I was surprised Kotlin stdlib doesn’t have standar...

# stdlib

[Igor Kolomiets]

I was surprised Kotlin stdlib doesn’t have standard function for list comprehension to get head and tail of the list:

fun <T> List<T>.headAndTail() = Pair(first(), drop(1))

Does Kotlin offer more idiomatic approach to do this?

[Chris Lee]

that’s a specialized use case that can be readily satisfied using existing API. btw, your example isn’t head and tail (unless the list is only two items).

fun <T> List<T>.headAndTail() = Pair(first(), last())

[Igor Kolomiets]

Thank you. I still think my version is ok, because tail must be the remainder of the list.

[Chris Lee]

i see. typically `tail`refers to the last item in the list. Unclear why you’d want the first item and the remainder of the list, as that’s the original list itself.

[Rob Elliot]

In FP tail normally means everything other than head

[Rob Elliot]

If you write some Haskell you'll get very used to writing recursive functions where you do something with head then call yourself with tail.

[Chris Lee]

ah, yes, all that LISP is coming back now…

[Igor Kolomiets]

recursive definition of list as first element (a head) and the rest of it (a tail) is very common in functional programming

[Chris Lee]

understood. perhaps see if there are FP libraries to add onto Kotlin (it’s not a full FP language).

[Igor Kolomiets]

there are similar constructs (and much more) in the Arrow library, but it’s too much for my modest needs.

[ephemient]

uncons makes sense when lists are fundamentally constructed with and traversed with cons cells (as in FP languages). I don't see this being a common operation in Kotlin though.