(registry.RegisterCodec(r, lambda.Marshaler{}, "lambda"))
(registry.RegisterCodec(r, saccharine.Marshaler{}, "saccharine"))
(registry.RegisterCodec(r, lambda.Codec{}, "lambda"))
(registry.RegisterCodec(r, saccharine.Codec{}, "saccharine"))
return r
}

18
internal/registry/codec.go
View File

@@ -7,18 +7,24 @@ import (
"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
}
type convertedCodec[T any] struct {
// 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 convertedCodec[T]) Decode(s string) (Expr, error) {
func (c registeredCodec[T]) Decode(s string) (Expr, error) {
t, err := c.codec.Decode(s)
if err != nil {
return nil, err
@@ -27,7 +33,7 @@ func (c convertedCodec[T]) Decode(s string) (Expr, error) {
return NewExpr(c.inType, t), nil
}
func (c convertedCodec[T]) Encode(r Expr) (string, error) {
func (c registeredCodec[T]) Encode(r Expr) (string, error) {
t, ok := r.Data().(T)
if !ok {
dataType := reflect.TypeOf(r.Data())
@@ -38,13 +44,15 @@ func (c convertedCodec[T]) Encode(r Expr) (string, error) {
return c.codec.Encode(t)
}
func (c convertedCodec[T]) InType() string { return c.inType }
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] = convertedCodec[T]{m, inType}
registry.codecs[inType] = registeredCodec[T]{m, inType}
return nil
}

28
internal/registry/conversion.go
View File

@@ -6,19 +6,29 @@ import (
"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)
}
type convertedConversion[T, U any] struct {
// 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 convertedConversion[T, U]) Run(expr Expr) (Expr, error) {
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)
@@ -32,12 +42,18 @@ func (c convertedConversion[T, U]) Run(expr Expr) (Expr, error) {
return NewExpr(c.outType, u), nil
}
func (c convertedConversion[T, U]) InType() string { return c.inType }
func (c registeredConversion[T, U]) InType() string { return c.inType }
func (c convertedConversion[T, U]) OutType() string { return c.outType }
func (c registeredConversion[T, U]) OutType() string { return c.outType }
func RegisterConversion[T, U any](registry *Registry, conversion func(T) (U, error), inType, outType string) error {
registry.converter.Add(convertedConversion[T, U]{conversion, inType, 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
}

7
internal/registry/converter.go
View File

@@ -1,13 +1,18 @@
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 {
@@ -18,6 +23,8 @@ func (g *Converter) Add(c Conversion) {
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]
}

26
internal/registry/engine.go
View File

@@ -6,26 +6,36 @@ import (
"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
}
type convertedEngine[T any] struct {
// 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 convertedEngine[T]) InType() string { return e.inType }
func (e registeredEngine[T]) InType() string { return e.inType }
func (e convertedEngine[T]) Name() string { return e.name }
func (e registeredEngine[T]) Name() string { return e.name }
func (e convertedEngine[T]) Load(expr Expr) (Process, error) {
func (e registeredEngine[T]) Load(expr Expr) (Process, error) {
t, ok := expr.Data().(T)
if !ok {
return nil, fmt.Errorf("'ncorrent format '%s' for engine '%s'", expr.Repr(), e.inType)
return nil, fmt.Errorf("incorrect format '%s' for engine '%s'", expr.Repr(), e.inType)
}
process, err := e.engine(t)
@@ -33,14 +43,16 @@ func (e convertedEngine[T]) Load(expr Expr) (Process, error) {
return nil, err
}
return convertedProcess[T]{process, e.inType}, nil
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] = &convertedEngine[T]{e, name, inType}
registry.engines[name] = &registeredEngine[T]{e, name, inType}
return nil
}

