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Added initial support for recursive expressions.

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Updated docs and tests accordingly.

[SVN r54994]
This commit is contained in:
John Maddock
2009-07-17 10:23:50 +00:00
parent 02a629baf7
commit 5a6bc29d7c
44 changed files with 1013 additions and 264 deletions
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27
doc/syntax_perl.qbk
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@ -511,6 +511,17 @@ are typically used to improve performance; only the best possible match
for pattern will be considered, if this doesn't allow the expression as a
whole to match then no match is found at all.
[h5 Recursive Expressions]
[^(?['N]) (?-['N]) (?+['N]) (?R) (?0)]
=(?R)= and =(?0)= recurse to the start of the entire pattern.
[^(?['N])] executes sub-expression /N/ recursively, for example =(?2)= will recurse to sub-expression 2.
[^(?-['N])] and [^(?+['N])] are relative recursions, so for example =(?-1)= recurses to the last sub-expression to be declared,
and =(?+1)= recurses to the next sub-expression to be declared.
[h5 Conditional Expressions]
=(?(condition)yes-pattern|no-pattern)= attempts to match /yes-pattern/ if
@ -519,9 +530,21 @@ the /condition/ is true, otherwise attempts to match /no-pattern/.
=(?(condition)yes-pattern)= attempts to match /yes-pattern/ if the /condition/
is true, otherwise fails.
/condition/ may be either a forward lookahead assert, or the index of
/condition/ may be either: a forward lookahead assert, the index of
a marked sub-expression (the condition becomes true if the sub-expression
has been matched).
has been matched), or an index of a recursion (the condition become true if we are executing
directly inside the specified recursion).
Here is a summary of the possible predicates:
* [^(?(?\=assert)yes-pattern|no-pattern)] Executes /yes-pattern/ if the forward look-ahead assert matches, otherwise
executes /no-pattern/.
* =(?(?!assert)yes-pattern|no-pattern)= Executes /yes-pattern/ if the forward look-ahead assert does not match, otherwise
executes /no-pattern/.
* =(?(R)yes-pattern|no-pattern)= Executes /yes-pattern/ if we are executing inside a recursion, otherwise
executes /no-pattern/.
* [^(?(R['N])yes-pattern|no-pattern)] Executes /yes-pattern/ if we are executing inside a recursion to sub-expression /N/, otherwise
executes /no-pattern/.
[h4 Operator precedence]