16 lines
457 B
Text
16 lines
457 B
Text
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{-|
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Unpack an `Optional` containing a `List`, defaulting to an empty list when the
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`Optional` is `None`
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-}
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let default
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: ∀(a : Type) → Optional (List a) → List a
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= λ(a : Type) →
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λ(o : Optional (List a)) →
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merge { Some = λ(l : List a) → l, None = [] : List a } o
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let example0 = assert : default Bool (None (List Bool)) ≡ ([] : List Bool)
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let example1 = assert : default Bool (Some [ True ]) ≡ [ True ]
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in default
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