16
internal/registry/expr.go
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@@ -1,24 +1,26 @@
package registry
// A Expr is a lambda calculus expression. It can have any type of
// Expresentation, so long as that class is known to the registry it is handled
// 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 Expresentation. It is assumed if
// two expressions have the same Repr(), they have the same Expresentation.
// Repr returns the name of the underlying representation. Two expressions
// with the same Repr() are assumed to have the same representation type.
Repr() string
// The base expression data.
// Data returns the underlying expression data.
Data() any
}
// A baseExpr is the default implementation of Expr.
type baseExpr struct {
id string
data any
}
func (r baseExpr) Repr() string { return r.id }
func (e baseExpr) Repr() string { return e.id }
func (r baseExpr) Data() any { return r.data }
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} }

18
internal/registry/process.go
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@@ -4,28 +4,32 @@ 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
}
type convertedProcess[T any] struct {
// 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 (e convertedProcess[T]) InType() string { return e.inType }
func (p registeredProcess[T]) InType() string { return p.inType }
func (b convertedProcess[T]) Get() (Expr, error) {
s, err := b.process.Get()
func (p registeredProcess[T]) Get() (Expr, error) {
s, err := p.process.Get()
if err != nil {
return nil, err
}
return NewExpr(b.inType, s), nil
return NewExpr(p.inType, s), nil
}
func (b convertedProcess[T]) Step(i int) bool {
return b.process.Step(i)
func (p registeredProcess[T]) Step(i int) bool {
return p.process.Step(i)
}

23
internal/registry/registry.go
View File

@@ -1,3 +1,5 @@
// Package registry defines a structure to hold all available representations,
// engines, and conversions between them.
package registry
import (
@@ -6,12 +8,15 @@ import (
"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{},
@@ -20,6 +25,8 @@ func New() *Registry {
}
}
// 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 {
@@ -29,10 +36,13 @@ func (r Registry) GetEngine(name string) (Engine, error) {
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 {
@@ -45,6 +55,12 @@ func (r *Registry) GetDefaultEngine(id string) (Engine, error) {
// 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 {
@@ -62,6 +78,8 @@ func (r *Registry) ConvertTo(expr Expr, outType string) (Expr, error) {
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 {
@@ -71,6 +89,8 @@ func (r *Registry) Marshal(expr Expr) (string, error) {
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 {
@@ -94,6 +114,9 @@ func reverse[T any](list []T) []T {
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}

12
pkg/codec/codec.go
View File

@@ -1,8 +1,20 @@
// 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)
}

47
pkg/convert/saccharine_to_lambda.go
View File

@@ -1,3 +1,5 @@
// Package convert defined some standard conversions between various types of
// representations.
package convert
import (
@@ -8,7 +10,7 @@ import (
)
func encodeAtom(n *saccharine.Atom) lambda.Expression {
return lambda.NewVariable(n.Name)
return lambda.Variable{Name: n.Name}
}
func encodeAbstraction(n *saccharine.Abstraction) lambda.Expression {
@@ -19,13 +21,13 @@ func encodeAbstraction(n *saccharine.Abstraction) lambda.Expression {
// 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 := result.GetFree()
freeVars := lambda.GetFree(result)
freshName := lambda.GenerateFreshName(freeVars)
parameters = append(parameters, freshName)
}
for i := len(parameters) - 1; i >= 0; i-- {
result = lambda.NewAbstraction(parameters[i], result)
result = lambda.Abstraction{Parameter: parameters[i], Body: result}
}
return result
@@ -41,7 +43,7 @@ func encodeApplication(n *saccharine.Application) lambda.Expression {
}
for _, argument := range arguments {
result = lambda.NewApplication(result, argument)
result = lambda.Application{Abstraction: result, Argument: argument}
}
return result
@@ -53,22 +55,22 @@ func reduceLet(s *saccharine.LetStatement, e lambda.Expression) lambda.Expressio
if len(s.Parameters) == 0 {
value = encodeExpression(s.Body)
} else {
value = encodeAbstraction(saccharine.NewAbstraction(s.Parameters, s.Body))
value = encodeAbstraction(&saccharine.Abstraction{Parameters: s.Parameters, Body: s.Body})
}
return lambda.NewApplication(
lambda.NewAbstraction(s.Name, e),
value,
)
return lambda.Application{
Abstraction: lambda.Abstraction{Parameter: s.Name, Body: e},
Argument: value,
}
}
func reduceDeclare(s *saccharine.DeclareStatement, e lambda.Expression) lambda.Expression {
freshVar := lambda.GenerateFreshName(e.GetFree())
freshVar := lambda.GenerateFreshName(lambda.GetFree(e))
return lambda.NewApplication(
lambda.NewAbstraction(freshVar, e),
encodeExpression(s.Value),
)
return lambda.Application{
Abstraction: lambda.Abstraction{Parameter: freshVar, Body: e},
Argument: encodeExpression(s.Value),
}
}
func reduceStatement(s saccharine.Statement, e lambda.Expression) lambda.Expression {
@@ -110,24 +112,27 @@ func encodeExpression(s saccharine.Expression) lambda.Expression {
func decodeExression(l lambda.Expression) saccharine.Expression {
switch l := l.(type) {
case lambda.Variable:
return saccharine.NewAtom(l.Name())
return &saccharine.Atom{Name: l.Name}
case lambda.Abstraction:
return saccharine.NewAbstraction(
[]string{l.Parameter()},
decodeExression(l.Body()))
return &saccharine.Abstraction{
Parameters: []string{l.Parameter},
Body: decodeExression(l.Body)}
case lambda.Application:
return saccharine.NewApplication(
decodeExression(l.Abstraction()),
[]saccharine.Expression{decodeExression(l.Argument())})
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
}

