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infinisil/choice.idr

Created April 26, 2017 15:16
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choice.idr
import Data.Vect
ChooseType : (n : Nat) -> (k : Nat) -> {auto ok : LTE k n} -> Type
ChooseType n Z {ok=LTEZero} = ()
ChooseType n@(S ns) (S Z) {ok=(LTESucc oks)} = Fin n
ChooseType n@(S ns) (S ks) {ok=(LTESucc oks)} = (Fin n, ChooseType ns ks)
data Choice : (n : Nat) -> (k : Nat) -> Type where
Choose : (n : Nat) -> (k : Nat) -> { auto ok : LTE k n } ->
ChooseType n k -> Choice n k
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