Well I'm trying to combine two monads here, Maybe and either the Fay or the
IO monad. In the example code I just put return but otherwise in my real
code "operation" has side-effects and needs the Fay monad in the case of
the Fay program.
I understand how to use lift if "operation" is pure, without using monads,
but I have this trouble when it operates in another monad. I thought I
understood it, but looking at the difference in behaviour in the examples I
posted, maybe I don't.
Emmanuel
On Sat, Sep 7, 2013 at 9:11 AM, Daniel Trstenjak wrote: Hello Emmanuel, And I tried to apply it to the haskell fay compiler, but failed: http://stackoverflow.com/questions/18667530/dont-understand-this-liftm2-beha... Not sure whether it's a fay bug or something about the fay monad or liftM2
which i don't understand. The point of lifting is, that you lift an operation into an other
"context", so
that the operation itself hasn't to operate in the same "context". I can't see how even your GHC version of 'operation' should work,
because in both cases it should be something like: liftM2 (++) getValue1 getValue2 or in applicative style (++) <$> getValue1 <*> getValue2 Greetings,
Daniel _______________________________________________
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