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')


* Tools for every part of the parser chain
* Transformers generate Abstract Syntax Trees
* Accelerators transform parsers, making them quite a bit faster
* Pluggable error reporters
* Graphviz export for your parser
* Rspec testing support rig
* Simply Ruby, composable and hackable


This library is intended to work with Ruby variants >= 1.9. I've tested it on MRI 1.9, rbx-head, jruby. Please report as a bug if you encounter issues.


Production worthy.

© 2010-2017 Kaspar Schiess