Fixed parse problem with PARAMETERS and ARGUMENTS.

language/parser.cc

@@ -13,9 +13,9 @@ static auto g_grammar = R"(
     WHILE                 <-  'while' _ EXPRESSION BLOCK
     IF                    <-  'if' _ EXPRESSION BLOCK ('else' _ 'if' _ EXPRESSION BLOCK)* ('else' _ BLOCK)?
     FUNCTION              <-  'fn' _ PARAMETERS BLOCK
-    PARAMETERS            <-  '(' _ IDENTIFIER* ')' _ 
+    PARAMETERS            <-  '(' _ (IDENTIFIER (',' _ IDENTIFIER)*)? ')' _
     FUNCTION_CALL         <-  IDENTIFIER ARGUMENTS
-    ARGUMENTS             <-  '(' _ EXPRESSION* ')' _ 
+    ARGUMENTS             <-  '(' _ (EXPRESSION (', ' _ EXPRESSION)*)? ')' _
 
     PRIMARY               <-  CONDITION (CONDITION_OPERATOR CONDITION)?
     CONDITION             <-  TERM (TERM_OPERATOR TERM)*