jac-core-cheatsheet

Jac match statements use colon plus indented case bodies, not braces. Writing `case 0 { ... }` is a parse error (E0001). Guards like `case int() as n if n < 0:` and destructuring patterns for sequences, dicts, and classes work as in Python.

Plain module imports take a semicolon (`import os;`) while selective brace imports take none (`import from math { pi }`). No-dot imports resolve from the project root at any depth, while dotted relative imports are mainly for client code resolved by the bundler.

E0030 occurs when a brace import ends with a semicolon, such as `import from X { Y };`. Remove the trailing semicolon; only plain module imports like `import X;` require one.

No. Python reserved words cannot name `has` fields or parameters even with backtick escaping, failing with E0067. Jac-only keywords like `visit` or `node` can be escaped with a single leading backtick.

Jac warns on any unused bound name, including validation-only bindings. Prefix intentionally unused names with underscore, discard values with `_ = expr;`, or drop the exception binding with `except ValueError { ... }`.

No, Jac has no `pass` statement and using one raises E0010. Write empty braces `{}` for an intentionally empty block instead.