test.rb

require 'whittle'

class Parser < Whittle::Parser
  class StringParser < Whittle::Parser
    rule('"')

    rule(:esc => /\\./).as { |esc| eval('"' + esc + '"') }

    rule(:chars => /[^\\"]+/)

    rule(:body) do |r|
      r[:body, :esc].as   { |body, esc|   body << esc }
      r[:body, :chars].as { |body, chars| body << chars }
      r[:esc]
      r[:chars]
    end

    rule(:string) do |r|
      r['"', :body, '"'].as { |_, body, _| body }
    end

    start(:string)
  end


  rule(:wsp => /\s+/).skip!

  rule("(")
  rule(")")
  rule(",")

  rule(:identifier => /[a-zA-Z_][a-zA-Z0-9_]*/)

  rule(:string => /"(\\.|[^"\\]+)*"/).as { |str| StringParser.new.parse(str) }

  rule(:expr) do |r|
    r[:invocation]
    r[:string]
  end

  rule(:args) do |r|
    r[:args, ",", :expr].as { |args, _, expr| args << expr }
    r[:expr].as             { |expr| [expr] }
  end

  rule(:invocation) do |r|
    r[:identifier, "(", :args, ")"].as { |id, _, args, _| { :invocation => id, :args => args } }
  end

  start(:expr)
end

require 'pp'
pp Parser.new.parse('foo("   string with some spaces and \\" an escape \\\\ here")')