Parslet makes developing complex parsers easy. It does so by

  • providing the best error reporting possible

  • not generating reams of code for you to debug

Parslet takes the long way around to make your job easier. It allows for incremental language construction. Often, you start out small, implementing the atoms of your language first; parslet takes pride in making this possible.

Eager to try this out? Please see the associated web site:


require 'parslet'
include Parslet

# parslet parses strings
  parse('foo') # => "foo"@0

# it matches character sets
match['abc'].parse('a') # => "a"@0
match['abc'].parse('b') # => "b"@0
match['abc'].parse('c') # => "c"@0

# and it annotates its output
  parse('foo') # => {:important_bit=>"foo"@0}

# you can construct parsers with just a few lines
quote = str('"')
simple_string = quote >> (quote.absent? >> any).repeat >> quote

  parse('"Simple Simple Simple"') # => "\"Simple Simple Simple\""@0

# or by making a fuss about it 
class Smalltalk < Parslet::Parser
  root :smalltalk

  rule(:smalltalk) { statements }
  rule(:statements) { 
    # insert smalltalk parser here (outside of the scope of this readme)

# and then'smalltalk')


This library should work with most rubies. I've tested it with MRI 1.8 (except 1.8.6), 1.9, rbx-head, jruby. Please report as a bug if you encounter issues.

Note that due to Ruby 1.8 internals, Unicode parsing is not supported on that version.

On Mac OS X Lion, ruby-1.8.7-p352 has been known to segfault. Use ruby-1.8.7-p334 for better results.


At version 1.4.0 - See HISTORY.txt for changes.

© 2010, 2011, 2012 Kaspar Schiess