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(.module:
{#.doc "Functionality for working with variants (particularly 2-variants)."}
lux)
(do-template [<name> <type> <index>]
[(def: #export (<name> value)
(All [a b] (-> <type> (| a b)))
(<index> value))]
[left a +0]
[right b +1])
(def: #export (either fl fr)
(All [a b c]
(-> (-> a c) (-> b c)
(-> (| a b) c)))
(function (_ input)
(case input
(+0 l) (fl l)
(+1 r) (fr r))))
(def: #export (each fl fr)
(All [l l' r r']
(-> (-> l l') (-> r r')
(-> (| l r) (| l' r'))))
(function (_ input)
(case input
(+0 l) (+0 (fl l))
(+1 r) (+1 (fr r)))))
(do-template [<name> <side> <tag>]
[(def: #export (<name> es)
(All [a b] (-> (List (| a b)) (List <side>)))
(case es
#.Nil #.Nil
(#.Cons (<tag> x) es') (#.Cons [x (<name> es')])
(#.Cons _ es') (<name> es')))]
[lefts a +0]
[rights b +1]
)
(def: #export (partition xs)
(All [a b] (-> (List (| a b)) [(List a) (List b)]))
(case xs
#.Nil
[#.Nil #.Nil]
(#.Cons x xs')
(let [[lefts rights] (partition xs')]
(case x
(+0 x') [(#.Cons x' lefts) rights]
(+1 x') [lefts (#.Cons x' rights)]))))
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