better one line binary readers in haskell, thanks to commenters and redditors.

update to my previous post on binary readers.

from roconnor:

readBin s = x
where
[(x,"")] = Numeric.readInt 2 (`elem` "01") Char.digitToInt s -- probably the best way of doing it; reinventing what's available in the standard libraries isn't a good thing.

and two from pjdelport:

readBin = foldM (\a d -> (a*2 +) <$> elemIndex d "01") 0 -- as elemIndex evaluates to a Maybe, (<$>) or fmap is necessary to lift the arithmetic section into the Maybe. bonus points for using Maybe instead of error. readBin = (foldl' ((+) . (*2)) 0 <$>) . mapM (`elemIndex` "01") — this version separates “parsing” and summing the values of each bit. otherwise same benefits as the previous versions.

that’s it for now.