feat: parse saccharine, conversion incoming

pkg/saccharine/parser.go

@@ -1,6 +1,7 @@
 package saccharine
 
 import (
+	"errors"
 	"fmt"
 
 	"git.maximhutz.com/max/lambda/pkg/iterator"
@@ -41,43 +42,44 @@ func parseToken(i *TokenIterator, expected token.Type, ignoreSoftBreaks bool) (*
 	})
 }
 
-func parseExpression(i *TokenIterator) (ast.Expression, error) {
-	return iterator.Do(i, func(i *TokenIterator) (ast.Expression, error) {
-		passSoftBreaks(i)
-		peek := i.MustGet()
-
-		switch peek.Type {
-		case token.OpenParen:
-			return parseApplication(i)
-		case token.Slash:
-			return parseAbstraction(i)
-		case token.Atom:
-			return parseAtom(i)
-		default:
-			return nil, fmt.Errorf("expected expression, got '%v' (col %d)", peek.Value, peek.Column)
-		}
-	})
+func parseString(i *TokenIterator) (string, error) {
+	if tok, err := parseToken(i, token.Atom, true); err != nil {
+		return "", trace.Wrap(err, "no variable (col %d)", i.Index())
+	} else {
+		return tok.Value, nil
+	}
 }
 
-func parseParameters(i *TokenIterator) ([]string, error) {
-	return iterator.Do(i, func(i *TokenIterator) ([]string, error) {
-		variables := []string{}
+func parseBreak(i *TokenIterator) (*token.Token, error) {
+	if tok, softErr := parseRawToken(i, token.SoftBreak); softErr == nil {
+		return tok, nil
+	} else if tok, hardErr := parseRawToken(i, token.HardBreak); hardErr == nil {
+		return tok, nil
+	} else {
+		return nil, errors.Join(softErr, hardErr)
+	}
+}
 
-		for {
-			if tok, err := parseToken(i, token.Atom, true); err != nil {
-				return variables, nil
-			} else {
-				variables = append(variables, tok.Value)
+func parseList[U any](i *TokenIterator, fn func(*TokenIterator) (U, error), minimum int) ([]U, error) {
+	results := []U{}
+
+	for {
+		if u, err := fn(i); err != nil {
+			if len(results) < minimum {
+				return nil, trace.Wrap(err, "expected at least '%v' items, got only '%v'", minimum, len(results))
 			}
+			return results, nil
+		} else {
+			results = append(results, u)
 		}
-	})
+	}
 }
 
 func parseAbstraction(i *TokenIterator) (*ast.Abstraction, error) {
 	return iterator.Do(i, func(i *TokenIterator) (*ast.Abstraction, error) {
 		if _, err := parseToken(i, token.Slash, true); err != nil {
 			return nil, trace.Wrap(err, "no function slash (col %d)", i.MustGet().Column)
-		} else if parameters, err := parseParameters(i); err != nil {
+		} else if parameters, err := parseList(i, parseString, 0); err != nil {
 			return nil, err
 		} else if _, err = parseToken(i, token.Dot, true); err != nil {
 			return nil, trace.Wrap(err, "no function dot (col %d)", i.MustGet().Column)
@@ -91,28 +93,15 @@ func parseAbstraction(i *TokenIterator) (*ast.Abstraction, error) {
 
 func parseApplication(i *TokenIterator) (*ast.Application, error) {
 	return iterator.Do(i, func(i *TokenIterator) (*ast.Application, error) {
-		expressions := []ast.Expression{}
-
 		if _, err := parseToken(i, token.OpenParen, true); err != nil {
 			return nil, trace.Wrap(err, "no openning brackets (col %d)", i.MustGet().Column)
-		}
-
-		for {
-			if exp, err := parseExpression(i); err != nil {
-				if len(expressions) == 0 {
-					return nil, trace.Wrap(err, "application has no arguments")
-				}
-				break
-			} else {
-				expressions = append(expressions, exp)
-			}
-		}
-
-		if _, err := parseToken(i, token.CloseParen, true); err != nil {
+		} else if expressions, err := parseList(i, parseExpression, 1); err != nil {
+			return nil, err
+		} else if _, err := parseToken(i, token.CloseParen, true); err != nil {
 			return nil, trace.Wrap(err, "no closing brackets (col %d)", i.MustGet().Column)
+		} else {
+			return ast.NewApplication(expressions[0], expressions[1:]), nil
 		}
-
-		return ast.NewApplication(expressions[0], expressions[1:]), nil
 	})
 }
 
