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Add cons, snoc, unsnoc #125

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Jun 13, 2017
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Add cons, snoc, unsnoc #125

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14 changes: 14 additions & 0 deletions src/Data/List/NonEmpty.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,11 +5,14 @@ module Data.List.NonEmpty
, fromList
, toList
, singleton
, cons
, snoc
, head
, last
, tail
, init
, uncons
, unsnoc
, length
, concatMap
, appendFoldable
Expand Down Expand Up @@ -47,6 +50,12 @@ toList (NonEmptyList (x :| xs)) = x : xs
singleton :: forall a. a -> NonEmptyList a
singleton = NonEmptyList <<< NE.singleton

cons :: forall a. a -> NonEmptyList a -> NonEmptyList a
cons y (NonEmptyList (x :| xs)) = NonEmptyList (y :| x : xs)

snoc :: forall a. NonEmptyList a -> a -> NonEmptyList a
snoc (NonEmptyList (x :| xs)) y = NonEmptyList (x :| L.snoc xs y)

head :: forall a. NonEmptyList a -> a
head (NonEmptyList (x :| _)) = x

Expand All @@ -62,6 +71,11 @@ init (NonEmptyList (x :| xs)) = maybe L.Nil (x : _) (L.init xs)
uncons :: forall a. NonEmptyList a -> { head :: a, tail :: L.List a }
uncons (NonEmptyList (x :| xs)) = { head: x, tail: xs }

unsnoc :: forall a. NonEmptyList a -> { init :: L.List a, last :: a }
unsnoc (NonEmptyList (x :| xs)) = case L.unsnoc xs of
Nothing -> { init: L.Nil, last: x }
Just un -> { init: x : un.init, last: un.last }

length :: forall a. NonEmptyList a -> Int
length (NonEmptyList (x :| xs)) = 1 + L.length xs

Expand Down