📝Grammar

This page will cover (for the most part) how to add your own grammars.

Warning: Creating new grammar for Cosmo is a process.

1. Check the current syntax types to make sure any tokens you want to include in your grammar are already being lexed.

   • If a token you want to include in your grammar is not in the list of syntax types, you will need to create your own syntax type and lex it. Lexing a syntax is straightforward, and you should be able to figure it out without a tutorial.

2. Figure out what your expression/statement should be represented as. Are you adding an operator? Then you can just match your syntax in a binary operator parsing method (like parse_additive, including parse_var_declaration as well as parse_assignment) or if it's unary, the parse_unary method. Otherwise:

   • Create an AST node and a parser method. Naming is straightforward, your AST node should be named what it represents. The parsing method should be named parse_(node_name). For example if you added an if statement, the node's file would be called if.cr, the node's class would be called If, and the parsing method would be called parse_if_statement. Don't forget to include the visit_nodename_expr/visit_nodename_stmt method in Expression/Statement's Visitor abstract class. In the case of the if statement, it would be called visit_if_stmt.

3. Implement the visit_nodename_expr/visit_nodename_stmt method into the interpreter, and perform all necessary actions for your grammar.

4. Implement the visit_nodename_expr/visit_nodename_stmt into the resolver, and resolve any nodes associated with your new node.