[Haskell-cafe] [Alternative] some/many narrative

[Chris Wong]

> Okay, so how about the following as a user narrative for some and many?
>
> ...

I was in the middle of writing my own version of Applicative when I
stumbled on this intense debate. Here's what I wrote for the
documentation:

class (Applicative f, Monoid f) => Alternative f where
    -- | Keep repeating the action (consuming its values) until it
fails, and then return the values consumed.
    --
    -- [Warning]: This is only defined for actions that eventually fail
    -- after being performed repeatedly, such as parsing. For pure values such
    -- as 'Maybe', this will cause an infinite loop.
    some :: f a -> f [a]
    some v = ...

    -- | Similar to 'many', but if no values are consumed it returns
'empty' instead of @f []@.
    --
    -- [Warning]: This is only defined for actions that eventually fail
    -- after being performed repeatedly, such as parsing. For pure values such
    -- as 'Maybe', this will cause an infinite loop.
    many :: f a -> f [a]
    many v = ...

Warnings are repeated for emphasis :)