Eliminate/move class Alternative

[Wolfgang Jeltsch]

Am Sonntag, 15. März 2009 23:50 schrieb Ben Franksen:
> This is mostly due to the class method 'empty'.
>
> First of all, this is a bad name, /especially/ in the context of parsers,
> where 'empty' intuitively means 'recognize the empty sequence of tokens'
> which is definitely /not/ what Alternative's 'empty' means. (Indeed, this
> is normally be the meaning of 'pure' from class Applicative.)
>
> The 'empty' from Alternative rather means 'fail'. Yeah, I know that this
> name is already taken by class Monad. Many names would be better
> than 'empty', for instance 'none', or just 'failed'. (I'll stick
> with 'none' in what follows.)

The parser fails so “fail” might be a good name. However, when using an 
applicative style for writing parsers (in contrast to the “imperative” do 
notation), you almost write a grammar of your language. And “empty” just 
denotes the empty language. So the name might be not as bad as it first looks 
like.

Best wishes,
Wolfgang