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https://github.com/idris-lang/Idris2.git
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63 lines
1.1 KiB
Idris
63 lines
1.1 KiB
Idris
data Tag = MkTag
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data Elem : a -> List a ->Type where
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Z : Elem a (a :: as)
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S : Elem a as -> Elem a (b :: as)
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toNat : Elem as a -> Nat
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toNat Z = 0
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toNat (S n) = 1 + toNat n
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Show (Elem as a) where
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show = show . toNat
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data Subset : List a -> List a -> Type where
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Nil : Subset [] bs
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(::) : Elem a bs -> Subset as bs -> Subset (a :: as) bs
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toList : Subset as bs -> List Nat
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toList [] = []
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toList (n :: ns) = toNat n :: toList ns
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Show (Subset as bs) where
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show = show . toList
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search : {auto prf : a} -> a
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search = prf
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test : String
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test =
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let x : Tag := MkTag
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y : Tag := MkTag
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as : List Tag
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as = [y,x]
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bs : List Tag
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bs = [x,y,y]
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prf : Subset as bs
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prf = search
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prf' : Subset as bs := search
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eq : prf === [S (S Z), Z] := Refl
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-- eq' : prf' === [S (S Z), Z] := Refl
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-- ^ does not work because prf' is opaque
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in show prf
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reverse : List a -> List a
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reverse xs =
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let revOnto : List a -> List a -> List a
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revOnto acc [] = acc
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revOnto acc (x :: xs) = revOnto (x :: acc) xs
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rev := revOnto []
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result := rev xs
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in result
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