Class: Parslet::Expression

Inherits:
Object
  • Object
show all
Includes:
Parslet
Defined in:
lib/parslet/expression.rb

Overview

Allows specifying rules as strings using the exact same grammar that treetop does, minus the actions. This is on one hand a good example of a fully fledged parser and on the other hand might even turn out really useful.

This can be viewed as an extension to parslet and might even be hosted in its own gem one fine day.

Defined Under Namespace

Classes: Treetop

Instance Method Summary collapse

Methods included from Parslet

any, exp, included, match, sequence, simple, str, subtree

Constructor Details

#initialize(str, opts = {}, context = self) ⇒ Expression

Creates a parslet from a foreign language expression.

Example: 

Parslet::Expression.new("'a' 'b'")



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# File 'lib/parslet/expression.rb', line 20

def initialize(str, opts={}, context=self)
  @type = opts[:type] || :treetop
  @exp = str
  @parslet = transform(
    parse(str))
end

Instance Method Details

#parse(str) ⇒ Object

Parses the string and returns a parse tree.



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# File 'lib/parslet/expression.rb', line 41

def parse(str)
  parser = Treetop::Parser.new
  parser.parse(str)
end

#to_parslet ⇒ Object

Turns this expression into a parslet.



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# File 'lib/parslet/expression.rb', line 48

def to_parslet
  @parslet
end

#transform(tree) ⇒ Object

Transforms the parse tree into a parslet expression.



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# File 'lib/parslet/expression.rb', line 29

def transform(tree)
  transform = Treetop::Transform.new
  
  # pp tree
  transform.apply(tree)
rescue 
  warn "Could not transform: " + tree.inspect
  raise
end