CartesianProduct.hs

{-| Module  : FiniteCategories
Description : Simple functions to compute cartesian products of finite lists.
Copyright   : Guillaume Sabbagh 2021
License     : GPL-3
Maintainer  : guillaumesabbagh@protonmail.com
Stability   : experimental
Portability : portable

Simple functions to compute cartesian products of finite lists.
-}

module Utils.CartesianProduct
(
    cartesianProduct,
    cartesianPower,
    (|*|),
    (|^|)
)
where
    import Data.List (replicate)

    -- | Returns the cartesian product of the finite lists.
    --
    -- cartesianProduct [A,B,C,...] = A x B x C x ...
    cartesianProduct :: [[a]] -> [[a]]
    cartesianProduct [] = [[]]
    cartesianProduct (x:xs) = concat ((\l -> [e:l | e <- x]) <$> (cartesianProduct xs))
    
    -- | Returns the cartesian product of two lists
    (|*|) :: [a] -> [a] -> [[a]]
    x |*| y = cartesianProduct [x,y]

    -- | Returns the cartesian product of a list by itself /k/ times.
    cartesianPower :: [a] -> Int -> [[a]]
    cartesianPower l k = cartesianProduct $ replicate k l
    
    -- | Infix alias for `cartesianPower`
    (|^|) = cartesianPower