Is it good practice to throw exceptions in parsing functions

Question

I basically read across the entire internet that exceptions are bad, slow and should be avoided whenever possible. This confuses me because I thought I have a "valid" case to use exceptions.

Consider an input parser which transforms a string into an expression tree, that a calculator can evaluate. For me this seems perfectly suited for exceptions, see the following Pseudo-Code

try:
    expression_tree = input_parser.parse(user_input);

    print "Result: " , calculator.evaluate(expression_tree);

catch division_by_zero e:
    print "Error: Division by zero near: " , e.code_window();

catch matrix_dimension e:
    print "Error: Matrix dimension don't match near: ", e.code_window();

catch ...

Since I do not plan to fix the error, just catch it and then ask for a new input, the speed factor should be of no concern. Furthermore this makes the code well readable and easy to handle, as I don't need error codes or manual jumps / premature exits from functions. But as I've stated, the overall attitude towards exceptions makes me doubt myself.

Answer 1

There are no shortage of complaints about throwing and catching both within the same method.  These are considered a form of goto, considered harmful.

Throwing an exception when we don't want to proceed — e.g. with parsing — is different and is reasonable usage of exceptions.

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However, in your code you might abstract the exceptions a bit by making one root exception, say, an abstract parse_error class with a method to print itself.  Your parser will then have a bit more flexibility in generating error messages, and your outer handler won't have to check for all the specific exceptions.  (Of course, division by zero shouldn't happen in the parser — if it does then the parser is really more than that, like an interpreter, or possibly an optimizer.)

Answer 2

Exceptions should be used for exceptional cases. A parse error is not exceptional; an input that can be parsed correctly is probably more exceptional: -(