10
pkg/engine/engine.go
View File

@@ -2,11 +2,17 @@
// expression.
package engine
// A Process handles the reduction of a
// A Process handles the reduction of a single expression.
type Process[T any] interface {
// 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
// defined is less than zero, it will perform as many reductions as
// possible. Returns whether a reduction was performed.
Step(int) bool
}
// An Engine is an object that handles
// An Engine is an function that generates reduction processes.
type Engine[T any] = func(T) (Process[T], error)

16
pkg/engine/normalorder/reduce_once.go
View File

@@ -10,25 +10,25 @@ import "git.maximhutz.com/max/lambda/pkg/lambda"
func ReduceOnce(e lambda.Expression) (lambda.Expression, bool) {
switch e := e.(type) {
case lambda.Abstraction:
body, reduced := ReduceOnce(e.Body())
body, reduced := ReduceOnce(e.Body)
if reduced {
return lambda.NewAbstraction(e.Parameter(), body), true
return lambda.Abstraction{Parameter: e.Parameter, Body: body}, true
}
return e, false
case lambda.Application:
if fn, fnOk := e.Abstraction().(lambda.Abstraction); fnOk {
return fn.Body().Substitute(fn.Parameter(), e.Argument()), true
if fn, fnOk := e.Abstraction.(lambda.Abstraction); fnOk {
return lambda.Substitute(fn.Body, fn.Parameter, e.Argument), true
}
abs, reduced := ReduceOnce(e.Abstraction())
abs, reduced := ReduceOnce(e.Abstraction)
if reduced {
return lambda.NewApplication(abs, e.Argument()), true
return lambda.Application{Abstraction: abs, Argument: e.Argument}, true
}
arg, reduced := ReduceOnce(e.Argument())
arg, reduced := ReduceOnce(e.Argument)
if reduced {
return lambda.NewApplication(e.Abstraction(), arg), true
return lambda.Application{Abstraction: e.Abstraction, Argument: arg}, true
}
return e, false

