On 26.04 11:29, Anton Kulchitsky wrote:
I just started to study Haskell and it is my almost first big experience with functional languages (except Emacs Lisp and Python). I enjoyed all small exercises and started a bigger business writing a general utility. However, I have a problem from the beginning. The utility get some file and convert it to another format. It is a kind of small compiler. It also accepts many parameters and behaves depending on them. The problem is how to do this neat! How should I write my program to accept and neatly work with options????
One solution is to have a datatype for configuration:
data Config = Config { mode :: Mode, infile :: Maybe FilePath, outfile :: Maybe FilePath } nullConfig = Config Normal "-" "-" data Mode = Normal | Version | Help
and handle options as functions from Config to Config:
Option ['i'] ["input"] (ReqArg (\x c -> c { infile = Just x }) "file") "input file name"
and then handle the parsed options like:
case conf of Config Normal (Just i) (Just o) -> ... Config Normal _ _ -> both input and output must be specified Config Help _ _ -> help message
- Einar Karttunen