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Simplify and document non-greedy behavior in processAcceptConfigs

This commit is contained in:
Sam Harwell 2012-10-16 07:51:47 -05:00
parent fb87e4c785
commit 1af9b4c338
1 changed files with 39 additions and 25 deletions
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52
runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNSimulator.java
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@ -409,11 +409,39 @@ public class LexerATNSimulator extends ATNSimulator {
reach, prevAccept.config, prevAccept.index);
}
/* Non-greedy handling works by removing all non-greedy configurations
* from reach when an accept state is reached for the same token. For
* example, consider the following two tokens:
*
* BLOCK : '{' .* '}';
* OPTIONAL_BLOCK : '{' .* '}' '?';
*
* With the following input:
*
* {stuff}?
*
* After matching '}', an accept state at the end of BLOCK is reached,
* so any configurations inside the non-greedy .* loop in BLOCK will be
* removed from reach. The configuration(s) inside the non-greedy .*
* loop in OPTIONAL_BLOCK are unaffected by this because no
* configuration is in an accept state for OPTIONAL_BLOCK at this input
* symbol.
*/
BitSet altsAtAcceptState = new BitSet();
BitSet nonGreedyAlts = new BitSet();
LexerATNConfig acceptConfig = null;
for (ATNConfig config : reach) {
if (config.state instanceof RuleStopState) {
altsAtAcceptState.set(config.alt);
if ( debug ) {
System.out.format("processAcceptConfigs: hit accept config %s index %d\n",
config, input.index());
}
if (acceptConfig == null) {
acceptConfig = (LexerATNConfig)config;
}
}
if (!((LexerATNConfig)config).isGreedy()) {
@ -423,20 +451,13 @@ public class LexerATNSimulator extends ATNSimulator {
}
nonGreedyAlts.and(altsAtAcceptState);
// this is now "alts with at least one non-greedy config and one accept config"
if (!nonGreedyAlts.isEmpty()) {
reach.removeNonGreedyConfigsInAlts(nonGreedyAlts);
}
for (int ci=0; ci<reach.size(); ci++) {
LexerATNConfig c = (LexerATNConfig)reach.get(ci);
if ( c.state instanceof RuleStopState) {
if ( debug ) {
System.out.format("processAcceptConfigs: hit accept config %s index %d\n",
c, input.index());
}
int index = input.index();
if ( index > prevAccept.index ) {
// mark the new preferred accept state
if (acceptConfig != null && input.index() > prevAccept.index) {
if ( debug ) {
if ( prevAccept.index>=0 ) {
System.out.println("processAcceptConfigs: found longer token");
@ -444,17 +465,10 @@ public class LexerATNSimulator extends ATNSimulator {
}
// condition > not >= will favor prev accept at same index.
// This way, "int" is keyword not ID if listed first.
traceAcceptState(c.alt);
if ( debug ) {
System.out.format("markExecSettings for %s @ index=%d, line %d:%d\n", c, index, prevAccept.line, prevAccept.charPos);
}
captureSimState(prevAccept, input, c);
traceAcceptState(acceptConfig.alt);
captureSimState(prevAccept, input, acceptConfig);
}
// move to next char, looking for longer match
// (we continue processing if there are states in reach)
}
}
return reach;
}