30
pkg/iterator/iterator.go
View File

@@ -1,35 +1,37 @@
/*
Package "iterator"
*/
// Package iterator defines a generic way to iterator over a slice of data.
package iterator
import "fmt"
// An iterator over slices.
// An Iterator traverses over slices.
type Iterator[T any] struct {
items []T
index int
}
// Create a new iterator, over a set of items.
// Of creates a new iterator, over a set of defined items.
func Of[T any](items []T) *Iterator[T] {
return &Iterator[T]{items: items, index: 0}
}
// Returns the current position of the iterator.
// Index returns the current position of the iterator.
func (i Iterator[T]) Index() int {
return i.index
}
// Copy returns a identical clone of the iterator. The underlying data structure
// is not cloned.
func (i Iterator[T]) Copy() *Iterator[T] {
return &Iterator[T]{items: i.items, index: i.index}
}
// Sync returns the iterator to the position of another. It is assumed that the
// iterators both operate on the same set of data.
func (i *Iterator[T]) Sync(o *Iterator[T]) {
i.index = o.index
}
// Create a new iterator, over a set of items.
// Get returns the datum at the current position of the iterator.
func (i Iterator[T]) Get() (T, error) {
var null T
if i.Done() {
@@ -39,6 +41,7 @@ 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 {
var null T
if i.Done() {
@@ -48,13 +51,16 @@ func (i Iterator[T]) MustGet() 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++
}
}
// Create a new iterator, over a set of items.
// Next attempts to increment the iterator. Returns an error if it cannot be
// incremented.
func (i *Iterator[T]) Next() (T, error) {
item, err := i.Get()
if err == nil {
@@ -64,16 +70,20 @@ func (i *Iterator[T]) Next() (T, error) {
return item, err
}
// Create a new iterator, over a set of items.
// Back decrements the iterator. If the iterator is already at the beginning of
// the slice, this is a no-op.
func (i *Iterator[T]) Back() {
i.index = max(i.index-1, 0)
}
// Returns the current position of the iterator.
// Done returns whether the iterator is at the end of the slice or not.
func (i Iterator[T]) Done() bool {
return i.index == len(i.items)
}
// Do attempts to perform an operation using the iterator. If the operation
// succeeds, the iterator is updated. If the operation fails, the iterator is
// rolled back, and an error is returned.
func Do[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
i2 := i.Copy()

16
pkg/lambda/codec.go
View File

@@ -6,14 +6,20 @@ import (
"git.maximhutz.com/max/lambda/pkg/codec"
)
type Marshaler struct{}
// A Codec is a [codec.Codec] that serializes lambda calculus expressions.
// Decode is not implemented and always returns an error.
// Encode stringifies an expression using standard lambda notation.
type Codec struct{}
func (m Marshaler) Decode(string) (Expression, error) {
// Decode parses a string as lambda calculus. Returns an error if it cannot.
func (m Codec) Decode(string) (Expression, error) {
return nil, fmt.Errorf("unimplemented")
}
func (m Marshaler) Encode(e Expression) (string, error) {
return e.String(), nil
// 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] = (*Marshaler)(nil)
var _ codec.Codec[Expression] = (*Codec)(nil)

100
pkg/lambda/expression.go
View File

@@ -1,100 +0,0 @@
package lambda
import (
"fmt"
"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 {
fmt.Stringer
// 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
}
/** ------------------------------------------------------------------------- */
type Abstraction struct {
parameter string
body Expression
}
var _ Expression = Abstraction{}
func (a Abstraction) Parameter() string {
return a.parameter
}
func (a Abstraction) Body() Expression {
return a.body
}
func (a Abstraction) String() string {
return "\\" + a.parameter + "." + a.body.String()
}
func NewAbstraction(parameter string, body Expression) Abstraction {
return Abstraction{parameter, body}
}
/** ------------------------------------------------------------------------- */
type Application struct {
abstraction Expression
argument Expression
}
var _ Expression = Application{}
func (a Application) Abstraction() Expression {
return a.abstraction
}
func (a Application) Argument() Expression {
return a.argument
}
func (a Application) String() string {
return "(" + a.abstraction.String() + " " + a.argument.String() + ")"
}
func NewApplication(abstraction Expression, argument Expression) Application {
return Application{abstraction, argument}
}
/** ------------------------------------------------------------------------- */
type Variable struct {
name string
}
var _ Expression = Variable{}
func (v Variable) Name() string {
return v.name
}
func (v Variable) String() string {
return v.name
}
func NewVariable(name string) Variable {
return Variable{name}
}

