Created
January 24, 2015 00:09
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Function application versus evaluation
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| ghci> import Control.Monad (liftM) | |
| ghci> :t liftM | |
| liftM :: Monad m => (a1 -> r) -> m a1 -> m r | |
| ghci> import Debug.Trace (trace) | |
| ghci> liftM (\x -> trace "function applied" (x + 3)) [1 :: Int, 2, 3] | |
| [function applied | |
| 4,function applied | |
| 5,function applied | |
| 6] | |
| ghci> liftM (trace "function evaluated" (+ 3)) [1 :: Int, 2, 3] | |
| [function evaluated | |
| 4,5,6] |
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