@@ -124,10 +113,109 @@ func parseAtom(i *TokenIterator) (*ast.Atom, error) {
 	}
 }
 
+func parseStatements(i *TokenIterator) ([]ast.Statement, error) {
+	statements := []ast.Statement{}
+
+	//nolint:errcheck
+	parseList(i, parseBreak, 0)
+
+	for {
+		if statement, err := parseStatement(i); err != nil {
+			break
+		} else if _, err := parseList(i, parseBreak, 1); err != nil {
+			break
+		} else {
+			statements = append(statements, statement)
+		}
+	}
+
+	return statements, nil
+}
+
+func parseClause(i *TokenIterator, braces bool) (*ast.Clause, error) {
+	if braces {
+		if _, err := parseToken(i, token.OpenBrace, true); err != nil {
+			return nil, err
+		}
+	}
+
+	var stmts []ast.Statement
+	var last *ast.DeclareStatement
+	var err error
+	var ok bool
+
+	if stmts, err = parseStatements(i); err != nil {
+		return nil, err
+	} else if len(stmts) == 0 {
+		return nil, fmt.Errorf("no statements in clause")
+	} else if last, ok = stmts[len(stmts)-1].(*ast.DeclareStatement); !ok {
+		return nil, fmt.Errorf("this clause contains no final return value")
+	}
+
+	if braces {
+		if _, err := parseToken(i, token.CloseBrace, true); err != nil {
+			return nil, err
+		}
+	}
+
+	return ast.NewClause(stmts[:len(stmts)-1], last.Value), nil
+}
+
+func parseExpression(i *TokenIterator) (ast.Expression, error) {
+	return iterator.Do(i, func(i *TokenIterator) (ast.Expression, error) {
+		passSoftBreaks(i)
+
+		switch peek := i.MustGet(); peek.Type {
+		case token.OpenParen:
+			return parseApplication(i)
+		case token.Slash:
+			return parseAbstraction(i)
+		case token.Atom:
+			return parseAtom(i)
+		case token.OpenBrace:
+			return parseClause(i, true)
+		default:
+			return nil, fmt.Errorf("expected expression, got '%v' (col %d)", peek.Value, peek.Column)
+		}
+	})
+}
+
+func parseLet(i *TokenIterator) (*ast.LetStatement, error) {
+	return iterator.Do(i, func(i *TokenIterator) (*ast.LetStatement, error) {
+		if parameters, err := parseList(i, parseString, 1); err != nil {
+			return nil, err
+		} else if _, err := parseToken(i, token.Assign, true); err != nil {
+			return nil, err
+		} else if body, err := parseExpression(i); err != nil {
+			return nil, err
+		} else {
+			return ast.NewLet(parameters[0], parameters[1:], body), nil
+		}
+	})
+}
+
+func parseDeclare(i *TokenIterator) (*ast.DeclareStatement, error) {
+	if value, err := parseExpression(i); err != nil {
+		return nil, err
+	} else {
+		return ast.NewDeclare(value), nil
+	}
+}
+
+func parseStatement(i *TokenIterator) (ast.Statement, error) {
+	if let, letErr := parseLet(i); letErr == nil {
+		return let, nil
+	} else if declare, declErr := parseDeclare(i); declErr == nil {
+		return declare, nil
+	} else {
+		return nil, errors.Join(letErr, declErr)
+	}
+}
+
 func Parse(tokens []token.Token) (ast.Expression, error) {
 	i := iterator.Of(tokens)
 
-	exp, err := parseExpression(i)
+	exp, err := parseClause(i, false)
 	if err != nil {
 		return nil, err
 	}