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(;module: {#;doc "Functionality for working with variants (particularly 2-variants)."}
lux)
## [Values]
(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 f g s)
(All [a b c] (-> (-> a c) (-> b c) (| a b) c))
(case s
(+0 x) (f x)
(+1 x) (g x)))
(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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