TatSu

At least for the people who send me mail about a new language that they’re designing, the general advice is: do it to learn about how to write a compiler. Don’t have any expectations that anyone will use it, unless you hook up with some sort of organization in a position to push it hard. It’s a lottery, and some can buy a lot of the tickets. There are plenty of beautiful languages (more beautiful than C) that didn’t catch on. But someone does win the lottery, and doing a language at least teaches you something.

Dennis Ritchie (1941-2011) Creator of the C programming language and of Unix

TatSu is a tool that takes grammars in a variation of EBNF as input, and outputs memoizing (Packrat) PEG parsers in Python.

Why use a PEG parser? Because regular languages (those parsable with Python’s re package) “cannot count”. Any language with nested structures or with balancing of demarcatiors requires more than regular expressions to be parsed.

TatSu can compile a grammar stored in a string into a tatsu.grammars.Grammar object that can be used to parse any given input, much like the re module does with regular expressions, or it can generate a Python module that implements the parser.

TatSu supports left-recursive rules in PEG grammars, and it honors left-associativity in the resulting parse trees.