32
pkg/lambda/get_free_variables.go
View File

@@ -1,19 +1,27 @@
package lambda
import "git.maximhutz.com/max/lambda/pkg/set"
import (
"fmt"
func (e Variable) GetFree() set.Set[string] {
return set.New(e.Name())
}
"git.maximhutz.com/max/lambda/pkg/set"
)
func (e Abstraction) GetFree() set.Set[string] {
vars := e.Body().GetFree()
vars.Remove(e.Parameter())
// 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
}
func (e Application) GetFree() set.Set[string] {
vars := e.Abstraction().GetFree()
vars.Merge(e.Argument().GetFree())
case Application:
vars := GetFree(e.Abstraction)
vars.Merge(GetFree(e.Argument))
return vars
default:
panic(fmt.Errorf("unknown expression type: %v", e))
}
}

22
pkg/lambda/is_free_variable.go
View File

@@ -1,12 +1,18 @@
package lambda
func (e Variable) IsFree(n string) bool {
return e.Name() == n
}
import "fmt"
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)
// 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))
}
}

31
pkg/lambda/lambda.go Normal file
View File

@@ -0,0 +1,31 @@
// 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() {}

37
pkg/lambda/rename.go
View File

@@ -1,28 +1,31 @@
package lambda
import "fmt"
// 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)
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
}
func (e Abstraction) Rename(target string, newName string) Expression {
newParam := e.Parameter()
if e.Parameter() == target {
case Abstraction:
newParam := e.Parameter
if e.Parameter == target {
newParam = newName
}
newBody := e.Body().Rename(target, newName)
newBody := Rename(e.Body, 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)
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))
}
}

17
pkg/lambda/stringify.go Normal file
View File

@@ -0,0 +1,17 @@
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))
}
}

46
pkg/lambda/substitute.go
View File

@@ -1,35 +1,41 @@
package lambda
func (e Variable) Substitute(target string, replacement Expression) Expression {
if e.Name() == target {
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
}
func (e Abstraction) Substitute(target string, replacement Expression) Expression {
if e.Parameter() == target {
case Abstraction:
if e.Parameter == target {
return e
}
body := e.Body()
param := e.Parameter()
if replacement.IsFree(param) {
freeVars := replacement.GetFree()
freeVars.Merge(body.GetFree())
body := e.Body
param := e.Parameter
if IsFree(replacement, param) {
freeVars := GetFree(replacement)
freeVars.Merge(GetFree(body))
freshVar := GenerateFreshName(freeVars)
body = body.Rename(param, freshVar)
body = Rename(body, param, freshVar)
param = freshVar
}
newBody := body.Substitute(target, replacement)
return NewAbstraction(param, newBody)
}
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)
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)
return Application{Abstraction: abs, Argument: arg}
default:
panic(fmt.Errorf("unknown expression type: %v", e))
}
}

15
pkg/saccharine/codec.go
View File

@@ -1,14 +1,15 @@
// Package "saccharine" provides a simple language built on top of λ-calculus,
// to facilitate productive coding using it.
package saccharine
import (
"git.maximhutz.com/max/lambda/pkg/codec"
)
type Marshaler struct{}
// A Codec is a [codec.Codec] that serializes Saccharine expressions.
type Codec struct{}
func (m Marshaler) Decode(s string) (Expression, error) {
// 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
@@ -17,8 +18,10 @@ func (m Marshaler) Decode(s string) (Expression, error) {
return parse(tokens)
}
func (m Marshaler) Encode(e Expression) (string, error) {
// 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] = (*Marshaler)(nil)
var _ codec.Codec[Expression] = (*Codec)(nil)

