Make curry idempotent such that curry(curry(f)) -> curry(f)

[eriknw]

This may be done by having a Curry class and a curry function.

[mrocklin]

Yeah, I was thinking about how best to do that. I prefer class Curry/def curry solution to Curry.__new__. Another option is to unpack the func, args, and kwargs from the argument curried function and then repack them into self.

[eriknw]

Yeah, I considered those options too. I don't want to use __new__.

Consider the following:

@curry
def f(x, y):
    return x + y

g = curry(f)

g is f

Do we want g is f to evaluate as True or False? This is the main difference between the other two options.

[mrocklin]

I don't have a strong opinion one way or the other. Both seem like reasonable options. What is your opinion?

[eriknw]

I'm leaning towards unpacking func, args, and kwargs, but my paranoia has not yet run its course.

[mrocklin]

Making a separate curry function seems totally reasonable. It's what we do for compose.

[eriknw]

Yeah, both seem reasonable, and both behaviors are of course possible with curry as a function. def curry/class Curry does seem to be the most clean.

If f is a curry instance and g = f(some_args) is still a curry or partial instance, then I would expect h = curry(g) to make h an instance of curry regardless of whether g is a curry or partial instance, which implies (g is h) is False.

How much of an advantage is there for a curried object to return a partial if only one more argument is needed? Having multiple return types muddies the waters a bit.

[mrocklin]

The performance increase for using partial was substantial. This is particularly important for cases like

map(get(0), lots_of_data)

[eriknw]

Figured as much, because you wouldn't have bothered with the hassle otherwise.

Okay, so lets make curry a function and Curry a class. The curry function will always return a new functools.partial (if appropriate) or Curry instance. If the callable passed to curry is an instance of functools.partial or Curry, then the func, args, and keywords attributes will be used to instantiate a new object (along with any additional *args and **kwargs passed to curry of course).

[eriknw]

I have created a branch to address this issue (https://github.com/eriknw/toolz/tree/curry_class). It is not yet ready, but feedback and PRs are most welcome.

The main change is that a curried instance uses functools.partial, but never returns a functoolz.partial instance. This is because curry and partial behave differently. For example, doing @memoize(cache={1: 2}) doesn't work if memoize is partial.

I have not performed any benchmarks, and the pickle protocol still needs implemented.

[eriknw]

Closing. Idempotency implemented in #170