Bulat Ziganshin wrote:
because REAL code is somewhat larger than examples. try to rewrite the following:
directory_blocks <- (`mapM` splitBy (opt_group_dir command) files_to_archive) ( \filesInOneDirectory -> do datablocks <- (`mapM` splitToSolidBlocks filesInOneDirectory) ( \filesInOneDataBlock -> do [...]
This particular snippet contains too many undefined identifiers to be rewritten effectively, but I'm very sure that the whole program can be restructured to great effect. Maybe by designing a "binary-block"-combinator language which calculates padding bytes and length headers automatically and fiddles out scheduling for fast writing to a pipe, something like that. Eventually, a binary parser combinator library which can read single bit flags and things is a must here. It may even be possible to combine the two providing a bijection between abstract file tree, "tar"-ed blocks and compressed binary file. Separate your concerns, ban IO as much as possible and any function that takes more than 15 lines is a wart. I admit that real world applications are not a good exercise to practice functional programming, but once acquired, advanced functional tactics prove very powerful. An example might be WASH/CGI which successfully abstracts session state over HTTP, a problem where Perl-Scripts are doomed and all kind of imperative buzz like JavaBeans and so on have been invented but somewhat fail to solve it for non-trivial cases. Regards, afpelmus