2.3*(3+--4) gives "SyntaxError: Value expected (char 9)" about mathjs

[josdejong]

Thanks. not sure how often this happens in practice (2 - -3 ok, but 2 - --3?). Anyway it is a valid mathematical expression so the parser should be just happy to evaluate it for us.

[jmichae3]

I had to think - If I were writing a parser, how would I do a BNF for this?
unarysign::= '+' | '-'
unarysigns::= unarysign | unarysigns
not sure how that nil would enter into this.
but it's been 20 years and my compiler book isn't the best. would like one that isn't just a textbook or has the answers and good examples. I wouldn't mind a multi-volume set, because that's about what it takes to do a good job covering it, otherwise it's just handwaving.

[jmichae3]

it could also be things like 2+-+-+-+-5 (just for fun)

[josdejong]

Ha ha, you seem to be looking for ways to create art from math expressions, like ASCII art ;)