Add Enum.slice_before/2 and Stream.slice_before/2

[igas]

No description provided.

[josevalim]

Thank you! Do you have a use case for this particular function or other languages that provide it?

[igas]

Sure, currently I work on slim and ast for it, and I need many other enums also, this is first one. I have structure like this:

[{1, binary1}, {2, binary2}, {1, binary3}, {2, binary4}, {3, binary5}, {4, binary6}, {2, binary7}, {1, binary8}, {2, binary9}]

and I need something like this:

[
  {binary1, [
    {binary2, []}
  ]},
  {binary3, [
    {binary4, [
      {binary5, [
        {binary6, []}
      ]}
    ]},
    {binary7, []}
  ]},
  {binary8, [{binary9, []}]}
]

With plain recursion it's tricky for me to go back for more than 1 level of nesting.

other languages that provide it?

Ruby for example http://ruby-doc.org/core-2.2.0/Enumerable.html#method-i-slice_before

[josevalim]

Thanks. I am not a fan of the name slice_before. It doesn't fit with our use of slice. The closest thing to it is chunk_by which is similar but does not seem to fit your use case. split_on would make more sense in my opinion but I am not sure too.

[igas]

Yep, I renamed it couple of times =) split also was in my list, and chunk was prototype of this function, but as I know English split is slice of 2 pieces. Also it's close to splitWhen in Haskell https://hackage.haskell.org/package/split-0.1.1/docs/Data-List-Split.html but it drops element.

[igas]

@josevalim what do you think about chunk_when?

[josevalim]

I think naming it chunk_* is going to be more confusing because it is very hard to make a distinction between it and chunk_by. :S

[lexmag]

I think split_on a good candidate to the Enum.split... family.
As a reference, today we have:

• Enum.chunk... - breaking collection into multiple chunks
• Enum.partition... - partitioning by fun
• Enum.split... - splitting collection in two pieces
• Enum.slice... - taking only a slice of collection

[igas]

@lexmag as you said, split splitting collection in two pieces, but this one more like chunk. Without limit on pieces.

[lexmag]

I see, then it definitely looks like a chunk-style behaviour.

[igas]

@josevalim do you have any ideas about name?

[josevalim]

No, sorry. :(

[josevalim]

I am closing this unfortunately due to lack of progress in naming. :( Thanks @igas!