I suspected that it was in Read monad, but I don't see where is it this
"Read" monad here :) Francesco, thank you very much!!
Absolutely clear :)
В Thu, 13 Jul 2017 11:06:13 +0200
Francesco Ariis
On Thu, Jul 13, 2017 at 11:29:56AM +0300, Baa wrote:
main :: IO () main = f0 >>= do f1 f2 >> print "end"
and I get output:
"f2!" 10 "end"
Hello Paul, your `main` desugars to
main = f0 >>= (f1 >> f2) >> print "end"
Now, the quizzical part is
λ> :t (f1 >> f2) (f1 >> f2) :: Int -> IO Int
Why does this even type checks? Because:
λ> :i (->) [..] instance Monad ((->) r) -- Defined in ‘GHC.Base’ [..]
((->) r) is an instance of Monad! The instance is:
instance Monad ((->) r) where f >>= k = \r -> k (f r) r
you already know that `m >> k` is defined as `m >>= \_ -> k`, so
f >> k = \r -> (\_ -> k) (f r) r = \r -> k r
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