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disolovyov/read_fallback.hs

Created August 5, 2012 09:15
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Read from strings with a fallback on error
Raw
read_fallback.hs
{-# LANGUAGE ScopedTypeVariables #-}
fromStr :: Read a => a -> String -> a
fromStr fallback s =
let parsed = reads s :: Read a => [(a, String)]
in case parsed of
[(result, _)] -> result
_ -> fallback
p :: Show a => a -> IO ()
p = putStrLn . show
main = do
p $ fromStr 0 "100"
p $ fromStr 0.0 "100"
p $ fromStr 0 "10x"
p $ fromStr 0 "xxx"
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