I have been using my PonderTalk (Smalltalk like) language for a while now
and I have just noticed that leaving a block empty causes a parser error.
This is with ANTLRWorks 1.2.3. I have refined the grammar to show the point.
The problem line is ^(statements). With that taken out the parsing works.
grammar Trial;
options {
output = AST;
k = 2;
}
start : sentences EOF
;
sentences
: sentence? (DOT sentences)?
-> sentence? sentences?
;
sentence: WORD | block;
block : '[' sentences ']'
-> ^(sentences)
;
WORD : LETTER LETTER+;
LETTER : 'a'..'z';
DOT : '.';
The following input works as expected:
hello. [ block ]. goodbye
The following just terminates the parser after processing the ']' with no
AST being produced at all:
hello. [ ] . goodbye
There are no errors. However with my PonderTalk parser I get
Exception thrown: rule sentences
org.antlr.runtime.tree.RewriteEmptyStreamException: rule sentences
at org.antlr.runtime.tree.RewriteRuleElementStream._next(
RewriteRuleElementStream.java:158)
at org.antlr.runtime.tree.RewriteRuleElementStream.nextTree(
RewriteRuleElementStream.java:145)
at net.ponder2.parser.PonderTalkParser.block(PonderTalkParser.java:1061)
at net.ponder2.parser.PonderTalkParser.object(PonderTalkParser.java:693)
at net.ponder2.parser.PonderTalkParser.objectMessage(
PonderTalkParser.java:470)
at net.ponder2.parser.PonderTalkParser.sentence(PonderTalkParser.java:323)
at net.ponder2.parser.PonderTalkParser.sentence(PonderTalkParser.java:341)
at net.ponder2.parser.PonderTalkParser.sentences(PonderTalkParser.java:194)
at net.ponder2.parser.PonderTalkParser.start(PonderTalkParser.java:129)
at net.ponder2.parser.P2Compiler.parse(P2Compiler.java:495)
at net.ponder2.parser.P2Compiler.parse(P2Compiler.java:440)
at net.ponder2.ShellInstance.doPonderTalk(ShellInstance.java:211)
at net.ponder2.ShellInstance.run(ShellInstance.java:163)
at java.lang.Thread.run(Thread.java:613)
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