mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-15 14:23:32 +03:00
93022af74e
Another one from the "stop trying to be clever" files :). Instead of a continuation for fallthrough in the evaluator, be explicit about whether there's a result, no match, or evaluation is stuck. Fixes #70
28 lines
923 B
Idris
28 lines
923 B
Idris
import Data.Vect
|
|
|
|
%default total
|
|
|
|
infix 3 .<=.
|
|
(.<=.) : Int -> Int -> Bool
|
|
(.<=.) p q = case (p, q) of
|
|
(0, _) => True
|
|
_ => False
|
|
|
|
countGreater : (thr : Int) -> (ctx : Vect n Int) -> Nat
|
|
countGreater thr [] = Z
|
|
countGreater thr (x :: xs) with (x .<=. thr)
|
|
countGreater thr (x :: xs) | True = countGreater thr xs
|
|
countGreater thr (x :: xs) | False = S $ countGreater thr xs
|
|
|
|
-- map a variable from the old context to the erased context
|
|
-- where we erase all bindings less than or equal to the threshold
|
|
eraseVar : (thr : Int) -> (ctx : Vect n Int) -> Fin n -> Maybe (Fin (countGreater thr ctx))
|
|
eraseVar thr (x :: xs) j with (x .<=. thr)
|
|
eraseVar thr (x :: xs) FZ | True = Nothing
|
|
eraseVar thr (x :: xs) FZ | False = Just FZ
|
|
eraseVar thr (x :: xs) (FS i) | True = FS <$> eraseVar thr xs i
|
|
eraseVar thr (x :: xs) (FS i) | False = FS <$> eraseVar thr xs i
|
|
|
|
boom : Maybe (Fin 1)
|
|
boom = eraseVar 0 [0, 1] (FS FZ)
|