Add committed-operator

Signed-off-by: Mattias Andrée <m@maandree.se>

1 files changed, 15 insertions, 3 deletions

diff --git a/libparser.7 b/libparser.7
index 7157769..2d921a7 100644
--- a/libparser.7
+++ b/libparser.7
@@ -88,6 +88,7 @@ integer          = _decimal | _hexadecimal; (* May not exceed 255. *)
 _low             = character | integer;
 _high            = character | integer;
 
+committed        = \(dq+\(dq, _, _operand;
 rejection        = \(dq!\(dq, _, _operand;
 concatenation    = _operand, {_, \(dq,\(dq, _, _operand};
 alternation      = concatenation, {_, \(dq|\(dq, _, concatenation};
@@ -100,7 +101,7 @@ embedded-rule    = identifier;
 
 _literal         = char-range | exception | string;
 _group           = optional | repeated | group | embedded-rule;
-_operand         = _group | _literal | rejection;
+_operand         = _group | _literal | rejection | committed;
 
 _expression      = alternation;
 
@@ -135,6 +136,15 @@ have no semantic meaning and are useful only to put a
 alternation inside a concatenation without creating a
 new rule for that.
 .PP
+The parser is non-deterministic, which can make it really
+slow. The speed up parsing, you can add commits. Once the
+committed sentence has been matched, the branching-points
+inside it are unrecorded, so when the parser backtracks,
+it will not try different choices inside the committed
+sentence. Commit sentences are undone by the parser when
+it backtracks to a branching-point outside the committed
+sentence.
+.PP
 In character ranges, the
 .B _high
 and
@@ -150,12 +160,14 @@ the rules will appear in the tree-formatted result.
 .PP
 Left recursion is illegal (it will cause stack
 overflow at runtime as the empty condition before the
-recursion is always met).
+recursion is always met). Likewise, repeated optional
+sentences are illegal; a repeated sentence must always
+consume input, otherwise it gets stuck.
 
 .SS Right-context-sensitive grammar
 libparser originally used context-free grammar, but with
 introduction of the rejection rule, specifically the ability
-to reject a rejection, it became a phrase for
+to reject a rejection, it became a parser for
 right-context-sensitive grammar which is a grammar that is
 that can generate any context-sensitive language, it is
 however weakly equivalent to context-sensitive grammar.