From: Robert Feldt <feldt@...>
Date: 2003-09-24T07:34:07+09:00
Subject: Re: Is Rockit abandoned?

> I guess what I'm looking for is something like:
>
> * here is a source file we must parse where regular expressions would be
> too big a pain (or impossible)
> * here is a grammar
> * here is a parser
> * here's how it all works together
>
Would examples like this be helpful:

# Rockit Tutorial example number X
#
# NOTE that the API and behavior below is not fixed but the current
# design/view of how Rockit 0.6 will work.
#

# We want to parse brace-delimited balanced string literals like:

input_example = "%{1{2}3}"

# which should return the parsed string "1{2}3".
# This is hard to do with regexps (although I'm sure there is some
# special notation added that makes it possible!).

# In Rockit we can write a grammar for this like:

require 'rockit'

g = <<EOG
 StringLiteral -> '%{' CurlyInner '}'.       StringLiteral[inner]
 CurlyInner    =  Balanced*
 Balanced      =  '{' Balanced* '}'
               |  /[^{}]/
EOG

grammar = Rockit::Grammar.new g

# generate a parser class from the grammar
parser_class = grammar.generate_parser_class

# instantiate a parser
parser = parser_class.new

# then parse
p parser.parse(input_example) # => StringLiteral['1{2}3']

# Note that Rockit by default builds an Abstract Syntax Tree (AST)
# for you by creating and calling an AstBuilder. If you want to # change how the AST is built or even not build an AST you can define
# your own builder:

class MyBuilder < parser_class.default_builder_class
  # Name of method is lower_case version of the AST name specified
  # in the grammar above.
  def string_literal(inner)
    inner
  end
end

# now specify that your builder should be used by a parser
parser2 = parser_class.new MyBuilder.new

p parser2.parse(input_example) # => '1{2}3'

?

/Robert