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(.module:
[lux (#- type)
["." meta]
[abstract
[predicate (#+ Predicate)]]
[macro
[syntax (#+ syntax:)]]
[type (#+ :by_example)
abstract]])
(abstract: #export (Refined t r)
{#value t
#predicate (Predicate t)}
{#.doc "A refined type 'r' of base type 't' using a predicate."}
(type: #export (Refiner t r)
(-> t (Maybe (Refined t r))))
(def: #export (refinement predicate)
(All [t]
(Ex [r]
(-> (Predicate t) (Refiner t r))))
(function (_ un_refined)
(if (predicate un_refined)
(#.Some (:abstraction {#value un_refined
#predicate predicate}))
#.None)))
(template [<name> <output> <slot>]
[(def: #export (<name> refined)
(All [t r] (-> (Refined t r) <output>))
(|> refined :representation (get@ <slot>)))]
[un_refine t #value]
[predicate (Predicate t) #predicate]
)
(def: #export (lift transform)
(All [t r]
(-> (-> t t)
(-> (Refined t r) (Maybe (Refined t r)))))
(function (_ refined)
(let [[value predicate] (:representation refined)
value' (transform value)]
(if (predicate value')
(#.Some (:abstraction {#value value'
#predicate predicate}))
#.None))))
)
(def: #export (filter refiner values)
(All [t r] (-> (Refiner t r) (List t) (List (Refined t r))))
(case values
#.Nil
#.Nil
(#.Cons head tail)
(case (refiner head)
(#.Some refined)
(#.Cons refined (filter refiner tail))
#.None
(filter refiner tail))))
(def: #export (partition refiner values)
(All [t r] (-> (Refiner t r) (List t) [(List (Refined t r)) (List t)]))
(case values
#.Nil
[#.Nil #.Nil]
(#.Cons head tail)
(let [[yes no] (partition refiner tail)]
(case (refiner head)
(#.Some refined)
[(#.Cons refined yes)
no]
#.None
[yes
(#.Cons head no)]))))
(syntax: #export (type refiner)
(meta.with_gensyms [g!t g!r]
(wrap (list (` ((~! :by_example) [(~ g!t) (~ g!r)]
{(..Refiner (~ g!t) (~ g!r))
(~ refiner)}
(..Refined (~ g!t) (~ g!r))))))))
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