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|
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Data.String
-- {{{ Num literals
newtype N = N Int deriving (Show,Eq)
instance Num N where
fromInteger 0 = error "0"
fromInteger 1 = N 0
fromInteger _ = N 1
f x = case x of
1 -> False
0 -> True
g x = case x of
1 -> False
_ -> case x of
0 -> True
_ -> error "No match"
testNum = do
print $ g (N 0)
print $ f (N 0)
-- }}}
-- {{{ IsString literals
newtype S = S String deriving Eq
instance IsString S where
fromString [] = error "[]"
fromString (_:_) = S "."
fs x = case x of
"." -> False
"" -> True
gs x = case x of
"." -> False
_ -> case x of
"" -> True
_ -> error "No match"
testIsString = do
print $ gs (S ".")
print $ fs (S ".")
-- }}}
main = do { testNum; testIsString }
|
