feat: Add tap function

[vlad-iakovlev]

Replace this quote with a description of your changes

See #149, #114

Make sure that you:

• [ ] Typedoc added for new methods and updated for changed
• [ ] Tests added for new methods and updated for changed
• [ ] New methods added to src/index.ts
• [ ] New methods added to mapping.md

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[TkDodo]

any chance we can add the lazy version as described here?

• https://github.com/remeda/remeda/pull/114#issuecomment-754524515

[vlad-iakovlev]

@TkDodo not changed yet. See if there any way to implement this on current version of pipe

As I read discussion, @lstkz suggested here to run fn callback on every lazy call. That already could be done with R.map(R.tap(fn)), no changes required. It that way is ok, let's left as-is.

For me more interesting to make tap that will run tap callback in pipe with array but only with those element that will go through the pipe (like in this test). That's what I'm trying to implement now

[vlad-iakovlev]

@TkDodo I totally forgot how should R.pipe(['a', 'b', 'c'], R.tap(console.log)) print result?

1. 3 calls with 'a', 'b', 'c'
2. 1 call with 'a,b,c' or something like that?

[paour]

I hope you can continue with this PR, tap is a very useful quick debug tool.

[eranhirsch]

@vlad-yakovlev, it's been almost a year since this was opened, where do we stand regarding this, do you want to see it shipped? I'm closing the PR for now for housekeeping, but feel free to open it again and I'll see what I can do to help.

[cjquines]

hey, i do want to see this merged, i think the current implementation works fine as-is?

R.pipe(['a', 'b', 'c'], R.tap(console.log)) has console.log called once

R.pipe(['a', 'b', 'c'], R.map(R.tap(console.log))) has console.log called thrice

in particular i dont think R.tap should be lazy, as it does not take an array as input, it takes in any T and returns T?

with respect to

For me more interesting to make tap that will run tap callback in pipe with array but only with those element that will go through the pipe (like in this test). That's what I'm trying to implement now

i think this is fine if not implemented? that would mean having different behavior if the input type is an array or not

as another example, consider R.identity, which in theory could be lazy, but is not:

R.pipe(['a', 'b', 'c'], R.identity, R.take(1)) means R.identity still gets called with ['a', 'b', 'c']

(maybe it'd be nice if it was lazy, but i would consider this a change that will change other functions as well, and it would change behavior)

[TkDodo]

in particular i dont think R.tap should be lazy

why not? As shown in this example, we'd only expect 3 logs, not 5

R.pipe(
  [1, 2, 3, 4, 5],
  R.tap(console.log),
  R.take(3)
);

I don't mind if we don't have that in the first version, but since it works for other functions, it should work for tap, too, don't you think?

[cjquines]

i did say that i think this example would have one log:

R.pipe(
  [1, 2, 3, 4, 5],
  R.tap(console.log),
  R.take(3)
);

should log [1, 2, 3, 4, 5], while

R.pipe(
  [1, 2, 3, 4, 5],
  R.map(R.tap(console.log)),
  R.take(3)
);

should log 1, then 2, then 3. it follows from map being lazy, not tap.

the type of tap should be T => T, not T[] => T.