Contents

# A more complex parser that illustrates how a compiler might be constructed.
# The parser recognizes strings and integer literals and constructs almost a
# useful AST from the file contents. 

require 'pp'

$:.unshift '../lib/'
require 'parslet'

include Parslet

class LiteralsParser < Parslet::Parser
  rule :space do
    (match '[ ]').repeat(1)
  end
  
  rule :literals do
    (literal >> eol).repeat
  end
  
  rule :literal do
    (integer | string).as(:literal) >> space.maybe
  end
  
  rule :string do
    str('"') >> 
    (
      (str('\\') >> any) |
      (str('"').absnt? >> any)
    ).repeat.as(:string) >> 
    str('"')
  end
  
  rule :integer do
    match('[0-9]').repeat(1).as(:integer)
  end
  
  rule :eol do
    line_end.repeat(1)
  end
  
  rule :line_end do
    crlf >> space.maybe
  end
  
  rule :crlf do
    match('[\r\n]').repeat(1)
  end

  root :literals
end

parsetree = LiteralsParser.new.parse(
  File.read('simple.lit'))
  
class Lit < Struct.new(:text)
  def to_s
    text.inspect
  end
end
class StringLit < Lit
end
class IntLit < Lit
  def to_s
    text
  end
end

transform = Parslet::Transform.new do
  rule(:literal => {:integer => simple(:x)}) { IntLit.new(x) }
  rule(:literal => {:string => simple(:s)}) { StringLit.new(s) }
end
  
ast = transform.apply(parsetree)
pp ast

Version data entries

3 entries across 3 versions & 1 rubygems

Version	Path
parslet-1.1.1	example/string_parser.rb
parslet-1.1.0	example/string_parser.rb
parslet-1.0.1	example/string_parser.rb