Re: Parsing expressions without outer parentheses

> expression: simple_expression | expression '=' simple_expression;
> simple_expression: term | simple_expression '+' term;
> term: factor | term '*' factor;
> factor: primary | factor '^' primary;
> primary: constant | '(' expression ')';
>
> Now I want to accept only expressions which are not completely
> enclosed in a pair of parentheses, e.g. `(1) + (2)' would be
> accepted, but `(1 + 2)' would not.


Seems like this could be handled semantically. If an expression begins
with an open parenthesis, and the parentheses nesting level does not
drop to zero before the end of the expression, then "error: outer
parentheses." You need another production to delimit the
expression. Something like


expression : {action} inner_expression {action} ;


And then change expression to inner_expression in the grammar fragment shown
above.


http://parsers.org

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