49
pkg/saccharine/expression.go
View File

@@ -1,49 +0,0 @@
package saccharine
type Expression interface {
IsExpression()
}
/** ------------------------------------------------------------------------- */
type Abstraction struct {
Parameters []string
Body Expression
}
type Application struct {
Abstraction Expression
Arguments []Expression
}
type Atom struct {
Name string
}
type Clause struct {
Statements []Statement
Returns Expression
}
func (Abstraction) IsExpression() {}
func (Application) IsExpression() {}
func (Atom) IsExpression() {}
func (Clause) IsExpression() {}
/** ------------------------------------------------------------------------- */
func NewAbstraction(parameter []string, body Expression) *Abstraction {
return &Abstraction{Parameters: parameter, Body: body}
}
func NewApplication(abstraction Expression, arguments []Expression) *Application {
return &Application{Abstraction: abstraction, Arguments: arguments}
}
func NewAtom(name string) *Atom {
return &Atom{Name: name}
}
func NewClause(statements []Statement, returns Expression) *Clause {
return &Clause{Statements: statements, Returns: returns}
}

71
pkg/saccharine/parse.go
View File

@@ -5,13 +5,12 @@ import (
"fmt"
"git.maximhutz.com/max/lambda/pkg/iterator"
"git.maximhutz.com/max/lambda/pkg/trace"
)
type TokenIterator = iterator.Iterator[Token]
type tokenIterator = iterator.Iterator[Token]
func parseRawToken(i *TokenIterator, expected TokenType) (*Token, error) {
return iterator.Do(i, func(i *TokenIterator) (*Token, error) {
func parseRawToken(i *tokenIterator, expected TokenType) (*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 {
@@ -22,7 +21,7 @@ func parseRawToken(i *TokenIterator, expected TokenType) (*Token, error) {
})
}
func passSoftBreaks(i *TokenIterator) {
func passSoftBreaks(i *tokenIterator) {
for {
if _, err := parseRawToken(i, TokenSoftBreak); err != nil {
return
@@ -30,8 +29,8 @@ func passSoftBreaks(i *TokenIterator) {
}
}
func parseToken(i *TokenIterator, expected TokenType, ignoreSoftBreaks bool) (*Token, error) {
return iterator.Do(i, func(i *TokenIterator) (*Token, error) {
func parseToken(i *tokenIterator, expected TokenType, ignoreSoftBreaks bool) (*Token, error) {
return iterator.Do(i, func(i *tokenIterator) (*Token, error) {
if ignoreSoftBreaks {
passSoftBreaks(i)
}
@@ -40,15 +39,15 @@ func parseToken(i *TokenIterator, expected TokenType, ignoreSoftBreaks bool) (*T
})
}
func parseString(i *TokenIterator) (string, error) {
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())
return "", fmt.Errorf("no variable (col %d): %w", i.Index(), err)
} else {
return tok.Value, nil
}
}
func parseBreak(i *TokenIterator) (*Token, error) {
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 {
@@ -58,13 +57,13 @@ func parseBreak(i *TokenIterator) (*Token, error) {
}
}
func parseList[U any](i *TokenIterator, fn func(*TokenIterator) (U, error), minimum int) ([]U, error) {
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 nil, fmt.Errorf("expected at least '%v' items, got only '%v': %w", minimum, len(results), err)
}
return results, nil
} else {
@@ -73,45 +72,45 @@ func parseList[U any](i *TokenIterator, fn func(*TokenIterator) (U, error), mini
}
}
func parseAbstraction(i *TokenIterator) (*Abstraction, error) {
return iterator.Do(i, func(i *TokenIterator) (*Abstraction, error) {
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)
return nil, fmt.Errorf("no function slash (col %d): %w", i.MustGet().Column, err)
} 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)
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 NewAbstraction(parameters, body), nil
return &Abstraction{Parameters: parameters, Body: body}, nil
}
})
}
func parseApplication(i *TokenIterator) (*Application, error) {
return iterator.Do(i, func(i *TokenIterator) (*Application, error) {
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)
return nil, fmt.Errorf("no openning brackets (col %d): %w", i.MustGet().Column, err)
} 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)
return nil, fmt.Errorf("no closing brackets (col %d): %w", i.MustGet().Column, err)
} else {
return NewApplication(expressions[0], expressions[1:]), nil
return &Application{Abstraction: expressions[0], Arguments: expressions[1:]}, nil
}
})
}
func parseAtom(i *TokenIterator) (*Atom, error) {
func parseAtom(i *tokenIterator) (*Atom, error) {
if tok, err := parseToken(i, TokenAtom, true); err != nil {
return nil, trace.Wrap(err, "no variable (col %d)", i.Index())
return nil, fmt.Errorf("no variable (col %d): %w", i.Index(), err)
} else {
return NewAtom(tok.Value), nil
return &Atom{Name: tok.Value}, nil
}
}
func parseStatements(i *TokenIterator) ([]Statement, error) {
func parseStatements(i *tokenIterator) ([]Statement, error) {
statements := []Statement{}
//nolint:errcheck
@@ -130,7 +129,7 @@ func parseStatements(i *TokenIterator) ([]Statement, error) {
return statements, nil
}
func parseClause(i *TokenIterator, braces bool) (*Clause, error) {
func parseClause(i *tokenIterator, braces bool) (*Clause, error) {
if braces {
if _, err := parseToken(i, TokenOpenBrace, true); err != nil {
return nil, err
@@ -156,11 +155,11 @@ func parseClause(i *TokenIterator, braces bool) (*Clause, error) {
}
}
return NewClause(stmts[:len(stmts)-1], last.Value), nil
return &Clause{Statements: stmts[:len(stmts)-1], Returns: last.Value}, nil
}
func parseExpression(i *TokenIterator) (Expression, error) {
return iterator.Do(i, func(i *TokenIterator) (Expression, error) {
func parseExpression(i *tokenIterator) (Expression, error) {
return iterator.Do(i, func(i *tokenIterator) (Expression, error) {
passSoftBreaks(i)
switch peek := i.MustGet(); peek.Type {
@@ -178,8 +177,8 @@ func parseExpression(i *TokenIterator) (Expression, error) {
})
}
func parseLet(i *TokenIterator) (*LetStatement, error) {
return iterator.Do(i, func(i *TokenIterator) (*LetStatement, error) {
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 {
@@ -187,20 +186,20 @@ func parseLet(i *TokenIterator) (*LetStatement, error) {
} else if body, err := parseExpression(i); err != nil {
return nil, err
} else {
return NewLet(parameters[0], parameters[1:], body), nil
return &LetStatement{Name: parameters[0], Parameters: parameters[1:], Body: body}, nil
}
})
}
func parseDeclare(i *TokenIterator) (*DeclareStatement, error) {
func parseDeclare(i *tokenIterator) (*DeclareStatement, error) {
if value, err := parseExpression(i); err != nil {
return nil, err
} else {
return NewDeclare(value), nil
return &DeclareStatement{Value: value}, nil
}
}
func parseStatement(i *TokenIterator) (Statement, error) {
func parseStatement(i *tokenIterator) (Statement, error) {
if let, letErr := parseLet(i); letErr == nil {
return let, nil
} else if declare, declErr := parseDeclare(i); declErr == nil {

