Grammar with low-precedence postfix operator?

I'm trying to write an ANTLR4 grammar for a language with a low precedence
postfix operator (Wolfram Language with '&', but I use a simple toy grammar
below). I'm struggling with finding the right pattern to express this
language.


Consider my (incorrect) grammar below that parses math expressions:


<snip>
grammar MathExpression;


//Parser Rules
term
: INT
| '(' expr ')' //parentheses
| <assoc=right> term '^' term //exponentiation
| term term //implicit multiplication
;


expr
: term
| ('+' | '-') expr //unary plus/minus
| expr ('/' | '*') expr //division and explicit multiplication
| expr ('+' | '-') expr //addition/subtraction
| expr '++' //increment
;


//Lexer Rules
INT : [0-9]+ ;
WS : [ \t\r\n]+ -> skip ;
<snip>


The problem with this grammar is that the generated parser chokes on, for
example, the input '2++^3', as '^' cannot follow '++' in this grammar. If I
get rid of implicit multiplication I can collapse the grammar into a single
rule that parses the language I am wanting, but I don't want to give up
implicit multiplication.


What's the pattern for this situation?


Incidentally, this is my first post to this group, and I am charmed to see
several authors of my textbooks among the members here.


Best,


Robert

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