{-# LANGUAGE NoImplicitPrelude, UnicodeSyntax #-}

module Data.List.Unicode
    ( (⧺)
    , (∈), (∋), (∉), (∌)
    , (∪), (∖), (∆), (∩)
    , (‼)
    , 𝜀
    ) where

-------------------------------------------------------------------------------
-- Imports
-------------------------------------------------------------------------------

-- from base:
import Prelude       ( Int )
import Data.Bool     ( Bool )
import Data.Eq       ( Eq )
import Data.Function ( flip )
import Data.List     ( (++), elem, notElem, union, (\\), intersect, (!!) )


-------------------------------------------------------------------------------
-- Fixities
-------------------------------------------------------------------------------

infix  4 ∈
infix  4 ∋
infix  4 ∉
infix  4 ∌
infixr 5 ⧺
infixl 6 ∪
infixr 6 ∩
infixl 9 ∖
infixl 9 ∆
infixl 9 ‼


-------------------------------------------------------------------------------
-- Symbols
-------------------------------------------------------------------------------

{-|
(⧺) = ('++')

U+29FA, DOUBLE PLUS
-}
(⧺) ∷ [α] → [α] → [α]
(⧺) = (++)
{-# INLINE (⧺) #-}

{-|
(∈) = 'elem'

U+2208, ELEMENT OF
-}
(∈) ∷ Eq α ⇒ α → [α] → Bool
(∈) = elem
{-# INLINE (∈) #-}

{-|
(∋) = 'flip' (∈)

U+220B, CONTAINS AS MEMBER
-}
(∋) ∷ Eq α ⇒ [α] → α → Bool
(∋) = flip (∈)
{-# INLINE (∋) #-}

{-|
(∉) = 'notElem'

U+2209, NOT AN ELEMENT OF
-}
(∉) ∷ Eq α ⇒ α → [α] → Bool
(∉) = notElem
{-# INLINE (∉) #-}

{-|
(∌) = 'flip' (∉)

U+220C, DOES NOT CONTAIN AS MEMBER
-}
(∌) ∷ Eq α ⇒ [α] → α → Bool
(∌) = flip (∉)
{-# INLINE (∌) #-}

{-|
(∪) = 'union'

U+222A, UNION
-}
(∪) ∷ Eq α ⇒ [α] → [α] → [α]
(∪) = union
{-# INLINE (∪) #-}

{-|
(∖) = ('\\')

U+2216, SET MINUS
-}
(∖) ∷ Eq α ⇒ [α] → [α] → [α]
(∖) = (\\)
{-# INLINE (∖) #-}

{-|
Symmetric difference

a ∆ b = (a ∖ b) ∪ (b ∖ a)

U+2206, INCREMENT
-}
(∆) ∷ Eq α ⇒ [α] → [α] → [α]
a ∆ b = (a ∖ b) ∪ (b ∖ a)
{-# INLINE (∆) #-}

{-|
(∩) = 'intersect'

U+2229, INTERSECTION
-}
(∩) ∷ Eq α ⇒ [α] → [α] → [α]
(∩) = intersect
{-# INLINE (∩) #-}

{-|
(‼) = ('!!')

U+203C, DOUBLE EXCLAMATION MARK
-}
(‼) ∷ [α] → Int → α
(‼) = (!!)
{-# INLINE (‼) #-}

{-|
Epsilon, the empty word (or list)

(ε) = []

(U+3B5, GREEK SMALL LETTER EPSILON)
-}
𝜀 ∷ [a]
𝜀 = []