Re: [Haskell-cafe] Heavy lift-ing

I think the point that was being made is that:

liftM2 (flip f) /= flip (liftM2 f)

This is because the former (well: liftM2 (flip f) a b) effectively does:

do {x <- a; y <- b; return (f y x)}

Whereas the latter (flip (liftM2 f) a b) effectively does:

do {y <- b; x <- a; return (f y x)}

That is, the order of the arguments to liftM2 matters because they are executed in that order. So lifting the flipped function has a different effect to flipping the lifted function.

Thanks,

Neil.

Thanks, I can see how that could lead to confusion.