Re: [Haskell-cafe] Stacking monads

Andrew Coppin wrote:

...

"ap" generalizes the liftM* functions, so

liftM2 f a b = return f `ap` a `ap` b liftM3 f a b c = return f `ap` a `ap` b `ap` c

and so forth.

Now that at least makes sense. (It's non-obvious that you can use it for this. If it weren't for curried functions, this wouldn't work at all...)

Note that the documentation for ap states:

In many situations, the liftM operations can be replaced by uses of ap, which promotes function application.

return f `ap` x1 `ap` ... `ap` xn

is equivalent to

liftMn f x1 x2 ... xn

Tillmann