allow for loop to use postfix and compound infix operators for assign…

…ments

examples/scratch.ghost

@@ -1,17 +1,6 @@
-data = {
-  name: 'Test',
-  handler: function(n) {
-    print('n * n')
+x = 0
+list = [0, 1, 2, 3]
 
-    return n * n
-  }
-}
-
-print(data.name)
-print(data.handler(6))
-
-function test1() {
-  print('test1')
-}
-
-test1()
+for (i = 0; i < list.length(); i++) {
+  print(i)
+}

parser/for.go

@@ -40,7 +40,7 @@ func (parser *Parser) forExpression() ast.ExpressionNode {
 	parser.readToken()
 	parser.readToken()
 
-	expression.Increment = parser.assign()
+	expression.Increment = parser.forIncrement()
 
 	if expression.Increment == nil {
 		return nil
@@ -107,3 +107,39 @@ func (parser *Parser) forInExpression(parent *ast.For) ast.ExpressionNode {
 
 	return expression
 }
+
+// forIncrement parses the increment expression of a for loop.
+// It can be an assignment (x = x + 1), a postfix expression (x++), or an infix expression (x += 1).
+func (parser *Parser) forIncrement() ast.ExpressionNode {
+	if parser.currentTokenIs(token.RIGHTPAREN) {
+		return nil
+	}
+
+	if parser.currentTokenIs(token.SEMICOLON) {
+		parser.readToken()
+		return nil
+	}
+
+	if parser.currentTokenIs(token.IDENTIFIER) && parser.nextTokenIs(token.EQUAL) {
+		return parser.assign()
+	}
+
+	if parser.currentTokenIs(token.IDENTIFIER) && (parser.nextTokenIs(token.PLUSEQUAL) ||
+		parser.nextTokenIs(token.MINUSEQUAL) ||
+		parser.nextTokenIs(token.SLASHEQUAL) ||
+		parser.nextTokenIs(token.STAREQUAL)) {
+		identifier := parser.identifierLiteral()
+
+		parser.readToken()
+
+		return parser.compoundExpression(identifier)
+	}
+
+	if parser.currentTokenIs(token.IDENTIFIER) && (parser.nextTokenIs(token.PLUSPLUS) || parser.nextTokenIs(token.MINUSMINUS)) {
+		parser.readToken()
+
+		return parser.postfixExpression()
+	}
+
+	return nil
+}