Created
May 29, 2014 17:03
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| test1 :: String -> Maybe Integer | |
| test1 "a" = Just 1 | |
| test1 _ = Nothing | |
| test2 :: Integer -> Integer | |
| test2 = (1+) | |
| -- does not type check! | |
| -- Calc.hs:63:9: | |
| -- Couldn't match type `Integer' with `Maybe Integer' | |
| -- Expected type: String -> Maybe Integer | |
| -- Actual type: String -> Integer | |
| -- In the expression: test2 <$> test1 | |
| -- In an equation for `test3': test3 = test2 <$> test1 | |
| -- Calc.hs:63:19: | |
| -- Couldn't match type `Maybe Integer' with `Integer' | |
| -- Expected type: String -> Integer | |
| -- Actual type: String -> Maybe Integer | |
| -- In the second argument of `(<$>)', namely `test1' | |
| -- In the expression: test2 <$> test1 | |
| -- In an equation for `test3': test3 = test2 <$> test1 | |
| test3 :: String -> Maybe Integer | |
| test3 = test2 <$> test1 | |
| -- type checks | |
| test3' :: String -> Maybe Integer | |
| test3' str = test2 <$> (test1 str) | |
| -- also type checks | |
| test3'' :: String -> Maybe Integer | |
| test3'' = fmap test2 . test1 |
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