On Mon, Apr 21, 2014 at 12:01 PM, Dan Doel
Yes, I think the stated naming conventions are somewhat off on what is really in the module.
mfoo is generalizing foo to monads-with-extra-structure, in Control.Monad at least.
But fooM is generally about functions that 'sequence' multiple actions. For instance:
mapM f = sequence . map f
This also explains replicateM, as:
replicateM n = sequence . replicate n
And liftM through liftM5 are similar.
ifM, whenM, unlessM, etc. do not involve monads with extra structure, but they are about sequencing extra monadic stuff, which seems to be what the M suffix is actually about. So they seem like the better names.
I would actually say that the M suffix is primarily used to indicate that sequential control flow is involved. In Control.Monad that amounts to very simple loop-like constructs, but in other code the fooM convention seems to appear most often on functions that want to do something to a data structure while binding only those monadic values corresponding to constructors that would be created/evaluated in the pure version. Thus why the M prefix is so commonly used when reinventing simple conditional statements. Not sure how that would apply to liftM & co., though. - C.