feat: lambda

pkg/lambda/codec.go

@@ -6,12 +6,18 @@ import (
 	"git.maximhutz.com/max/lambda/pkg/codec"
 )
 
+// 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{}
 
+// 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")
 }
 
+// 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
 }

pkg/lambda/lambda.go

@@ -1,11 +1,13 @@
+// Package lambda defines the AST for the untyped lambda calculus.
 package lambda
 
-// Expression is the interface for all lambda calculus expression types.
-// It embeds the general expr.Expression interface for cross-mode compatibility.
+// 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
@@ -13,6 +15,7 @@ type Abstraction struct {
 
 func (a Abstraction) expression() {}
 
+// An Application applies an abstraction to a single argument.
 type Application struct {
 	Abstraction Expression
 	Argument    Expression
@@ -20,6 +23,7 @@ type Application struct {
 
 func (a Application) expression() {}
 
+// A Variable is a named reference to a bound or free variable.
 type Variable struct {
 	Name string
 }