[antlr-interest] BETA Grammar

[Kyle Robson]

Hi all, I have a grammar here that is giving me a null pointer
exception when I try to use the ANTLR tool on it. It's too large, and
there's so much going on, that I don't know where to begin debugging
it. I assume I may have some common problem that I need to fix
throughout.

The grammar is based off the book here:
http://www.daimi.au.dk/~beta/Books/index.html#betabook_download

My (very straightforward) implementation of it is here:
http://paste-it.net/public/qac33be/

Here's the full text in case that link dies:

grammar Beta;
options {
    output=AST;
    ASTLabelType=CommonTree; // type of $stat.tree ref etc...
}

//BetaForm:   ( stat {System.out.println($stat.tree.toStringTree());} )+ ;
Beta:   ( BetaForm {System.out.println($BetaForm.tree.toStringTree());} )+ ;
BetaForm:	DescriptorForm
	|	AttributesForm
	;
DescriptorForm
	:	ObjectDescriptor
	;
AttributesForm
	:	Attributes
	;
ObjectDescriptor
	:	SuperPatternOpt MainPart
	;
MainPart:	'(#' Attributes ActionPart '#)'
	;
Attributes
	:	(AttributeDeclOpt)+
	;
SuperPatternOpt
	:	(SuperPattern)?
	;
SuperPattern
	:	AttributeDenotation
	;
AttributeDeclOpt: 	(AttributeDecl)?
	;
AttributeDecl
	:	PatternDecl
	|	SimpleDecl
	|	RepetitionDecl
    ;

PatternDecl
	:	Names ':' ObjectDescriptor -> Names ':' ObjectDescriptor
	;

SimpleDecl
	:	Names ':' ReferenceSpecification -> Names ':' ReferenceSpecification
	;

RepetitionDecl
	:	Names ':' '[' Index ']' ReferenceSpecification
	;

