Writing Treetop rule to parse input in any order

Question

I'm looking for a way to write Treetop rules which will find some values in any order. So:

rule top
  # ?
end    

rule gender
  ('women'/'men') / ''
end

rule age_under
  ('under' age) / ''
end

rule age
  [0-9]+
end

I would like to parse these inputs:

"women under 10"
"under 10 women"
"under 10"
"women"

How can I achieve this ? Thanks

Answer 1

Here's an example of parsing in any order. The only trouble is you would have to handle duplicates by hand since Treetop doesn't have a rule for unordered-non-repeating elements.

rule top
 ((gender / age_under) ' '?)*
end

rule gender
 'women' / 'men'
end

rule age_under
 'under ' age
end

rule age
 [0-9]+
end