Piwo

Piwo is the front half of a language implementation, written by hand in Java. Source text goes through a lexer into tokens, and a recursive-descent parser turns those tokens into an abstract syntax tree that can be serialized to JSON.

The grammar covers variables, functions, arrays, control flow, expressions and comments. The keywords are Serbian beer brands, which is the joke, but the error reporting is not: lexical and syntax errors are reported with line and column tracking.

This is a front end. It produces an AST, not a running program.

Recursive-descent parsing is straightforward until the error cases. Reporting a syntax error usefully means keeping accurate line and column information through the lexer and into every AST node, so a message can point at the character that broke rather than at the statement that contained it.

• 01Hand-written lexer
• 02Recursive-descent parser
• 03Abstract syntax tree generation
• 04Variables, functions and arrays
• 05Control flow and expressions
• 06Comments
• 07Serbian beer-themed keyword set
• 08Lexical error handling
• 09Syntax error handling
• 10Line and column tracking
• 11JSON serialization of the generated AST