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87 lines
1.8 KiB
Plaintext
87 lines
1.8 KiB
Plaintext
use Optional None Some
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optionToList : Optional a -> [a]
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optionToList = cases
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Some a -> [a]
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None -> []
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lenLit : [a] -> Nat
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lenLit = cases
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[] -> 0
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[_] -> 1
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[_, _] -> 2
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[_, _, _] -> 3
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_ -> bug "unexpected"
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lenCons : [a] -> Nat
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lenCons = cases
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[] -> 0
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_ +: t -> 1 + lenCons t
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lenSnoc : [a] -> Nat
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lenSnoc = cases
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[] -> 0
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t :+ _ -> 1 + lenSnoc t
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lenConcat1 : [a] -> Nat
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lenConcat1 = cases
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[] -> 0
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[_] ++ tail -> 1 + lenConcat1 tail
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lenConcat2 : [a] -> Nat
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lenConcat2 = cases
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[] -> 0
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prefix ++ [_] -> 1 + lenConcat2 prefix
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head : [a] -> Optional a
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head = cases
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h +: _ -> Some h
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_ -> None
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firstTwo : [a] -> Optional (a, a)
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firstTwo = cases
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x +: (y +: _) -> Some (x, y)
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_ -> None
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lastTwo : [a] -> Optional (a, a)
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lastTwo = cases
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_ :+ x :+ y -> Some (x, y)
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_ -> None
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middle : [a] -> Optional [a]
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middle = cases
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[_] ++ m ++ [_] -> Some m
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_ -> None
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middleNel : [a] -> Optional (a, [a])
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middleNel = cases
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[_] ++ (h +: t) ++ [_] -> Some (h, t)
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_ -> None
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splitAtFour : [a] -> ([a], [a])
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splitAtFour l = match l with
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[a] ++ x@(b +: (c +: y@([] :+ d))) ++ tail -> ([a, b, c, d], tail)
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_ -> (l, [])
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> (
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lenLit [1, 2, 3],
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lenCons [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
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lenSnoc [1, 2, 3, 4, 5, 6, 7, 8],
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lenConcat1 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
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lenConcat2 [1, 2, 3, 4, 5],
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optionToList (head []),
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optionToList (head [1, 2, 3]),
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optionToList (firstTwo []),
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optionToList (firstTwo [1]),
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optionToList (firstTwo [1, 2, 3]),
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optionToList (lastTwo []),
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optionToList (lastTwo [1]),
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optionToList (lastTwo [1, 2, 3]),
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optionToList (middle []),
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optionToList (middle [1, 2]),
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optionToList (middle [1, 2, 3, 4, 5, 6]),
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optionToList (middleNel []),
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optionToList (middleNel [1, 2]),
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optionToList (middleNel [1, 2, 3, 4, 5, 6]),
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splitAtFour [1, 2, 3, 4, 5, 6, 7])
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