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Couple of useful Maybe functions (#44)

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Patrick Stevens
2019-09-15 15:08:51 +01:00
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parent 8c51b9b3d1
commit d4ebcc04ce
1 changed files with 6 additions and 0 deletions
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6
Maybe.agda
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@@ -31,3 +31,9 @@ module Maybe where
defaultValue : {a : _} → {A : Set a} → (default : A) → Maybe A → A defaultValue : {a : _} → {A : Set a} → (default : A) → Maybe A → A
defaultValue default no = default defaultValue default no = default
defaultValue default (yes x) = x defaultValue default (yes x) = x
noNotYes : {a : _} {A : Set a} {b : A} → (no ≡ yes b) → False
noNotYes ()
mapMaybePreservesNo : {a b : _} {A : Set a} {B : Set b} (f : A → B) (x : Maybe A) → mapMaybe f x ≡ no → x ≡ no
mapMaybePreservesNo f no pr = refl