M.V. Hutz
f3b9137d75
Closes #26 - Added -i flag to select interpreter (lambda or debruijn) - Created debruijn package with Expression interface - Variable contains index and optional label - Abstraction contains only body (no parameter) - Application structure remains similar - Implemented De Bruijn reduction without variable renaming - Shift operation handles index adjustments - Substitute replaces by index instead of name - Abstracted Engine into interface with two implementations - LambdaEngine: original named variable engine - DeBruijnEngine: new index-based engine - Added conversion functions between representations - LambdaToDeBruijn: converts named to indexed - DeBruijnToLambda: converts indexed back to named - SaccharineToDeBruijn: direct saccharine to De Bruijn - Updated main to switch engines based on -i flag - All test samples pass with both engines Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
64 lines
1.5 KiB
Go
64 lines
1.5 KiB
Go
package convert
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import (
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"fmt"
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"git.maximhutz.com/max/lambda/pkg/debruijn"
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"git.maximhutz.com/max/lambda/pkg/lambda"
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)
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// DeBruijnToLambda converts a De Bruijn expression back to named lambda calculus.
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func DeBruijnToLambda(expr debruijn.Expression) lambda.Expression {
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return deBruijnToLambda(expr, []string{})
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}
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func deBruijnToLambda(expr debruijn.Expression, context []string) lambda.Expression {
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switch e := expr.(type) {
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case *debruijn.Variable:
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if e.Index() >= 0 && e.Index() < len(context) {
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return lambda.NewVariable(context[e.Index()])
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}
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if e.Label() != "" {
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return lambda.NewVariable(e.Label())
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}
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return lambda.NewVariable(fmt.Sprintf("free_%d", e.Index()))
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case *debruijn.Abstraction:
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paramName := generateParamName(context)
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newContext := append([]string{paramName}, context...)
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body := deBruijnToLambda(e.Body(), newContext)
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return lambda.NewAbstraction(paramName, body)
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case *debruijn.Application:
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abs := deBruijnToLambda(e.Abstraction(), context)
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arg := deBruijnToLambda(e.Argument(), context)
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return lambda.NewApplication(abs, arg)
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default:
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return nil
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}
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}
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// generateParamName generates a fresh parameter name that doesn't conflict with context.
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func generateParamName(context []string) string {
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base := 'a'
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for i := 0; ; i++ {
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name := string(rune(base + rune(i%26)))
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if i >= 26 {
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name = fmt.Sprintf("%s%d", name, i/26)
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}
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conflict := false
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for _, existing := range context {
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if existing == name {
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conflict = true
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break
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}
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}
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if !conflict {
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return name
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}
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}
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}
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