Tokenizer (or Expression) should fail on nonsensical input

[AlexeyMK]

One example of an expression that should fail is 5 4 - two values (or identifiers) not connected with an operator of any sort. This seems like a good cause for a stricter grammar / lexer.

[rubysolo]

This would fail at evaluation:

calculator.evaluate!('10 7')
RuntimeError: no rule matched {{10 7}}

Do you feel that it should fail when attempting to construct the expression?

[AlexeyMK]

Yeah - ideally this should be a compile-time error and not a run-time error. This is particularly important in my case, where non-technical users write formulas that only get run days later when the formulas are run. It is substantially less painful for debugging if I can tell them there's an error when they write it than when the formula gets run.

My current work-around is to calculate dependencies, mark all the identifiers with the value 0, and run the formula to see if it passes.

[lawso017]

+1 for this suggestion, or would it be reasonable to expose a parse!() method that could be called to validate a formula?

[rikkipitt]

I was looking for this functionality too, specifically to help validate expressions saved in a model. I came up with this custom validator:

https://gist.github.com/rikkipitt/4551c9b72b35cd7a4756

Please try it out and extend if your case requires!

Rikki

[rubysolo]

This is fixed in v2.0 -- calculator.ast(expression) will return an AST node or raise a parse error.