Treetop is a Ruby library that allows you to create parsers easily by describing them using a Parsing Expression Grammar (PEG). - A quick intro

see also

• Visualizing Packrat Parsing
• Understanding parser combinators: a deep dive - Scott Wlaschin

Home (still alive)

• performance are good compared to other

Doc / Tutorials

• A quick intro
• Turning a parse tree into an abstract syntax tree (AST)
  • filtering parse tree to get an ast
    • Treetop’s Confusing Behavior
    • class vs module - use rule ( subrule1 / subrule2 ) <class object> see 1
      • treetop will inject several definition so using module is more general and adviced, see 2

rule foo; 	a <A_In_Foo> / b <B_In_Foo>; end

rule a; 	something <A>;	end

rule b;	something_else <B>; end

In the case where “foo” matches “something_else”, the SyntaxNode for “something_else” will have two mixed-in modules (both “B” and “B_In_Foo”). Use parentheses around a list of alternates if you want to mix in the same module regardless of which possibility is matched.

• Treetop: Typical Errors
  • error reporting à la clang
  • Matching whitespaces
  • prevent AST squashing: use 1..1
• Doc
  • Semantic Interpretation
    • Methods Available on Treetop::Runtime::SyntaxNode - elements elements of the matched sequence
    • labels: for subexpression, like citrus
  • Syntactic Recognition
    • c like comment grammar
  • keywords - Striping spaces in a SQL parser
    • keywords must not be immediately followed by a symbol character. I use negative lookahead for this.
    • The top rule consumes leading whitespace, then almost every rule consumes following whitespace (this is my policy). You should test your grammar with minimum and maximum whitespace.
  • Advanced Techniques
    • Matching a Keyword But Not Words Prefixed Therewith
• Debugging
  • using in ruby
    • parser options: start from a different rule / continue
    • debugging option
    • AST guideline
    • Advanced Grammar debugging
      • Generating grammar, and instrumenting code
• google groups (2018)
  • custom data for syntax node => his is a significant weakness in the design of Treetop. I made a custom proxy for the “input” and attached my Context to it. You might get away with doing something similar
• Ruby Conference 2007 Treetop: Syntactic Analysis with Ruby by Nathan Sobo

Some treetop example

• Clifford Heath CQL
• my sql grammar POC sql
• A “grue”some look at Statemachine and Treetop

Alternatives

• parslet
  • compared to other
  • Get started
  • Stack Traces in Parslet
• whittle ?
  • Whittle: the new, powerful, easy-to-use Parser on the ruby block (all ruby, all the time, based on the LALR(1) algorithm)
• rexical / racc
  • example sql-parser - sqlite-parser (js)
• Why you should not use (f)lex, yacc and bison (ANTLR)