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

[Thomas Schilling]

On 15 December 2011 06:29, Chris Wong <chrisyco+haskell-cafe at gmail.com> wrote:

> class (Applicative f, Monoid f) => Alternative f where
>    -- | Keep repeating the action (consuming its values) until it
> fails, and then return the values consumed.

I think this should be "collect" rather than "consume" and you can
omit the parentheses.  I also think that we should include the
original definition, which is more formally precise (although it could
use with some examples).

>    --
>    -- [Warning]: This is only defined for actions that eventually fail

Perhaps add the remark that we expect non-deterministic actions.

>    -- 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 :)
>
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