haskell - What are Alternative's "some" and "many" useful for? -


alternative, extension of applicative, declares empty, <|> , these 2 functions:

one or more:

some :: f -> f [a]

zero or more:

many :: f -> f [a]

if defined, some , many should least solutions of equations:

some v = (:) <$> v <*> many v  many v = v <|> pure []

i couldn't find instance some , many defined. what meaning , practical use? used @ all? i've been unable grasp purpose definition.

update: i'm not asking alternative, some , many

i tend see them in applicative parser combinator libraries.

a :: parser [string] = (string "hello")

and see many used purpose in default definitions of parsing in parsers.

i think parsec being primary example of parser combinator library hides use of some/many since redefines things (<|>).


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