Parslet example of transforms with default values

example.rb

require 'pp'
require 'parslet'

module Example # as in 'lots of insipid and stupid parenthesis'
  class Parser < Parslet::Parser

	rule(:ws)			{ match('[\s]').repeat(1) }
    rule(:ws?)			{ ws.maybe }
	  rule(:number)		{ match('[0-9]').repeat(1) }
    rule(:offset) 		{ ws? >> str("[") >> number.as(:offset) >> str("]")  }
    rule(:format_code) 	{ ws? >> str("d").as(:code) >> ws? }
    rule(:format) 		{ (offset.maybe >> format_code).as(:format) }
  
    root(:format)
  end

  class Transform < Parslet::Transform
    rule(:code => simple(:x)) 	                    { {:o=>"0", :c=>x} }
	  rule(:offset=> simple(:o),:code => simple(:c))  { {:o=>o,:c=>c} }
  end
end

parser = Example::Parser.new
transform = Example::Transform.new
[
  "    d",
  "  [2] d ",
  "     [3]   d "].each do |pexp|
  begin
    result = parser.parse(pexp)
	puts result.inspect
    puts "String: \"#{pexp}\" Result: #{result.inspect} Transformed: #{transform.apply(result)}"
  rescue Parslet::ParseFailed => m
    puts "String: \"#{pexp}\" Error: #{m}"
  end
  puts
end

example2.rb

require 'pp'
require 'parslet'

module Example # as in 'lots of insipid and stupid parenthesis'
  class Parser < Parslet::Parser
    rule(:ws)			{ match('[\s]').repeat(1) }
    rule(:ws?)			{ ws.maybe }
    rule(:number)		{ match('[0-9]').repeat(1).as(:number) }
    rule(:offset) 		{ (ws? >> str("[") >> number >> str("]")) }
    rule(:format_code) 	        { ws? >> str("d").as(:code) >> ws? }
    rule(:format) 		{ (offset.maybe.as(:offset_val).as(:offset) >> format_code).as(:format) }
  
    root(:format)
  end

  class Transform < Parslet::Transform
	rule({:number => simple(:i)})	                        { i.to_i }
	rule({:offset_val => simple(:v)})	                { v || 5 }
	rule(:format=>{:offset=>simple(:o), :code=>simple(:c)}) { "Format #{c.to_s*o}" }
  end
end

parser = Example::Parser.new
transform = Example::Transform.new

[	"    d",
	"  [2] d ",
	"     [3]   d ",
].each do |pexp|
  begin
    result = parser.parse(pexp)
    puts result.inspect
    puts "String: \"#{pexp}\" \n  Result: #{result.inspect}\n  Transformed: #{transform.apply(result)}"
  rescue Parslet::ParseFailed => m
    puts "String: \"#{pexp}\" Error: #{m}"
  end
  puts
end