Proposal: add ifM and whenM to Control.Monad

[Mario Pastorelli]

On 04/21/2014 06:03 PM, Casey McCann wrote:
> On Mon, Apr 21, 2014 at 11:33 AM, Mario Pastorelli
> <pastorelli.mario at gmail.com> wrote:
>> On 04/21/2014 04:22 PM, Casey McCann wrote:
>>> Has anyone noticed yet that replicateM is already breaking the
>>> ostensibly established naming scheme, and should properly be named
>>> mreplicate?
>>
>> Sadly, replicateM breaks the naming scheme in a different way than ifM. The
>> first doesn't justify the existence of the latter.
> But it does somewhat deflate the notion that the fooM convention is
> consistently used, especially since replicateM and replicateM_ are
> probably more frequently used than many of the properly-named
> functions.
>
>>> But perhaps we should in fact rename replicateM. Certainly
>>> "mreplicate" would fit in better with other monadic variants of list
>>> functions, like "mconcat"! Consistency is important, after all.
>>>
>>> Also, mfix should probably be fixM, for what that's worth.
>>
>> Don't you think that for compatibility reason this can be very problematic?
>> How many people already used replicateM (and replicateM_) in their code? How
>> many times?
> Ah, so you're arguing that API consistency is sometimes outweighed by
> other concerns? I suppose I can't disagree with that. ;]
>
> Naming things is a matter of human language, and as a rule of thumb if
> everyone consistently breaks a linguistic "rule" in exactly the same
> way, it was the wrong rule. Figuring out what the actual rule being
> followed is and making it explicit is far more useful than trying to
> force a rule that runs counter to intuition.
>
> These functions have been reinvented many, many times under the names
> ifM &c., and between that and the strong association between the m
> prefix and MonadPlus/Monoid (as demonstrated by the fact you
> apparently didn't notice I compared "mreplicate" to "mconcat" above) I
> would argue that mif &c. are actually more misleading in this case,
> for the clear and simple reason that they're not the names most people
> would expect.
>
> Unless we plan to be absolutely and completely consistent, including
> renaming replicateM and mfix, we should use the widely established
> names in this case.
>
> - C.

Yes, I think you are right. +1 for ifM, whenM and unlessM.