feat: lambda expressions are mutable now

pkg/convert/saccharine_to_lambda.go

@@ -10,7 +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 {
@@ -27,7 +27,7 @@ func encodeAbstraction(n *saccharine.Abstraction) lambda.Expression {
 	}
 
 	for i := len(parameters) - 1; i >= 0; i-- {
-		result = lambda.NewAbstraction(parameters[i], result)
+		result = lambda.Abstraction{Parameter: parameters[i], Body: result}
 	}
 
 	return result
@@ -43,7 +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
@@ -58,19 +58,19 @@ func reduceLet(s *saccharine.LetStatement, e lambda.Expression) lambda.Expressio
 		value = encodeAbstraction(&saccharine.Abstraction{Parameters: s.Parameters, Body: s.Body})
 	}
 
-	return lambda.NewApplication(
+	return lambda.Application{
-		lambda.NewAbstraction(s.Name, e),
+		Abstraction: lambda.Abstraction{Parameter: s.Name, Body: e},
-		value,
+		Argument:    value,
-	)
+	}
 }
 
 func reduceDeclare(s *saccharine.DeclareStatement, e lambda.Expression) lambda.Expression {
 	freshVar := lambda.GenerateFreshName(e.GetFree())
 
-	return lambda.NewApplication(
+	return lambda.Application{
-		lambda.NewAbstraction(freshVar, e),
+		Abstraction: lambda.Abstraction{Parameter: freshVar, Body: e},
-		encodeExpression(s.Value),
+		Argument:    encodeExpression(s.Value),
-	)
+	}
 }
 
 func reduceStatement(s saccharine.Statement, e lambda.Expression) lambda.Expression {
@@ -112,15 +112,15 @@ func encodeExpression(s saccharine.Expression) lambda.Expression {
 func decodeExression(l lambda.Expression) saccharine.Expression {
 	switch l := l.(type) {
 	case lambda.Variable:
-		return &saccharine.Atom{Name: l.Name()}
+		return &saccharine.Atom{Name: l.Name}
 	case lambda.Abstraction:
 		return &saccharine.Abstraction{
-			Parameters: []string{l.Parameter()},
+			Parameters: []string{l.Parameter},
-			Body:       decodeExression(l.Body())}
+			Body:       decodeExression(l.Body)}
 	case lambda.Application:
 		return &saccharine.Application{
-			Abstraction: decodeExression(l.Abstraction()),
+			Abstraction: decodeExression(l.Abstraction),
-			Arguments:   []saccharine.Expression{decodeExression(l.Argument())}}
+			Arguments:   []saccharine.Expression{decodeExression(l.Argument)}}
 	default:
 		panic(fmt.Errorf("unknown expression type: %T", l))
 	}

pkg/engine/normalorder/reduce_once.go

@@ -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 {
+		if fn, fnOk := e.Abstraction.(lambda.Abstraction); fnOk {
-			return fn.Body().Substitute(fn.Parameter(), e.Argument()), true
+			return fn.Body.Substitute(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

pkg/lambda/get_free_variables.go

@@ -3,17 +3,17 @@ package lambda
 import "git.maximhutz.com/max/lambda/pkg/set"
 
 func (e Variable) GetFree() set.Set[string] {
-	return set.New(e.Name())
+	return set.New(e.Name)
 }
 
 func (e Abstraction) GetFree() set.Set[string] {
-	vars := e.Body().GetFree()
+	vars := e.Body.GetFree()
-	vars.Remove(e.Parameter())
+	vars.Remove(e.Parameter)
 	return vars
 }
 
 func (e Application) GetFree() set.Set[string] {
-	vars := e.Abstraction().GetFree()
+	vars := e.Abstraction.GetFree()
-	vars.Merge(e.Argument().GetFree())
+	vars.Merge(e.Argument.GetFree())
 	return vars
 }

pkg/lambda/is_free_variable.go

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

pkg/lambda/lambda.go

@@ -32,69 +32,25 @@ type Expression interface {
 /** ------------------------------------------------------------------------- */
 
 type Abstraction struct {
-	parameter string
+	Parameter string
-	body      Expression
+	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
+	Abstraction Expression
-	argument    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
+	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}
-}

pkg/lambda/rename.go

@@ -2,27 +2,27 @@ 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 {
+	if e.Name == target {
-		return NewVariable(newName)
+		return Variable{Name: newName}
 	}
 
 	return e
 }
 
 func (e Abstraction) Rename(target string, newName string) Expression {
-	newParam := e.Parameter()
+	newParam := e.Parameter
-	if e.Parameter() == target {
+	if e.Parameter == target {
 		newParam = newName
 	}
 
-	newBody := e.Body().Rename(target, newName)
+	newBody := e.Body.Rename(target, newName)
 
-	return NewAbstraction(newParam, newBody)
+	return Abstraction{Parameter: newParam, Body: newBody}
 }
 
 func (e Application) Rename(target string, newName string) Expression {
-	newAbs := e.Abstraction().Rename(target, newName)
+	newAbs := e.Abstraction.Rename(target, newName)
-	newArg := e.Argument().Rename(target, newName)
+	newArg := e.Argument.Rename(target, newName)
 
-	return NewApplication(newAbs, newArg)
+	return Application{Abstraction: newAbs, Argument: newArg}
 }

pkg/lambda/stringify.go

@@ -0,0 +1,13 @@
+package lambda
+
+func (a Abstraction) String() string {
+	return "\\" + a.Parameter + "." + a.Body.String()
+}
+
+func (a Application) String() string {
+	return "(" + a.Abstraction.String() + " " + a.Argument.String() + ")"
+}
+
+func (v Variable) String() string {
+	return v.Name
+}

pkg/lambda/substitute.go

@@ -1,7 +1,7 @@
 package lambda
 
 func (e Variable) Substitute(target string, replacement Expression) Expression {
-	if e.Name() == target {
+	if e.Name == target {
 		return replacement
 	}
 
@@ -9,12 +9,12 @@ func (e Variable) Substitute(target string, replacement Expression) Expression {
 }
 
 func (e Abstraction) Substitute(target string, replacement Expression) Expression {
-	if e.Parameter() == target {
+	if e.Parameter == target {
 		return e
 	}
 
-	body := e.Body()
+	body := e.Body
-	param := e.Parameter()
+	param := e.Parameter
 	if replacement.IsFree(param) {
 		freeVars := replacement.GetFree()
 		freeVars.Merge(body.GetFree())
@@ -24,12 +24,12 @@ func (e Abstraction) Substitute(target string, replacement Expression) Expressio
 	}
 
 	newBody := body.Substitute(target, replacement)
-	return NewAbstraction(param, newBody)
+	return Abstraction{Parameter: param, Body: newBody}
 }
 
 func (e Application) Substitute(target string, replacement Expression) Expression {
-	abs := e.Abstraction().Substitute(target, replacement)
+	abs := e.Abstraction.Substitute(target, replacement)
-	arg := e.Argument().Substitute(target, replacement)
+	arg := e.Argument.Substitute(target, replacement)
 
-	return NewApplication(abs, arg)
+	return Application{Abstraction: abs, Argument: arg}
 }