60
pkg/saccharine/saccharine.go Normal file
View File

@@ -0,0 +1,60 @@
// 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() {}

23
pkg/saccharine/scan.go
View File

@@ -6,7 +6,6 @@ import (
"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.
@@ -51,38 +50,38 @@ func scanToken(i *iterator.Iterator[rune]) (*Token, error) {
letter, err := i.Next()
if err != nil {
return nil, trace.Wrap(err, "cannot produce next token")
return nil, fmt.Errorf("cannot produce next token: %w", err)
}
switch {
case letter == '(':
return NewTokenOpenParen(index), nil
return NewToken(TokenOpenParen, index), nil
case letter == ')':
return NewTokenCloseParen(index), nil
return NewToken(TokenCloseParen, index), nil
case letter == '.':
return NewTokenDot(index), nil
return NewToken(TokenDot, index), nil
case letter == '\\':
return NewTokenSlash(index), nil
return NewToken(TokenSlash, index), nil
case letter == '\n':
return NewTokenSoftBreak(index), nil
return NewToken(TokenSoftBreak, index), nil
case letter == '{':
return NewTokenOpenBrace(index), nil
return NewToken(TokenOpenBrace, index), nil
case letter == '}':
return NewTokenCloseBrace(index), nil
return NewToken(TokenCloseBrace, index), nil
case letter == ':':
if _, err := scanCharacter(i, '='); err != nil {
return nil, err
} else {
return NewTokenAssign(index), nil
return NewToken(TokenAssign, index), nil
}
case letter == ';':
return NewTokenHardBreak(index), nil
return NewToken(TokenHardBreak, 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")
return nil, fmt.Errorf("error while parsing comment: %w", err)
}
if r == '\n' {

