fix: unbound substitutions, explanation tag

.gitignore

@@ -25,3 +25,4 @@ go.work.sum
 # env file
 .env
 
+*.log

cmd/lambda/lambda.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"time"
 
 	"git.maximhutz.com/max/lambda/internal/cli"
 	"git.maximhutz.com/max/lambda/pkg/lambda"
@@ -35,9 +36,21 @@ func main() {
 	cli.HandleError(err)
 	logger.Info("Parsed syntax tree.", "tree", lambda.Stringify(expression))
 
-	for lambda.ReduceOnce(&expression) {
-		logger.Info("Reduction.", "tree", lambda.Stringify(expression))
-	}
+	start := time.Now()
 
+	if options.Explanation {
 		fmt.Println(lambda.Stringify(expression))
 	}
+
+	for lambda.ReduceOnce(&expression) {
+		logger.Info("Reduction.", "tree", lambda.Stringify(expression))
+		if options.Explanation {
+			fmt.Println("    =", lambda.Stringify(expression))
+		}
+	}
+
+	elapsed := time.Since(start).Milliseconds()
+
+	fmt.Println(lambda.Stringify(expression))
+	fmt.Fprintln(os.Stderr, "Time Spent:", elapsed, "ms")
+}

internal/cli/arguments.go

@@ -8,11 +8,13 @@ import (
 type CLIOptions struct {
 	Input       string
 	Verbose     bool
+	Explanation bool
 }
 
 func ParseOptions(args []string) (*CLIOptions, error) {
 	// Parse flags and arguments.
 	verbose := flag.Bool("v", false, "Verbosity. If set, the program will print logs.")
+	explanation := flag.Bool("x", false, "Explanation. Whether or not to show all reduction steps.")
 	flag.Parse()
 
 	if flag.NArg() == 0 {
@@ -24,5 +26,6 @@ func ParseOptions(args []string) (*CLIOptions, error) {
 	return &CLIOptions{
 		Input:       flag.Arg(0),
 		Verbose:     *verbose,
+		Explanation: *explanation,
 	}, nil
 }

pkg/lambda/substitute.go

@@ -20,7 +20,7 @@ func Substitute(e *Expression, target string, replacement Expression) {
 		used := GetFreeVariables(typed.Body)
 		used.Union(replacement_free_vars)
 		fresh_var := GenerateFreshName(used)
-		Rename(typed.Body, typed.Parameter, fresh_var)
+		Rename(typed, typed.Parameter, fresh_var)
 		Substitute(&typed.Body, target, replacement)
 	case *Application:
 		Substitute(&typed.Abstraction, target, replacement)

pkg/parser/parser.go

@@ -20,18 +20,23 @@ func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression,
 	case tokenizer.TokenDot:
 		return nil, fmt.Errorf("Token '.' found without a corresponding slash (column %d).", token.Index)
 	case tokenizer.TokenSlash:
+		atoms := []string{}
+
+		for {
 			atom, atom_err := i.Next()
 			if atom_err != nil {
-			return nil, fmt.Errorf("Could not find parameter of function: %w", atom_err)
-		} else if atom.Type != tokenizer.TokenVariable {
-			return nil, fmt.Errorf("Expected function parameter, got '%v' (column %d).", atom.Value, atom.Index)
+				return nil, fmt.Errorf("Could not find parameter or terminator of function: %w", atom_err)
+			} else if atom.Type == tokenizer.TokenVariable {
+				atoms = append(atoms, atom.Value)
+			} else if atom.Type == tokenizer.TokenDot {
+				break
+			} else {
+				return nil, fmt.Errorf("Expected function parameter or terminator, got '%v' (column %d).", atom.Value, atom.Index)
+			}
 		}
 
-		dot, dot_err := i.Next()
-		if dot_err != nil {
-			return nil, fmt.Errorf("Could not find function parameter terminator: %w", dot_err)
-		} else if dot.Type != tokenizer.TokenDot {
-			return nil, fmt.Errorf("Expected function parameter terminator, got '%v' (column %v).", dot.Value, dot.Index)
+		if len(atoms) == 0 {
+			return nil, fmt.Errorf("Every function must have atleast one parameter (column %d)", token.Index)
 		}
 
 		body, body_err := ParseExpression(i)
@@ -39,18 +44,34 @@ func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression,
 			return nil, fmt.Errorf("Could not parse function body: %w", body_err)
 		}
 
-		return lambda.NewAbstraction(atom.Value, body), nil
+		// Construction.
+		result := body
+		for i := len(atoms) - 1; i >= 0; i-- {
+			result = lambda.NewAbstraction(atoms[i], result)
+		}
+
+		return result, nil
 	case tokenizer.TokenOpenParen:
 		fn, fn_err := ParseExpression(i)
 		if fn_err != nil {
 			return nil, fmt.Errorf("Could not parse call function: %w", fn_err)
 		}
 
+		args := []lambda.Expression{}
+
+		for {
+			if next, next_err := i.Peek(); next_err == nil && next.Type == tokenizer.TokenCloseParen {
+				break
+			}
+
 			arg, arg_err := ParseExpression(i)
 			if arg_err != nil {
 				return nil, fmt.Errorf("Could not parse call argument: %w", arg_err)
 			}
 
+			args = append(args, arg)
+		}
+
 		close, close_err := i.Next()
 		if close_err != nil {
 			return nil, fmt.Errorf("Could not parse call terminating parenthesis: %w", close_err)
@@ -58,7 +79,13 @@ func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression,
 			return nil, fmt.Errorf("Expected call terminating parenthesis, got '%v' (column %v).", close.Value, close.Index)
 		}
 
-		return lambda.NewApplication(fn, arg), nil
+		// Construction.
+		result := fn
+		for _, arg := range args {
+			result = lambda.NewApplication(result, arg)
+		}
+
+		return result, nil
 	case tokenizer.TokenCloseParen:
 		return nil, fmt.Errorf("Token ')' found without a corresponding openning parenthesis (column %d).", token.Index)
 	default:

samples/simple.txt

@@ -1 +1,16 @@
-(\add.(add (add (add \f.\x.x))) \n.\f.\x.(f ((n f) x)))
+(\0.
+  (\inc.
+    (\add.
+      (\mult.
+        (\exp.
+          (exp (inc (inc (inc (inc (inc 0))))) (inc (inc (inc (inc (inc 0))))))
+          \n m.(m n)
+        )
+        \m n f.(m (n f))
+      )
+      \n m.(m inc n)
+    )
+    \n f x.(f (n f x))
+  )
+  \f x.x
+)