I have this small example of an ambiguous grammar that doesn’t return the result I’m expecting:

module Test

exports
context-free start-symbols
Exp
context-free syntax
Id			-> Exp {cons(“Exp2Id”)}
Exp "+" Exp -> Exp {left, cons("Plus")}
ID			-> Id {cons("Id")}

lexical syntax
[A-Z][a-zA-Z0-9]*		-> VarId
[a-zA-Z][a-zA-Z0-9_]*	-> ID
context-free syntax
VarId	 	-> Id		{cons(“Id2Var”)}
VarId	 	-> Exp		{cons(“Exp2Var”)}

This is the returned AST for “A+B”:

amb(
[ amb(
[Exp2Var(“A”), Exp2Id(amb([Id2Var(“A”), Id(“A”)]))]
)
, amb(
[Exp2Var(""), Exp2Id(amb([Id2Var(““), Id(””)]))]
)
]
)

“A” is parsed correctly, but “B” is missing.
Am I doing something wrong, or is this a JSGLR error? I really need the correct parsing, with all of the ambiguities.

Submitted by Radu Mereuta on 18 May 2011 at 14:56

This seems to be a problem with the new ambiguity handling approach, not the imploder. Maartje, could you take a look? The internal representation shows the following ambiguity:

[amb([regular(aprod(278),[regular(aprod(285),[regular(aprod(286),[65, regular(aprod(270),[])])])]), regular(aprod(282),[amb([regular(aprod(279),[regular(aprod(285),[regular(aprod(286),[65, regular(aprod(270),[])])])]), regular(aprod(280),[regular(aprod(283),[regular(aprod(284),[65, regular(aprod(261),[])])])])])])]), regular(aprod(259),[]), regular(aprod(257),[43]), regular(aprod(259),[]), amb([regular(aprod(278),[regular(aprod(285),[regular(aprod(286),[66, regular(aprod(270),[])])])]), regular(aprod(282),[amb([regular(aprod(279),[regular(aprod(285),[regular(aprod(286),[66, regular(aprod(270),[])])])]), regular(aprod(280),[regular(aprod(283),[regular(aprod(284),[66, regular(aprod(261),[])])])])])])])]

(Note the different ParseProductionNode characters in the branches!)

bug in left associativity filter fixed