Content deleted Content added
→Computational model: New section |
→Definition: Added top of section |
||
Line 29:
== Definition ==
{{No footnotes|section|date=December 2022}}
A '''parsing expression''' is a kind of pattern that each string may either '''match''' or '''not match'''. In case of a match, there is a unique prefix of the string (which may be the whole string, the empty string, or something in between) which has been ''consumed'' by the parsing expression; this prefix is what one would usually think of as having matched the expression. However, whether a string matches a parsing expression ''may'' (because of look-ahead predicates) depend on parts of it which come after the consumed part. A '''parsing expression language''' is a set of all strings that match some specific parsing expression.<ref name="For04" />{{rp|Sec.3.4}}
A '''parsing expression grammar''' is a collection of named parsing expressions, which may reference each other. The effect of one such reference in a parsing expression is as if the whole referenced parsing expression was given in place of the reference. A parsing expression grammar also has a designated '''starting expression'''; a string matches the grammar if it matches its starting expression.
=== Syntax ===
Formally, a parsing expression grammar consists of:
| |||