Mapping a list to a shuffled version of itself

Shuffle.elm

module Main exposing (..)

import Array
import Tuple
import Dict exposing (Dict, get)
import Random exposing (Generator, map)


-- RANDOM


zip : List a -> List b -> List ( a, b )
zip =
    List.map2 (,)


constant : a -> Generator a
constant a =
    Random.map (\_ -> a) Random.bool


shuffle : List comparable -> Generator (List comparable)
shuffle list =
    Random.list (List.length list) (Random.int 1 3)
        |> Random.map (zip list)
        |> Random.map (List.sortBy Tuple.second)
        |> Random.map (List.map Tuple.first)


shuffledMappings : List comparable -> Generator (Dict comparable comparable)
shuffledMappings list =
    shuffle list
        |> Random.map (zip list)
        |> Random.map (Dict.fromList)


draw : List comparable -> Generator (Maybe (Dict comparable comparable))
draw list =
    if List.length list < 2 then
        constant Nothing
    else
        shuffledMappings list
            |> Random.map Just