8.12
2 Grammars
| (require yaragg/base/grammar) | package: yaragg |
A grammar is a formal description of the syntax of a language. Grammars consist of a start symbol and a set of production rules which describe how to rewrite the start symbol into valid strings in the language. Grammars are used to construct parsers, which can transform input strings into a parse tree structured according to the rules laid out in the grammar.
A predicate for grammars.
procedure
(grammar #:rules rules #:start-symbol start-symbol) → grammar? rules : (sequence/c production-rule?) start-symbol : nonterminal-symbol?
Constructs a grammar containing rules and using start-symbol to identify the
initial rules to apply during parsing.
2.1 Production rules
A production rule is a rule in a grammar that describes how a nonterminal symbol in the grammar can be rewritten into a string of other grammar symbols and input tokens. The rewrite pattern is represented by a production expression.
procedure
(production-rule? v) → boolean?
v : any/c
A predicate for production rules.
procedure
(production-rule #:nonterminal nonterminal #:substitution substitution #:action action) → production-rule? nonterminal : nonterminal-symbol? substitution : production-expression? action : semantic-action?
Constructs a production rule that rewrites nonterminal into substitution.
During parsing, action is applied to parse nodes created by the constructed rule.