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Variant with error text.

Variant of unzip.

let r = ([Just 1,Nothing,Just 3],[Just 'a',Nothing,Just 'c'])
in maybe_unzip [Just (1,'a'),Nothing,Just (3,'c')] == r

Replace Nothing elements with last Just value. This does not alter the length of the list.

maybe_latch 1 [Nothing,Just 2,Nothing,Just 4] == [1,2,2,4]

Variant requiring initial value is not Nothing.

maybe_latch1 [Just 1,Nothing,Nothing,Just 4] == [1,1,1,4]

map of fmap.

maybe_map negate [Nothing,Just 2] == [Nothing,Just (-2)]

If either is Nothing then False, else eq of values.

Join two values, either of which may be missing.

maybe_join' of id

Apply predicate inside Maybe.

maybe_predicate even (Just 3) == Nothing

map of maybe_predicate.

let r = [Nothing,Nothing,Nothing,Just 4]
in maybe_filter even [Just 1,Nothing,Nothing,Just 4] == r

Variant of catMaybes. If all elements of the list are Just a, then gives Just [a] else gives Nothing.

all_just (map Just [1..3]) == Just [1..3]
all_just [Just 1,Nothing,Just 3] == Nothing