feat: only compute all free variables during a-conversion

.gitignore

@@ -26,3 +26,5 @@ go.work.sum
 .env
 
 *.log
+
+profile/

Makefile

@@ -13,5 +13,13 @@ thunk: it
 saccharine: it
 	@ ./lambda.exe - < ./samples/saccharine.txt
 
+prof:
+	@ go tool pprof -top profile/cpu.prof
+
+graph:
+	@ go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof
+	@ go tool pprof -svg profile/cpu.prof > profile/cpu.svg
+	@ open profile/cpu.svg
+
 saccharineX: it
 	@ ./lambda.exe -x - < ./samples/saccharine.txt > saccharine.out

cmd/lambda/lambda.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"runtime/pprof"
 	"time"
 
 	"git.maximhutz.com/max/lambda/internal/cli"
@@ -14,6 +15,14 @@ import (
 
 // Run main application.
 func main() {
+	f, err := os.Create("profile/cpu.prof")
+	cli.HandleError(err)
+	defer f.Close()
+
+	err = pprof.StartCPUProfile(f)
+	cli.HandleError(err)
+	defer pprof.StopCPUProfile()
+
 	options, err := config.FromArgs()
 	cli.HandleError(err)
 

pkg/lambda/is_free_variable.go

@@ -0,0 +1,14 @@
+package lambda
+
+func IsFreeVariable(n string, e Expression) bool {
+	switch e := e.(type) {
+	case *Variable:
+		return e.Value == n
+	case *Abstraction:
+		return e.Parameter != n && IsFreeVariable(n, e.Body)
+	case *Application:
+		return IsFreeVariable(n, e.Abstraction) || IsFreeVariable(n, e.Argument)
+	default:
+		return false
+	}
+}

pkg/lambda/substitute.go

@@ -11,12 +11,12 @@ func Substitute(e *Expression, target string, replacement Expression) {
 			return
 		}
 
-		replacementFreeVars := GetFreeVariables(replacement)
-		if !replacementFreeVars.Has(typed.Parameter) {
+		if !IsFreeVariable(typed.Parameter, replacement) {
 			Substitute(&typed.Body, target, replacement)
 			return
 		}
 
+		replacementFreeVars := GetFreeVariables(replacement)
 		used := GetFreeVariables(typed.Body)
 		used.Merge(replacementFreeVars)
 		freshVar := GenerateFreshName(used)