for package:utility-ht

Split the list before each occurence of a leading character. Keep these characters. There is always a list for the part before the first leading character. It may be empty. See package non-empty for more precise result type.

>>> segmentBefore isUpper "AbcdXyz"
["","Abcd","Xyz"]

>>> segmentBefore isUpper "kAbcdXYZ"
["k","Abcd","X","Y","Z"]

forAllPredicates $ \p xs -> concat (segmentBefore p xs) == xs

forAllPredicates $ \p xs -> length (filter p xs) == length (tail (segmentBefore p xs))

forAllPredicates $ \p -> all (p . head) . tail . segmentBefore p

forAllPredicates $ \p -> all (all (not . p) . tail) . tail . segmentBefore p

forAllPredicates $ \p x -> flip seq True . (!!100) . concat . segmentBefore p . cycle . (x:)

>>> segmentBeforeJust (\c -> toMaybe (isLetter c) (toUpper c)) "123a5345b---"
("123",[('A',"5345"),('B',"---")])

Deprecated: use segmentBeforeJust instead

>>> segmentBeforeRight [Left 'a', Right LT, Right GT, Left 'b']
("a",[(LT,""),(GT,"b")])

forAllMaybeFn $ \f xs -> segmentBeforeJust f xs == segmentBeforeRight (map (\x -> maybe (Left x) Right (f x)) xs)