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28 lines
923 B
Idris
28 lines
923 B
Idris
import Data.Vect
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%default total
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infix 3 .<=.
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(.<=.) : Int -> Int -> Bool
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(.<=.) p q = case (p, q) of
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(0, _) => True
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_ => False
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countGreater : (thr : Int) -> (ctx : Vect n Int) -> Nat
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countGreater thr [] = Z
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countGreater thr (x :: xs) with (x .<=. thr)
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countGreater thr (x :: xs) | True = countGreater thr xs
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countGreater thr (x :: xs) | False = S $ countGreater thr xs
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-- map a variable from the old context to the erased context
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-- where we erase all bindings less than or equal to the threshold
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eraseVar : (thr : Int) -> (ctx : Vect n Int) -> Fin n -> Maybe (Fin (countGreater thr ctx))
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eraseVar thr (x :: xs) j with (x .<=. thr)
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eraseVar thr (x :: xs) FZ | True = Nothing
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eraseVar thr (x :: xs) FZ | False = Just FZ
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eraseVar thr (x :: xs) (FS i) | True = FS <$> eraseVar thr xs i
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eraseVar thr (x :: xs) (FS i) | False = FS <$> eraseVar thr xs i
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boom : Maybe (Fin 1)
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boom = eraseVar 0 [0, 1] (FS FZ)
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