Simplified constructor for identifier expressions

ast.h

    ast_expression(int oper, ast_expression *,
 		  ast_expression *, ast_expression *);
 
+   ast_expression(const char *identifier) :
+      oper(ast_identifier)
+   {
+      subexpressions[0] = NULL;
+      subexpressions[1] = NULL;
+      subexpressions[2] = NULL;
+      primary_expression.identifier = (char *) identifier;
+   }
+
    static const char *operator_string(enum ast_operators op);
 
    virtual ir_instruction *hir(exec_list *instructions,

glsl_parser.ypp

    	}
 	| IDENTIFIER
 	{
-	   ast_expression *expr =
-	      new ast_expression(ast_identifier, NULL, NULL, NULL);
-	   expr->primary_expression.identifier = $1;
-
-	   $$ = (struct ast_node *) expr;
+	   $$ = new ast_expression($1);
    	}
 	| FIELD_SELECTION
 	{
-	   ast_expression *expr =
-	      new ast_expression(ast_identifier, NULL, NULL, NULL);
-	   expr->primary_expression.identifier = $1;
-
-	   $$ = (struct ast_node *) expr;
+	   $$ = new ast_expression($1);
    	}
 	;