Allow options in Parslet::ClassMethods.parse

[RyanScottLewis]

This pull request allows options to be passed to the rule class method as well as specs to prove that they are working correctly.

Options

---

:predicate

If true, it defines another rule with the atom .maybe attached to it.

Without

rule(:space) { str(' ') }
rule(:space?) { space.maybe }

With

rule(:space, predicate: true) { str(' ') }

---

:repeat

If true, it defines another rule with the atom .repeat(1) attached to it.

Without

rule(:space) { str(' ') }
rule(:spaces) { space.repeat(1) }

With

rule(:space, repeat: true) { str(' ') }

If a Hash is passed, it allows for extra options to be passed:

:min and :max

These allow a developer to set the min and max repeat arguments on the "repeated" rule.

Without

rule(:space) { str(' ') }
rule(:spaces) { space.repeat(3, 5) }

With

rule(:space, repeat: { min: 3, max: 5 }) { str(' ') }

:predicate

If true, it defines another "repeated" rule with the atom .maybe attached to it.

Without

rule(:space) { str(' ') }
rule(:spaces) { space.repeat(1) }
rule(:spaces?) { spaces.maybe }

With

rule(:space, repeat: { min: 3, max: 5, predicate: true }) { str(' ') }

[kschiess]

Hi Ryan,

Thanks for the PR & for using parslet!

I don't think the rule API needs extending. What you're proposing can very simply be achieved by something like

def self.maybe_rule name, rule
   define_method name do 
      self.send(rule).maybe
   end
end

rule(:space) { ... }
maybe_rule(:space?, :space)

Obviously this can be extended and made to look exactly like what you're proposing. My point here is: This doesn't add to parslet except sugar - and I am trying to keep things simple and give everyone one way of doing things.

If you look at projects from people that work with parslet (the doc page has a list) - nearly everyone is doing a small amount of meta-programming not unlike the example above to make things easier - but not everyone's metaprogramming looks the same - which is why I don't include it in parslet itself.

In a way, parslets API is unwieldy on purpose - it's also pure Ruby and very hackable - I encourage people to extend parslet for their projects!

Also, I am trying to keep Rails out of parslet ;) That includes methods with options and activesupport. Not every Rubyist likes the Rails style of doing things.

I hope this makes sense to you. If you would like discuss extensions to parslet, I would like to welcome you to our mailing list - it is where an extension like this one might receive the support that it needs to make it past my critical eye. Also - keep the contributions coming, I actually merge from time to time ;)

regards, kaspar

[RyanScottLewis]

Sounds good, I'll make a gem which will allow devs to mixin this functionality using modules and leave the choice up to them.

This was my original plan, but I figured I would shoot this pull request out there and see what would come of it. :+1:

Cheers, -- Ryan