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26 lines
763 B
Idris
26 lines
763 B
Idris
module Data.So
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||| Ensure that some run-time Boolean test has been performed.
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||| This lifts a Boolean predicate to the type level. See the function `choose`
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||| if you need to perform a Boolean test and convince the type checker of this
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||| fact.
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||| If you find yourself using `So` for something other than primitive types,
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||| it may be appropriate to define a type of evidence for the property that you
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||| care about instead.
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public export
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data So : Bool -> Type where
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Oh : So True
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export
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implementation Uninhabited (So False) where
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uninhabited Oh impossible
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||| Perform a case analysis on a Boolean, providing clients with a `So` proof
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export
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choose : (b : Bool) -> Either (So b) (So (not b))
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choose True = Left Oh
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choose False = Right Oh
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