Controlling parser rule alternatives precedence - antlr

Question

I have an expression IF 1 THEN 2 ELSE 3 * 4. I want this parsed as IF 1 THEN 2 ELSE (3 * 4), however using my grammar (extract) below, it parses it as (IF 1 THEN 2 ELSE 3) * 4.
formula: expression EOF;
expression
: LPAREN expression RPAREN #parenthesisExp
| IF condition=expression THEN thenExpression=expression ELSE elseExpression=expression #ifExp
| left=expression BINARYOPERATOR right=expression #binaryoperationExp
| left=expression op=(TIMES|DIV) right=expression #muldivExp
| left=expression op=(PLUS|MINUS) right=expression #addsubtractExp
| left=expression op=(EQUALS|NOTEQUALS|LT|GT) right=expression #comparisonExp
| left=expression AMPERSAND right=expression #concatenateExp
| NOT expression #notExp
| STRINGLITERAL #stringliteralExp
| signedAtom #atomExp
;
My understanding is that because I have the ifExp alternative appearing before the muldivExp it should use that first, then because I have the muldivExp before atomExp (which handles numbers) it should do 3 * 4 to end the ELSE, rather than using just the 3. In which case I can't see why it's making the IF..THEN..ELSE a child of the multiplication.
I don't think the rest of the grammar is relevant here, but in case it is see below for the whole thing.
grammar AnaplanFormula;
formula: expression EOF;
expression
: LPAREN expression RPAREN #parenthesisExp
| IF condition=expression THEN thenExpression=expression ELSE elseExpression=expression #ifExp
| left=expression BINARYOPERATOR right=expression #binaryoperationExp
| left=expression op=(TIMES|DIV) right=expression #muldivExp
| left=expression op=(PLUS|MINUS) right=expression #addsubtractExp
| left=expression op=(EQUALS|NOTEQUALS|LT|GT) right=expression #comparisonExp
| left=expression AMPERSAND right=expression #concatenateExp
| NOT expression #notExp
| STRINGLITERAL #stringliteralExp
| signedAtom #atomExp
;
signedAtom
: PLUS signedAtom #plusSignedAtom
| MINUS signedAtom #minusSignedAtom
| func_ #funcAtom
| atom #atomAtom
;
atom
: SCIENTIFIC_NUMBER #numberAtom
| LPAREN expression RPAREN #expressionAtom // Do we need this?
| entity #entityAtom
;
func_: functionname LPAREN (expression (',' expression)*)? RPAREN #funcParameterised
| entity LSQUARE dimensionmapping (',' dimensionmapping)* RSQUARE #funcSquareBrackets
;
dimensionmapping: WORD COLON entity; // Could make WORD more specific here
functionname: WORD; // Could make WORD more specific here
entity: QUOTELITERAL #quotedEntity
| WORD+ #wordsEntity
| left=entity DOT right=entity #dotQualifiedEntity
;
WS: [ \r\n\t]+ -> skip;
/////////////////
// Fragments //
/////////////////
fragment NUMBER: DIGIT+ (DOT DIGIT+)?;
fragment DIGIT: [0-9];
fragment LOWERCASE: [a-z];
fragment UPPERCASE: [A-Z];
fragment WORDSYMBOL: [#?_£%];
//////////////////
// Tokens //
//////////////////
IF: 'IF' | 'if';
THEN: 'THEN' | 'then';
ELSE: 'ELSE' | 'else';
BINARYOPERATOR: 'AND' | 'and' | 'OR' | 'or';
NOT: 'NOT' | 'not';
WORD: (DIGIT* (LOWERCASE | UPPERCASE | WORDSYMBOL)) (LOWERCASE | UPPERCASE | DIGIT | WORDSYMBOL)*;
STRINGLITERAL: DOUBLEQUOTES (~'"' | ('""'))* DOUBLEQUOTES;
QUOTELITERAL: '\'' (~'\'' | ('\'\''))* '\'';
LSQUARE: '[';
RSQUARE: ']';
LPAREN: '(';
RPAREN: ')';
PLUS: '+';
MINUS: '-';
TIMES: '*';
DIV: '/';
COLON: ':';
EQUALS: '=';
NOTEQUALS: LT GT;
LT: '<';
GT: '>';
AMPERSAND: '&';
DOUBLEQUOTES: '"';
UNDERSCORE: '_';
QUESTIONMARK: '?';
HASH: '#';
POUND: '£';
PERCENT: '%';
DOT: '.';
PIPE: '|';
SCIENTIFIC_NUMBER: NUMBER (('e' | 'E') (PLUS | MINUS)? NUMBER)?;

Answer 1

Move your ifExpr down near the end of your alternatives. (In particular, below any alternative that you would wish to match your elseExpression
Your “if ... then ... else ...” is below the muldivExp precisely because you've made it a higher priority. Items lower in the tree are evaluated before items higher in the tree, so higher priority items belong lower in the tree.
With:
expression:
LPAREN expression RPAREN # parenthesisExp
| left = expression BINARYOPERATOR right = expression # binaryoperationExp
| left = expression op = (TIMES | DIV) right = expression # muldivExp
| left = expression op = (PLUS | MINUS) right = expression # addsubtractExp
| left = expression op = (EQUALS | NOTEQUALS | LT | GT) right = expression # comparisonExp
| left = expression AMPERSAND right = expression # concatenateExp
| NOT expression # notExp
| STRINGLITERAL # stringliteralExp
| signedAtom # atomExp
| IF condition = expression THEN thenExpression = expression ELSE elseExpression = expression #
ifExp
;
I get