ReferenceSpecification
	:	StaticItem
	|	DynamicItem
	|	StaticComponent
	|	DynamicComponent
	;
StaticItem
	:	'@' ObjectSpecification -> '@' ObjectSpecification
	;
DynamicItem
	:	'^' AttributeDenotation
	;
StaticComponent
	:	'@'
	|	ObjectSpecification
	;
DynamicComponent
	:	'^'
	|	AttributeDenotation
	;
ObjectSpecification
	:	ObjectDescriptor
	|	AttributeDenotation
	;
Index	:	SimpleIndex
	|	NamedIndex
	;
NamedIndex
	:	NameDcl ':' Evaluation
	;
ActionPart
	:	EnterPartOpt DoPartOpt ExitPartOpt
	;
EnterPartOpt
	:	(EnterPart)?
	;
EnterPart
	:	'enter' Evaluation
	;
DoPartOpt
	:	(DoPart)?
	;
DoPart	:	'do' Imperatives
	;
ExitPartOpt
	:	(ExitPart)?
	;
ExitPart:	'exit' Evaluation;
Imperatives
	:	(ImpOpt ';')+
	;
ImpOpt	:	(Imp)?
	;
Imp	:	LabelledImp
	|	LabelledCompoundImp
	|	ForImp
	|	IfImp
	|	LeaveImp
	|	RestartImp
	|	InnerImp
	|	SuspendImp
	|	Evaluation
	;
LabelledImp
	:	NameDcl ':' Imp
	;
LabelledCompoundImp
	:	'(' NameDcl Imperatives NameDcl ')'
	;
ForImp	:	'(for' Index 'repeat' Imperatives 'for)'
	;
IfImp	:	'(if' Evaluation Alternatives ElsePartOpt 'if)'
	;
Alternatives
	:	(Alternative)+
	;
Alternative
	:	Selections 'then' Imperatives
	;
Selections
	:	Selection
	;
Selection
	:	CaseSelection
	;
CaseSelection
	:	'//' Evaluation
	;
ElsePartOpt
	:	(ElsePart)?
	;
ElsePart:	'else' Imperatives
	;
LeaveImp:	'leave' NameApl
	;
RestartImp
	:	'restart' NameApl
	;
InnerImp:	'inner' NameAplOpt
	;
NameAplOpt
	:	(NameApl)?
	;
SuspendImp
	:	'suspend'
	;
Evaluations
	:	(Evaluation ',')+
	;
Evaluation
	:	Expression
	|	AssignmentEvaluation
	;
AssignmentEvaluation
	:	Evaluation '->' Transaction
	;
Transaction
	:	ObjectEvaluation
	|	ComputedObjectEvaluation
	| 	ObjectReference
	| 	EvalList
	| 	StructureReference
	;
ObjectEvaluation
	:	InsertedItem
	| 	Reference
	;
Reference
	:	ObjectDenotation
	| 	DynamicObjectGeneration
	;
DynamicObjectGeneration
	:	DynamicItemGeneration
	|	DynamicComponentGeneration
	;
InsertedItem
	:	ObjectDescriptor
	;
ObjectDenotation
	:	AttributeDenotation
	;
ComputedObjectEvaluation
	:	ObjectEvaluation '!'
	;
ObjectReference
	:	Reference '[]'
	;
StructureReference
	:	AttributeDenotation '##'
	;
EvalList:	'(' Evaluations ')'
	;
DynamicItemGeneration
	:	'&' ObjectSpecification
	;
DynamicComponentGeneration
	:	'&' | ObjectSpecification;
AttributeDenotation
	:	NameApl
	|	Remote
	|	ComputedRemote
	|	Indexed
	|	ThisObject
	;
Remote	:	AttributeDenotation '.' NameApl
	;
ComputedRemote
	:	'(' Evaluations ')' '.' NameApl
	;
Indexed	:	AttributeDenotation '[' Evaluation ']'
	;
ThisObject
	:	'this' '(' NameApl ')'
	;
Expression
	:	RelationalExpr
	|	SimpleExp
	;
RelationalExpr
	:	EqExp
	|	LtExp
	|	LeExp
	|	GtExp
	|	GeExp
	|	NeExp
	;
SimpleExp
	:	AddExp
	|	SignedTerm
	|	Term
	;
AddExp	:	PlusExp
	|	MinusExp
	|	OrExp
	;
SignedTerm
	:	UnaryPlusExp
	|	UnaryMinusExp
	;
Term	:	MulExp
	|	Factor
	;
MulExp	:	TimesExp
	|	DivExp
	|	ModExp
	|	AndExp
	;
EqExp	:	SimpleExp '=' SimpleExp;
LtExp	:	SimpleExp '<' SimpleExp;
LeExp	:	SimpleExp '<=' SimpleExp;
GtExp	:	SimpleExp '>' SimpleExp;
GeExp	:	SimpleExp '>=' SimpleExp;
NeExp	:	SimpleExp '<>' SimpleExp;
PlusExp	:	SimpleExp '+' Term;
MinusExp:	SimpleExp '-' Term;
OrExp	:	SimpleExp 'or' Term;
UnaryPlusExp
	:	'+' Term;
UnaryMinusExp
	:	'-' Term;
TimesExp:	Term '*' Factor;
DivExp	:	Term 'div' Factor;
ModExp	:	Term 'mod' Factor;
AndExp	:	Term 'and' Factor;
Factor	:	TextConst
	|	IntegerConst
	|	NotExp
	|	NoneExp
	|	RepetitionSlice
	|	Transaction
	;
RepetitionSlice
	:	AttributeDenotation '[' Evaluation ':' Evaluation ']'
	;
NotExp	:	'not' Factor;
NoneExp	:	'none';
Names	:	(NameDcl)+;
NameDcl	:	NameDecl;
NameApl	:	NameAppl;
SimpleEntry
	:	(TextConst)?
	;
TextConst
	:	String
	;
IntegerConst
	:	Int
	;
SimpleIndex
	:	Evaluation
	;
NameAppl:	NameDecl;
NameDecl:	(Letter|'_')+(Digit|Letter|'_')*
	;

String	:	'\''Char*'\''
	;
//           where <char> can be any char except "'" and newline.
//                        "'" are allowed in <String>, iff preceeded with "\".
//                        "\n", "\t", etc. are allowed in <String> to
//                        represent non-printable chars - see Compiler
//                        manual (mia91-02) for details.

Const	:	(Int|Based)//|Real)
	;
//  	  where
Int	:	 (Digit)+
	;
Based	:	Int('X'|'x')BasedNum
	;
BasedNum:	(Digit|Letter)+
	;
//Real	:	Int['.' Int][('E'|'e')[('+'|'-')]Int]
//	;

Letter	:	'a'..'z'|'A'..'Z'
	;
Digit	:	'0'..'9'
	;
Char	:	'0'..'9'|'a'..'z'|'A'..'Z'|'!'|'@'|'#'|'$'|'%'|'^'|'&'|'*'|'('|')'|'-'|'='|'_'|'+'|'['|']'|'{'|'}'|'|'|'\\'|';'|':'|'\''|'<'|'>'|','|'.'|'/'|'?'
	;
	
WS  :   (' '|'\t'|'\r'|'\n')+ {skip();} ;

Sincere thanks for any tips,

Kyle