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maoe/ViewPatterns.hs

Created June 21, 2010 23:12
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How to use view patterns
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ViewPatterns.hs
{-# LANGUAGE PatternGuards #-}
{-# LANGUAGE ViewPatterns #-}
module ViewPatterns where
import Data.List
data EMail = EMail User Domain deriving Show
type User = String
type Domain = String
view :: String -> Maybe EMail
view ss
| (user@(_:_), _:domain)
<- break (== '@') ss = Just (EMail user domain)
view _ = Nothing
email :: String -> Maybe EMail
email (view -> x) = x
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