Treetop (parser)

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

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

Written on July 16, 2020, Last update on July 23, 2020

ruby parser