Basic arithmetic grammar -- handling parentheses-CodePudding

I have written the following to handle basic binary operations in arithmetic:

grammar Calc;

expression
    : OPERAND (BIN_OP expression)*
    ;

// 12 or .12 or 2. or 2.38
OPERAND
    : [0-9]  ('.' [0-9]*)?
    | '.' [0-9] 
    ;

BIN_OP
    : [- /*]
    ;

Now I can do things like:

0.9 2.4*3.6

However, how is order-of-operations and parentheses normally handled with antlr? For example:

What if I wanted to write (0.9 2.4)*3.6 instead, how could I do that?
Or, what if I wanted to write ((0.9 2.4)*3.6) ?
And finally, to catch an invalid case of un-matched parens, (((((0.9 2.4)*3.6)) ?

How is that normally handled in antlr?

CodePudding user response：

One of the really nice things that ANTLR4 brought was the ability to easily represent precedence by the ordering of alternatives in a rule.

Try something like:

grammar Calc;

expression
    : '(' expression ')' # parenExpr
    : expression (MUL_OP | DIV_OP) expression # mulDivExpr
    : expression (ADD_OP | SUB_OP) expressions # addSubExpr
    : OPERAND # operandExpr
    ;

// 12 or .12 or 2. or 2.38
OPERAND
    : [0-9]  ('.' [0-9]*)?
    | '.' [0-9] 
    ;

SUB_OP: '-';
ADD_OP: ' ';
DIV_OP: '/';
MUL_OP: '*';
    ;