Question

I know the AST I want to make (I think), which is:

 ^( STATEMENT alias ( FOREACH rel ( FOREACH_PLAN_SIMPLE ( GENERATE STAR ) ) ) )

so I added the following rule:

realias_statement : alias EQUAL rel SEMI_COLON
                 -> ^( STATEMENT alias ( FOREACH rel ( FOREACH_PLAN_SIMPLE ( GENERATE STAR ) ) ) )
;

However, when I try to compile this, I get the following errors…

 [java] error(100): src//org/apache/pig/parser/QueryParser.g:174:49: syntax error: antlr: MismatchedTokenException(73!=69)
 [java] error(100): src//org/apache/pig/parser/QueryParser.g:174:51: syntax error: antlr: NoViableAltException(75@[])
 [java] error(100): src//org/apache/pig/parser/QueryParser.g:174:95: syntax error: antlr: NoViableAltException(69@[])
 [java] error(100): src//org/apache/pig/parser/QueryParser.g:174:97: syntax error: antlr: NoViableAltException(69@[])
 [java] error(100): src//org/apache/pig/parser/QueryParser.g:174:99: syntax error: antlr: NoViableAltException(69@[])
 [java] error(100): src//org/apache/pig/parser/QueryParser.g:0:1: syntax error: assign.types: MismatchedTreeNodeException(0!=18)
 [java] error(10):  internal error: src//org/apache/pig/parser/QueryParser.g : java.lang.NullPointerException
 [java] org.antlr.grammar.v3.DefineGrammarItemsWalker.countAltsForRule(DefineGrammarItemsWalker.java:153)
 [java] org.antlr.grammar.v3.DefineGrammarItemsWalker.rule(DefineGrammarItemsWalker.java:1546)
 [java] org.antlr.grammar.v3.DefineGrammarItemsWalker.rules(DefineGrammarItemsWalker.java:1190)
 [java] org.antlr.grammar.v3.DefineGrammarItemsWalker.grammarSpec(DefineGrammarItemsWalker.java:623)
 [java] org.antlr.grammar.v3.DefineGrammarItemsWalker.grammar_(DefineGrammarItemsWalker.java:275)
 [java] org.antlr.tool.Grammar.defineGrammarSymbols(Grammar.java:748)
 [java] org.antlr.tool.CompositeGrammar.defineGrammarSymbols(CompositeGrammar.java:369)
 [java] org.antlr.Tool.process(Tool.java:465)
 [java] org.antlr.Tool.main(Tool.java:93)

I will of course continue to dig into what these errors mean, but I was wondering more general if this sort of thing can be done? IE I know exactly how I want it to look, but am not sure how to get it to look like that.

Thanks

Answer 1

Assuming STATEMENT, FOREACH, FOREACH_PLAN_SIMPLE and GENERATE STAR are defined in the tokens { ... } section, this should work:

realias_statement
 : alias EQUAL rel SEMI_COLON
   -> ^(STATEMENT alias ^(FOREACH rel ^(FOREACH_PLAN_SIMPLE ^(GENERATE STAR))))
 ;

Note the ^ before the opening parenthesis.