parslet.rb

Path: lib/parslet.rb
Last Update: Fri Jul 15 14:35:39 -0400 2016

A simple parser generator library. Typical usage would look like this:

  require 'parslet'

  class MyParser < Parslet::Parser
    rule(:a) { str('a').repeat }
    root(:a)
  end

  pp MyParser.new.parse('aaaa')   # => 'aaaa'@0
  pp MyParser.new.parse('bbbb')   # => Parslet::Atoms::ParseFailed:
                                  #    Don't know what to do with bbbb at line 1 char 1.

The simple DSL allows you to define grammars in PEG-style. This kind of grammar construction does away with the ambiguities that usually comes with parsers; instead, it allows you to construct grammars that are easier to debug, since less magic is involved.

Parslet is typically used in stages:

The first stage is traditionally intermingled with the second stage; output from the second stage is usually called the ‘Abstract Syntax Tree’ or AST.

The stages are completely decoupled; You can change your grammar around and use the second stage to isolate the rest of your code from the changes you‘ve effected.

Further reading

All parslet atoms are subclasses of {Parslet::Atoms::Base}. You might want to look at all of those: {Parslet::Atoms::Re}, {Parslet::Atoms::Str}, {Parslet::Atoms::Repetition}, {Parslet::Atoms::Sequence}, {Parslet::Atoms::Alternative}.

When things go wrong

A parse that fails will raise {Parslet::ParseFailed}. This exception contains all the details of what went wrong, including a detailed error trace that can be printed out as an ascii tree. ({Parslet::Cause})

Required files

parslet/slice   parslet/cause   parslet/source   parslet/atoms   parslet/pattern   parslet/pattern/binding   parslet/transform   parslet/parser   parslet/error_reporter   parslet/scope  

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