Class: DParse::Parsers::Alt

Inherits:
DParse::Parser show all
Defined in:
lib/d-parse/parsers/combinators/alt.rb

Instance Method Summary collapse

Methods inherited from DParse::Parser

#apply, #bind, #capture, #compact, #expectation_message, #first, #flatten, #ignore, #map, #match?, #second, #select_even, #select_odd, #to_s

Constructor Details

#initialize(*parsers) ⇒ Alt

Returns a new instance of Alt.



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# File 'lib/d-parse/parsers/combinators/alt.rb', line 4

def initialize(*parsers)
  # FIXME: ensure >0 parsers are provided
  @parsers = parsers
end

Instance Method Details

#inspect ⇒ Object 



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# File 'lib/d-parse/parsers/combinators/alt.rb', line 27

def inspect
  "alt(#{@parsers.map(&:inspect).join(',')})"
end

#read(input, pos) ⇒ Object 



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# File 'lib/d-parse/parsers/combinators/alt.rb', line 9

def read(input, pos)
  init = DParse::Failure.new(input, DParse::Position::FAR_BEHIND)
  @parsers.reduce(init) do |old_res, parser|
    case old_res
    when DParse::Success
      old_res
    when DParse::Failure
      new_res = parser.read(input, pos)
      case new_res
      when DParse::Success
        new_res.with_best_failure(old_res)
      when DParse::Failure
        [old_res, new_res].max_by { |r| r.pos.index }
      end
    end
  end
end