Sanctuary: Type representation for generator functions

[arsaniwilliam]

executing this in the repl

S.prop('a', {a : function*(){return 12}} )

results in

TypeError: Type-variable constraint violation

prop :: Accessible a => String -> a -> b
                                       ^
                                       1

1)  function* (){return 12} ::

Since there is no type of which all the above values are members, the type-variable constraint has been violated.

It used to work before, now it's breaking.
Is there a type representation for generator functions? (is this even the issue? i'm not completely sure)
I'm currently using the latest version of ES6

[davidchambers]

The problem is that function*() { return 12; } is not a member of any of the types in S.env.

One solution is to update the definition of $.AnyFunction. The current definition is essentially:

x => Object.prototype.toString.call(x) === '[object Function]'

Generator functions do not satisfy this predicate. We could use this predicate instead:

x => typeof x === 'function'

If you're interested, @arsaniwilliam, you could submit a pull request for sanctuary-def. Specifically, you would need to update AnyFunction.

[arsaniwilliam]

@davidchambers Thanks for the explanation.
I will submit a pull request soon.

[arsaniwilliam]

merge request was created
1 problem though.. I added a line in the test to check that generator functions pass as well, but the es3 linter fails to parse the * .. not sure how to get around that - short of not writing a test.

[gabejohnson]

@arsaniwilliam see this SO question

[davidchambers]

Thank you for the pull request, Arsani! :)

[arsaniwilliam]

My pleasure! This is my first public contribution on github and i'm glad it's to Sanctuary :)

[arsaniwilliam]

So here's a thought.. at some point should we make the distinction between "normal" functions and Generator function types?
I think that was the case before 0.12.x

[davidchambers]

We could define $.AnyGeneratorFunction, but for now I'm happy to let users define this type in their own code. I'm not sure yet whether such a type is useful.

[davidchambers]

$ npm install [email protected]
$ node --print 'require("sanctuary").prop("a", {a: function*() { return 12; }})'
[Function: a]