Particularly the last two paragraphs. > Am 22.11.2016 um 17:32 schrieb Janis Voigtländer > <janis.voigtlaen...@gmail.com>: > > Have you seen what is written at the following location? > > https://github.com/elm-lang/core/blob/master/CONTRIBUTING.md#adding-new-functions > > >> Am 22.11.2016 um 17:21 schrieb Martin Cerny <cern...@gmail.com>: >> >> Hi all, >> I am currently about 3 side projects (small games) deep in Elm and the >> experience has been overally very good. I however encountered a few simple >> things I missed in the core libraries, so I would like to ask, if there is a >> reason to not have them there. If not, I'll be happy to file a pull request >> with them :-) >> >> So here they are, in order of decreasing importance (IMHO) >> >> 1) List.get : Int -> List a -> Maybe a >> Just a way to get the nth element of a linked list in O(n) time. (the >> signature mimics that of Array.get). I know this exists in >> http://package.elm-lang.org/packages/circuithub/elm-list-extra/3.10.0/List-Extra >> but seems important enough to have it in the core. >> >> 2) Random.constant : a -> Generator a >> A generator that is not really a generator, but returns a fixed value. This >> is useful for composing generators with Random.map and Random.andThen or for >> the base case of recursive generators. An example use case is if I want to >> pick a value that is zero 50% percent of the time and 1-5 otherwise >> (happened in my game a few times) >> This one is already present in >> http://package.elm-lang.org/packages/mgold/elm-random-pcg/latest/Random-Pcg >> which, according to https://github.com/elm-lang/core/issues/724 should >> replace the core Random in the future, but why not add it now :-) >> >> generateValue : Bool -> Generator Float >> generateValue isZero = >> if isZero then Random.constant 0 else Random.float 1 5 >> >> >> Random.bool |> Random.andThen generateValue >> >> it also lets you write things like (which is probably not a very common use >> case, but came in handy for me): >> >> listOfGeneratorsToGeneratorOfList : List (Random.Generator a) -> >> Random.Generator (List a) >> listOfGeneratorsToGeneratorOfList listOfGenerators = >> case listOfGenerators of >> head :: tail -> >> Random.andThen >> (listOfGeneratorsToGeneratorOfList tail) >> (\list -> Random.map (\x -> x :: list) head) >> >> [] -> >> Random.constant [] >> >> currently, you can declare constant generator like this, but it seems stupid >> and wasteful: >> >> constant : a -> Random.Generator a >> constant value = >> Random.map (\_ -> value) Random.bool >> >> 3) Random.permutation : List a -> Generator (List a) >> This would simply pick a permutation of the original list at random. Might >> make sense to write this in javascript via converstion to array, as the O(n) >> algorithm (Knuth shuffle) for this does not seem to translate well into pure >> functional world... I currently do not see a purely functional >> implementation that is not O(n^2), but I'll be happy to be proven wrong :-) >> >> I understand that it is important to keep the core library slim (especially >> until dead code elimination is brought to Elm), so which of those you think >> should make the cut? >> >> Looking forward to your ideas >> Martin Černý >> -- >> You received this message because you are subscribed to the Google Groups >> "Elm Discuss" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to elm-discuss+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout.
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