From fea749591c94ef495117b8eb88cbce139942be5f Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sat, 10 Jan 2026 21:09:35 -0500
Subject: [PATCH] refactor: rename Application.function field to
 Application.abstraction

Changed the Application struct field from 'function' to 'abstraction' for semantic clarity and consistency with the lambda calculus terminology.

Updated all references across the codebase including the getter method, constructor parameter, and usages in substitute, rename, reduce, get_free_variables, is_free_variable, and stringify functions.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
---
 pkg/lambda/expression.go         | 12 ++++++------
 pkg/lambda/get_free_variables.go |  2 +-
 pkg/lambda/is_free_variable.go   |  2 +-
 pkg/lambda/reduce.go             |  4 ++--
 pkg/lambda/rename.go             |  6 +++---
 pkg/lambda/stringify.go          |  2 +-
 pkg/lambda/substitute.go         |  6 +++---
 7 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/pkg/lambda/expression.go b/pkg/lambda/expression.go
index affaf54..f34b3b4 100644
--- a/pkg/lambda/expression.go
+++ b/pkg/lambda/expression.go
@@ -30,12 +30,12 @@ func NewAbstraction(parameter string, body Expression) *Abstraction {
 /** ------------------------------------------------------------------------- */
 
 type Application struct {
-	function Expression
-	argument Expression
+	abstraction Expression
+	argument    Expression
 }
 
-func (a *Application) Function() Expression {
-	return a.function
+func (a *Application) Abstraction() Expression {
+	return a.abstraction
 }
 
 func (a *Application) Argument() Expression {
@@ -46,8 +46,8 @@ func (a *Application) Accept(v Visitor) {
 	v.VisitApplication(a)
 }
 
-func NewApplication(function Expression, argument Expression) *Application {
-	return &Application{function: function, argument: argument}
+func NewApplication(abstraction Expression, argument Expression) *Application {
+	return &Application{abstraction: abstraction, argument: argument}
 }
 
 /** ------------------------------------------------------------------------- */
diff --git a/pkg/lambda/get_free_variables.go b/pkg/lambda/get_free_variables.go
index 72f39ac..1615aac 100644
--- a/pkg/lambda/get_free_variables.go
+++ b/pkg/lambda/get_free_variables.go
@@ -11,7 +11,7 @@ func GetFreeVariables(e Expression) *set.Set[string] {
 		vars.Remove(e.parameter)
 		return vars
 	case *Application:
-		vars := GetFreeVariables(e.function)
+		vars := GetFreeVariables(e.abstraction)
 		vars.Merge(GetFreeVariables(e.argument))
 		return vars
 	default:
diff --git a/pkg/lambda/is_free_variable.go b/pkg/lambda/is_free_variable.go
index 2aff5d4..abc9b4b 100644
--- a/pkg/lambda/is_free_variable.go
+++ b/pkg/lambda/is_free_variable.go
@@ -7,7 +7,7 @@ func IsFreeVariable(n string, e Expression) bool {
 	case *Abstraction:
 		return e.parameter != n && IsFreeVariable(n, e.body)
 	case *Application:
-		return IsFreeVariable(n, e.function) || IsFreeVariable(n, e.argument)
+		return IsFreeVariable(n, e.abstraction) || IsFreeVariable(n, e.argument)
 	default:
 		return false
 	}
diff --git a/pkg/lambda/reduce.go b/pkg/lambda/reduce.go
index 74deba2..55d366a 100644
--- a/pkg/lambda/reduce.go
+++ b/pkg/lambda/reduce.go
@@ -12,14 +12,14 @@ func ReduceOnce(e *Expression) bool {
 		case *Abstraction:
 			stack.Push(&typed.body)
 		case *Application:
-			if fn, fnOk := typed.function.(*Abstraction); fnOk {
+			if fn, fnOk := typed.abstraction.(*Abstraction); fnOk {
 				reduced := Substitute(fn.body, fn.parameter, typed.argument)
 				*top = reduced
 				return true
 			}
 
 			stack.Push(&typed.argument)
-			stack.Push(&typed.function)
+			stack.Push(&typed.abstraction)
 		}
 	}
 
diff --git a/pkg/lambda/rename.go b/pkg/lambda/rename.go
index 7a52796..bc5625c 100644
--- a/pkg/lambda/rename.go
+++ b/pkg/lambda/rename.go
@@ -23,14 +23,14 @@ func Rename(expr Expression, target string, newName string) Expression {
 		return NewAbstraction(newParam, newBody)
 
 	case *Application:
-		newFunc := Rename(e.function, target, newName)
+		newAbs := Rename(e.abstraction, target, newName)
 		newArg := Rename(e.argument, target, newName)
 
-		if newFunc == e.function && newArg == e.argument {
+		if newAbs == e.abstraction && newArg == e.argument {
 			return e
 		}
 
-		return NewApplication(newFunc, newArg)
+		return NewApplication(newAbs, newArg)
 
 	default:
 		return expr
diff --git a/pkg/lambda/stringify.go b/pkg/lambda/stringify.go
index 0769ed6..1d838b2 100644
--- a/pkg/lambda/stringify.go
+++ b/pkg/lambda/stringify.go
@@ -19,7 +19,7 @@ func (v *stringifyVisitor) VisitAbstraction(f *Abstraction) {
 
 func (v *stringifyVisitor) VisitApplication(c *Application) {
 	v.builder.WriteRune('(')
-	c.function.Accept(v)
+	c.abstraction.Accept(v)
 	v.builder.WriteRune(' ')
 	c.argument.Accept(v)
 	v.builder.WriteRune(')')
diff --git a/pkg/lambda/substitute.go b/pkg/lambda/substitute.go
index b89f8e0..fcfb043 100644
--- a/pkg/lambda/substitute.go
+++ b/pkg/lambda/substitute.go
@@ -31,14 +31,14 @@ func Substitute(expr Expression, target string, replacement Expression) Expressi
 		return NewAbstraction(param, newBody)
 
 	case *Application:
-		newFunc := Substitute(e.function, target, replacement)
+		newAbs := Substitute(e.abstraction, target, replacement)
 		newArg := Substitute(e.argument, target, replacement)
 
-		if newFunc == e.function && newArg == e.argument {
+		if newAbs == e.abstraction && newArg == e.argument {
 			return e
 		}
 
-		return NewApplication(newFunc, newArg)
+		return NewApplication(newAbs, newArg)
 
 	default:
 		return expr