[erlang-questions] Proposal: add lists:intersperse/2 and lists:intercalate/2

Jesper Louis Andersen jesper.louis.andersen@REDACTED
Wed Mar 2 15:47:41 CET 2016

Hi Erlangers,

I'd really like to add two functions to the lists module from Haskell:

intersperse(List, Seperator) produces a list where each element is
separated by separator, i.e.

X = [1,2,3]
[1, x, 2, x, 3] = lists:intersperse(X, x),

and it's cousin, intercalate(ListOfLists, Separator) is
append(intersperse(ListOfLists, Seperator)), i.e,

Y = ["a", "b", "c"]
"a, b, c" = lists:intercalate(Y, ", "),

The implementations are straightforward and easy to write tests for, even
property based tests if needed.

The rationale for this proposal is that I find myself implementing this
function again and again in every project I write, and it is highly
generic. It belongs in a typical list module. OCaml libraries add it.
Haskell's Data.List has it. I believe Erlang, being a practical language,
should have it as well.


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