Grammar Rules
A grammar rule has the form:
(nonterm -> (right-hand side items) semantics)nonterm is a nonterminal symbol that is the left-hand side of the production; the rule says that the left-hand side nonterminal can be composed of the sequence of items on the right-hand side.
The allowable items on the right-hand side are:
| word | exactly the specified word |
| (nonterminal) | like a subroutine call to a sub-grammar. |
| (category) | a word in the category, e.g. (month) |
| (number) | any number |
| (symbol) | any symbol |
| ? | preceding item is optional |
| (separate ? from a word by a space) | |
The semantics is clojure code to be executed when the grammar rule is satisfied. The right-hand side items are available as variables $1, $2, $3, etc., similar to what is done in Yacc. For example, consider the rule:
(loc -> (in (city)) (restrict 'city $2))In this case, $2 refers to whatever matches the (city) part of the grammar rule.