feat: parser

pkg/parser/parser.go

@@ -0,0 +1,72 @@
+package parser
+
+import (
+	"fmt"
+
+	"git.maximhutz.com/max/lambda/pkg/iterator"
+	"git.maximhutz.com/max/lambda/pkg/lambda"
+	"git.maximhutz.com/max/lambda/pkg/tokenizer"
+)
+
+func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression, error) {
+	token, err := i.Next()
+	if err != nil {
+		return nil, fmt.Errorf("Could not get next token: %w", err)
+	}
+
+	switch token.Type {
+	case tokenizer.TokenAtom:
+		return lambda.Atom{Value: token.Value}, nil
+	case tokenizer.TokenDot:
+		return nil, fmt.Errorf("Token '.' found without a corresponding slash (column %d).", token.Index)
+	case tokenizer.TokenSlash:
+		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.TokenAtom {
+			return nil, fmt.Errorf("Expected function parameter, 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)
+		}
+
+		body, body_err := ParseExpression(i)
+		if body_err != nil {
+			return nil, fmt.Errorf("Could not parse function body: %w", body_err)
+		}
+
+		return lambda.Function{Parameter: atom.Value, Body: body}, 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)
+		}
+
+		arg, arg_err := ParseExpression(i)
+		if arg_err != nil {
+			return nil, fmt.Errorf("Could not parse call argument: %w", arg_err)
+		}
+
+		close, close_err := i.Next()
+		if close_err != nil {
+			return nil, fmt.Errorf("Could not parse call terminating parenthesis: %w", close_err)
+		} else if close.Type != tokenizer.TokenCloseParen {
+			return nil, fmt.Errorf("Expected call terminating parenthesis, got '%v' (column %v).", close.Value, close.Index)
+		}
+
+		return lambda.Call{Function: fn, Argument: arg}, nil
+	case tokenizer.TokenCloseParen:
+		return nil, fmt.Errorf("Token ')' found without a corresponding openning parenthesis (column %d).", token.Index)
+	default:
+		return nil, fmt.Errorf("Unknown token '%v' (column %d).", token.Value, token.Index)
+	}
+}
+
+func GetTree(tokens []tokenizer.Token) (lambda.Expression, error) {
+	i := iterator.New(tokens)
+	return ParseExpression(&i)
+}