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11 lines
319 B
Plaintext
11 lines
319 B
Plaintext
data Maybe : Type -> Type where
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Nothing : (A : Type) -> Maybe A
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Just : (A : Type) -> A -> Maybe A
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fromMaybe : (A : Type) -> A -> Maybe A -> A
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fromMaybe _ x Nothing = x
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fromMaybe _ _ (Just x) = x
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maybe : (A : Type) -> (B : Type) -> B -> (A -> B) -> Maybe A -> A
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maybe _ _ x _ Nothing = x
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maybe _ _ _ f (Just x) = f x |