In the specific case of parsing --version strings, I'm not sure regexes
are any easier. Using words and then selecting the Nth word seems to do
pretty well.
for comparison, see the examples below:-) There's no reason
this can't be massaged further, but it already allows for IO if
necessary (I like that it is compact and self-documenting -the
comments have become part of the patterns, but if you don't
want to match against the precise message format, you can use
more of [^[:space:]]* - pity that \S* isn't posix..).
Claus
import Text.Regex
import System.Process(runInteractiveProcess)
import System.IO(hGetContents)
test = mapM_ ((print =<<) . getVersion) programs
getVersion (prg,flag,io,extract) = do
(i,o,e,p) <- runInteractiveProcess prg [flag] Nothing Nothing
version <- hGetContents ([o,e]!!(io-1)) >>= extract
return (prg,version)
defaultMatch :: String -> String -> IO String
defaultMatch pattern = return . maybe "" head . (matchRegex (mkRegex pattern))
programs = [ghc,ghcPkg,happy,alex,haddock]
ghc = ("ghc","--numeric-version",1,
defaultMatch "([^[:space:]]*)")
ghcPkg = ("ghc-pkg","--version",1,
defaultMatch "GHC package manager version ([^[:space:]]*)")
happy = ("happy","--version",1,
defaultMatch "Happy Version ([^[:space:]]*)")
alex = ("alex","--version",1,
defaultMatch "Alex version ([.0-9]*)")
haddock = ("haddock","--version",1,
defaultMatch "Haddock version ([.0-9]*)")
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