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aarongough · Oct 15, 2010 · 2e581b7 · timcharper · Jul 5, 2012 · aarongough
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diff --git a/Readme.rdoc b/Readme.rdoc
@@ -0,0 +1,55 @@
+= Treetop S-Expression Parser
+
+This is a very small & simple demonstration parser built using {Treetop}[http://treetop.rubyforge.org/]. It is meant solely to teach the very basics of implementing a grammar in Treetop, not as an actual parser for S-Expressions (which is why it's not packaged as a gem, and why it has no tests).
+
+A real parser *should* improve in several main areas:
+
+* Test coverage: Unit tests are vital for parsers.
+* Performance: This example is slow in the extreme compared to simpler parsing methods, a real parser should be performant.
+* Error reporting: Even the best written parser is a complete pain if it doesn't have intelligent error reporting.
+
+=== The Core Grammar
+
+For easy reference the core grammar of the parser is reproduced here:
+
+  grammar Sexp
+
+    rule expression
+      space? '(' body ')' space? <Expression>
+    end
+
+    rule body
+      (expression / identifier / float / integer / string / space )* <Body>
+    end
+
+    rule integer
+      ('+' / '-')? [0-9]+ <IntegerLiteral>
+    end
+
+    rule float
+      ('+' / '-')? [0-9]+ (('.' [0-9]+) / ('e' [0-9]+)) <FloatLiteral>
+    end
+
+    rule string
+      '"' ([^"\\] / "\\" . )* '"' <StringLiteral>
+    end
+
+    rule identifier
+      [a-zA-Z\=\*] [a-zA-Z0-9_\=\*]* <Identifier>
+    end
+
+    rule space
+      [\s]+
+    end
+
+  end
+
+=== More Info
+
+For more info visit the {Treetop website}[http://treetop.rubyforge.org/], and have a read through the source-code of this parser (don't worry, there isn't much of it!).
+
+=== Author & Credits
+
+Author:: {Aaron Gough}[mailto:aaron@aarongough.com]
+
+Copyright (c) 2010 {Aaron Gough}[http://thingsaaronmade.com/] ({thingsaaronmade.com}[http://thingsaaronmade.com/]), released under the MIT license
diff --git a/node_extensions.rb b/node_extensions.rb
@@ -0,0 +1,37 @@
+module Sexp
+  class IntegerLiteral < Treetop::Runtime::SyntaxNode
+    def to_array
+      return self.text_value.to_i
+    end
+  end
+
+  class StringLiteral < Treetop::Runtime::SyntaxNode
+    def to_array
+      return eval self.text_value
+    end
+  end
+
+  class FloatLiteral < Treetop::Runtime::SyntaxNode
+    def to_array
+      return self.text_value.to_f
+    end
+  end
+
+  class Identifier < Treetop::Runtime::SyntaxNode
+    def to_array
+      return self.text_value.to_sym
+    end
+  end
+
+  class Expression < Treetop::Runtime::SyntaxNode
+    def to_array
+      return self.elements[0].to_array
+    end
+  end
+
+  class Body < Treetop::Runtime::SyntaxNode
+    def to_array
+      return self.elements.map {|x| x.to_array}
+    end
+  end
+end
diff --git a/parser.rb b/parser.rb
@@ -0,0 +1,30 @@
+require 'treetop'
+
+require File.expand_path(File.join(File.dirname(__FILE__), 'node_extensions.rb'))
+
+class Parser
+
+  Treetop.load(File.expand_path(File.join(File.dirname(__FILE__), 'sexp_parser.treetop')))
+  @@parser = SexpParser.new
+
+  def self.parse(data)
+    tree = @@parser.parse(data)
+
+    if(tree.nil?)
+      raise Exception, "Parse error at offset: #{@@parser.index}"
+    end
+
+    self.clean_tree(tree)
+
+    return tree.to_array
+  end
+
+  private
+
+    def self.clean_tree(root_node)
+      return if(root_node.elements.nil?)
+      root_node.elements.delete_if{|node| node.class.name == "Treetop::Runtime::SyntaxNode" }
+      root_node.elements.each {|node| self.clean_tree(node) }
+    end
+
+end
diff --git a/sexp_parser.treetop b/sexp_parser.treetop
@@ -0,0 +1,31 @@
+grammar Sexp
+
+  rule expression
+    space? '(' body ')' space? <Expression>
+  end
+
+  rule body
+    (expression / identifier / float / integer / string / space )* <Body>
+  end
+
+  rule integer
+    ('+' / '-')? [0-9]+ <IntegerLiteral>
+  end
+
+  rule float
+    ('+' / '-')? [0-9]+ (('.' [0-9]+) / ('e' [0-9]+)) <FloatLiteral>
+  end
+
+  rule string
+    '"' ([^"\\] / "\\" . )* '"' <StringLiteral>
+  end
+
+  rule identifier
+    [a-zA-Z\=\*] [a-zA-Z0-9_\=\*]* <Identifier>
+  end
+
+  rule space
+    [\s]+
+  end
+
+end