35 lines
1.1 KiB
Text
35 lines
1.1 KiB
Text
--| Tag each element of the `NonEmpty` list with its index
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let NonEmpty = ./Type.dhall
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let List/map = ../List/map.dhall
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let indexed
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: ∀(a : Type) → NonEmpty a → NonEmpty { index : Natural, value : a }
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= λ(a : Type) →
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λ(xs : NonEmpty a) →
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{ head = { index = 0, value = xs.head }
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, tail =
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List/map
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{ index : Natural, value : a }
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{ index : Natural, value : a }
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( λ(ix : { index : Natural, value : a }) →
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{ index = ix.index + 1, value = ix.value }
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)
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(List/indexed a xs.tail)
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}
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let example0 =
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assert
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: indexed Bool { head = True, tail = [ False, True ] }
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≡ { head = { index = 0, value = True }
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, tail = [ { index = 1, value = False }, { index = 2, value = True } ]
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}
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let example1 =
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assert
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: indexed Bool { head = True, tail = [] : List Bool }
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≡ { head = { index = 0, value = True }
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, tail = [] : List { index : Natural, value : Bool }
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}
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in indexed
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