Re: [Haskell-cafe] parsing exercise

I don't think you can do this "simply" as you think you would always have to build a parse tree. If the input is valid Haskell you could follow Chung-chieh Shan's suggestion, otherwise you could parse to a "skeleton syntax tree" - look for work by Jonathan Bacharach on Dylan macros and "Java Syntax Extension". In practice, if you follow the skeleton syntax tree style you might find "not caring" about the details of syntax is almost as much work as caring about them. I've tried a couple of times to make a skeleton parser that does paren nesting and little else, but always given up and just used a proper parser as the skeleton parser never seemed robust.