Add fmap built-in

[evhub]

fmap would look like:

def fmap(func, obj) =
    obj |> map$(func) |*> obj.__class__

[Sitwon]

Is the intention here a variation on map that returns an iterable of the same kind?
Eg, list -> list, tuple -> tuple, str -> str?

[evhub]

@Sitwon Yep, that's exactly it! There was a discussion on Gitter that this stems from about adding more FP-style tools to Coconut. The rationale is that if you added a function like the above, it would make it a lot easier to do this:

>>> data Nothing()
>>> data Just(n)
>>> Just(3) |> map$(-> _*2) |*> Just
Just(n=6)
>>> Nothing() |> map$(-> _*2) |*> Nothing
Nothing()

[evhub]

An interesting question--should there also be a parallel_fmap and a concurrent_fmap in addition to just fmap? I can't see an obvious use case, but it's possible one exists.

[hasufell]

This doesn't work on lists as expected though:

[1,2,3] |> fmap$(_ -> _ + 1)

yields

TypeError: list() takes at most 1 argument (3 given)

[evhub]

@hasufell Agreed. I just finished a much more complicated version that should do the trick, however. I've put it up on coconut-develop, so if you want to test it out just pip install coconut-develop and you should be able to play around with the new fmap function there.

[evhub]

@hasufell @Sitwon This is now ready to be released on the v1.2.3 milestone. You can check it out now on coconut-develop with pip install coconut-develop (like I said above).

[hasufell]

On develop branch I get the following error for python-2.7:

Compiling /var/tmp/paludis/build/dev-lang-coconut-scm/image//usr/x86_64-pc-linux-gnu/lib/python2.7/site-packages/coconut/command/mypy.py ...
SyntaxError: 'return' with argument inside generator (mypy.py, line 44)

[evhub]

@hasufell I have no idea how you managed to trigger that error--why are you trying to compile mypy.py?

[hasufell]

why are you trying to compile

Because that's what my package manager does when I install coconut.

[evhub]

@hasufell Huh. What package manager are you using? Are you not installing Coconut through pip?

Regardless, I changed the code around a bit and that file should compile fine on 2.7 now, though it still should never be run except on Python 3. Try it now!

[hasufell]

Huh. What package manager are you using? Are you not installing Coconut through pip?

No, I'm using paludis under exherbo. I've packaged coconut manually.

Try it now!

Yes, works now!