fix if/then errors

parser/parser.go

@@ -157,7 +157,18 @@ func (p *Parser) parseIfStatement() *IfStatement {
 		return nil
 	}
 
-	p.nextToken() // move past condition
+	// Optional 'then' keyword
+	if p.peekTokenIs(THEN) {
+		p.nextToken()
+	}
+
+	p.nextToken() // move past condition (and optional 'then')
+
+	// Check if we immediately hit END (missing body)
+	if p.curTokenIs(END) {
+		p.addError("expected 'end' to close if statement")
+		return nil
+	}
 
 	// Parse if body
 	stmt.Body = p.parseBlockStatements(ELSEIF, ELSE, END)
@@ -174,7 +185,12 @@ func (p *Parser) parseIfStatement() *IfStatement {
 			return nil
 		}
 
-		p.nextToken() // move past condition
+		// Optional 'then' keyword
+		if p.peekTokenIs(THEN) {
+			p.nextToken()
+		}
+
+		p.nextToken() // move past condition (and optional 'then')
 
 		elseif.Body = p.parseBlockStatements(ELSEIF, ELSE, END)
 		stmt.ElseIfs = append(stmt.ElseIfs, elseif)
@@ -563,6 +579,8 @@ func tokenTypeString(t TokenType) string {
 		return "var"
 	case IF:
 		return "if"
+	case THEN:
+		return "then"
 	case ELSEIF:
 		return "elseif"
 	case ELSE:

parser/token.go

@@ -29,6 +29,7 @@ const (
 	// Keywords
 	VAR
 	IF
+	THEN
 	ELSEIF
 	ELSE
 	END
@@ -74,6 +75,7 @@ func lookupIdent(ident string) TokenType {
 		"false":  FALSE,
 		"nil":    NIL,
 		"if":     IF,
+		"then":   THEN,
 		"elseif": ELSEIF,
 		"else":   ELSE,
 		"end":    END,