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ttuegel/gist:9a3be681985fc5837a38

Created January 24, 2015 00:09
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Function application versus evaluation
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gistfile1.txt
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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