| form | meaning | form | meaning |
|---|---|---|---|
| (p,r) | rule: rewrite p as r | (,) | empty pattern: halt |
| rules are tried top to bottom | halts also when no rule matches | ||
| first rule that matches fires, on its leftmost occurrence | ($,...) | a pattern that never occurs is a comment | |
| after a rewrite, scanning restarts from the top | text outside parentheses is ignored |