Curry trouble (example for R.is)

[noobiek]

Hi,

I understand this has to do with curry, but I constantly have trouble with R.is because of this, so...
The troube comes when I do something like this
if (R.is(Array, someVar)) { ... }
Now, if someVar is undefined then R.is will return function, so the check will pass.
This may happen in a bigger scope, when my function accepts an object A, and one of its fields B should be an array:

function myFunc(A) {
...
  if (R.is(Array, A.B)) { ... }
...
}

So, if B was not defined, the IF block will proceed as if B were an array.
I can add an additional check
if (A.B && R.is(Array, A.B)) { ... }
But that just doesn't feel and look right. Right?

[Dejan Toteff]

Please try it now with the latest version.

[noobiek]

Hi,
Thanks! Checked out the code, looks OK.
I think that will work nicely.

[noobiek]

Hi,
Would be nice to have this change for the rest of curried functions.
R.map, for examples, suffers from this situation. One could argue that it is up to user to check if supplied value is defined or undefined, but at least lodash/underscore (which I used before) don't care, they return an empty array in such cases.

[Dejan Toteff]

Ok, so what is your suggestion. map to return [] when undefined is provided instead of array, or I am missing something?

[noobiek]

Yes, that would be consistent with how underscore/lodash work (I guess a lot of people are used to how map() and filter() work there) - return []. And this proved to be convinient, as in some cases you are not sure if some object property will be present (say, Person.PhoneNumbers can be set or not), but you don't have to check, since map() and filter() will return [] and the rest of code won't break. Without this convinience you would still do something like R.map(func, Person.PhoneNumbers||[]) each time.

But I guess in the end it must be your decision as lib architect/maintainer. At least R.map(i=>i, undefined) and R.filter(i=>i, undefined) should not return curried functions. This is definitely unexpected since I provided 2 arguments not 1 in each case.

[Dejan Toteff]

After such thorough explanation, I have no other option but to integrate your suggestion in the next version of Rambda.

[noobiek]

...so that everyone can blame me if this proves to be completely wrong. 🤣
Sure, why not!

[noobiek]

Same with R.merge().
If I run R.merge({...}, undefined) I get curried function returned. Meanwhile Object.assign({a:1}, undefined) works without problems. So I have to R.merge({...}, undefined||{})....

[noobiek]

Hi,
Any news/plans for this?

[Dejan Toteff]

It should be ready by the end of the week.

[Dejan Toteff]

All should be fixed with the new version. Reopen, if that is not the case.

[noobiek]

Hi,

I don't think that your approach covers all cases (at least, in case of "null" it will throw an exception). Please, see how it's done in Lodash. Your code looks somewhat alike, but not quite.

function arrayMap(array, iteratee) {
    var index = -1,
        length = array == null ? 0 : array.length,
        result = Array(length);

    while (++index < length) {
      result[index] = iteratee(array[index], index, array);
    }
    return result;
}

Do you think it is better to check if arr is an array by "arr.length === undefined"?
Why not use R.is(Obect, arr) and R.is(Array, arr), for example?

[Dejan Toteff]

I will consider your latest suggestion in the next release.

[Dejan Toteff]

I decided null to keep throwing in filter/map as otherwise Rambda will differ too much from Ramda. Imagine the surprise of fellow developers when they expect filter(fn, null) to throw and it doesn't.
undefined is different case and you make a good argument to have a saveguard for it.

I replaced arr.length === undefined with !Array.isArray(arr) if just for readability sake(thanks for pointing that out).

So I will close the issue, as version 1.2.2 addresses alread the following:

expect(R.merge(null, undefined)).toEqual({})
expect(R.map(R.add(1), undefined)).toEqual([])
expect(R.filter(Boolean, undefined)).toEqual([])