30
pkg/saccharine/statement.go
View File

@@ -1,30 +0,0 @@
package saccharine
type Statement interface {
IsStatement()
}
/** ------------------------------------------------------------------------- */
type LetStatement struct {
Name string
Parameters []string
Body Expression
}
type DeclareStatement struct {
Value Expression
}
func (LetStatement) IsStatement() {}
func (DeclareStatement) IsStatement() {}
/** ------------------------------------------------------------------------- */
func NewLet(name string, parameters []string, body Expression) *LetStatement {
return &LetStatement{Name: name, Parameters: parameters, Body: body}
}
func NewDeclare(value Expression) *DeclareStatement {
return &DeclareStatement{Value: value}
}

90
pkg/saccharine/token.go
View File

@@ -2,90 +2,80 @@ package saccharine
import "fmt"
// All tokens in the pseudo-lambda language.
// A TokenType is an identifier for any token in the Saccharine language.
type TokenType int
// All official tokens of the Saccharine language.
const (
TokenOpenParen TokenType = 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.
// 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
)
// A representation of a token in source code.
// A Token in the Saccharine language.
type Token struct {
Column int // Where the token begins in the source text.
Type TokenType // What type the token is.
Value string // The value of the token.
}
func NewTokenOpenParen(column int) *Token {
return &Token{Type: TokenOpenParen, Column: column, Value: "("}
}
func NewTokenCloseParen(column int) *Token {
return &Token{Type: TokenCloseParen, Column: column, Value: ")"}
}
func NewTokenOpenBrace(column int) *Token {
return &Token{Type: TokenOpenBrace, Column: column, Value: "{"}
}
func NewTokenCloseBrace(column int) *Token {
return &Token{Type: TokenCloseBrace, Column: column, Value: "}"}
}
func NewTokenDot(column int) *Token {
return &Token{Type: TokenDot, Column: column, Value: "."}
}
func NewTokenHardBreak(column int) *Token {
return &Token{Type: TokenHardBreak, Column: column, Value: ";"}
}
func NewTokenAssign(column int) *Token {
return &Token{Type: TokenAssign, Column: column, Value: ":="}
}
func NewTokenSlash(column int) *Token {
return &Token{Type: TokenSlash, Column: column, Value: "\\"}
// NewToken creates a [Token] of the given type at the given column.
// The token's value is derived from its [TokenType].
func NewToken(typ TokenType, column int) *Token {
return &Token{Type: typ, Column: column, Value: typ.Name()}
}
// NewTokenAtom creates a [TokenAtom] with the given name at the given column.
func NewTokenAtom(name string, column int) *Token {
return &Token{Type: TokenAtom, Column: column, Value: name}
}
func NewTokenSoftBreak(column int) *Token {
return &Token{Type: TokenSoftBreak, Column: column, Value: "\\n"}
}
// 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 TokenAtom:
return "ATOM"
case TokenSoftBreak:
return "\\n"
case TokenHardBreak:
return ";"
default:
panic(fmt.Errorf("unknown token type %v", t))
}
}
// Name returns the type of the Token, as a string.
func (t Token) Name() string {
return t.Type.Name()
}

13
pkg/set/set.go
View File

@@ -1,31 +1,41 @@
// 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{}
@@ -36,6 +46,8 @@ 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 {
@@ -46,6 +58,7 @@ 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]{}

25
pkg/trace/trace.go
View File

@@ -1,25 +0,0 @@
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)
}