Formula evaluation with adjacent parentheses incorrect

[FrittenKeeZ]

Having a formula with division followed by adjacent parentheses statements is evaluated incorrectly.

Example:

(2*4+3)+9(4+1)/(1*9)(5+7)
(2*4+3)+9*(4+1)/(1*9)*(5+7)

Both of these formulas should evaluate to 71, but only the last one does.

[josdejong]

Thanks for your input. Implicit multiplications can be tricky. A simpler case of your example is the following:

math.parse('1/(2)(4)') // 0.125

I agree that the behavior is quite confusing. Mathjs has some special rules in place dealing with implicit multiplication. The difficult thing is that in different cases, you would expect different types of behavior. Just giving implicit multiplication the same precedence as multiply and divide gives odd cases too.

math.parse('1/(2)(x)').toString({ parenthesis: 'all' }) // "1 / (2 x)" 
math.parse('1/2 x').toString({ parenthesis: 'all' })    // "(1 / 2) x"
math.parse('4km / 2h').toString({ parenthesis: 'all' }) // "(4 km) / (2 h)" 

I'm always open for good ideas to improve the behavior, but implicit multiplication is a tricky subject, see for example #792, #2370.

[FrittenKeeZ]

@josdejong we're using these regexes to "fix" the expressions before evaluation:

expression
    .replace(/(\d)(\()/, '$1*$2')
    .replace(/(\))(\d)/, '$1*$2')
    .replace(/(\))(\()/, '$1*$2')

[josdejong]

Thanks for sharing.

Please be careful with regexes like these, they can go wrong when you have nesting, like nested parenthesis inside parenthesis.

In general, it can help to present to the user how the experession is evaluated by shoing the exrpesion with all the (relevant) parens.

[FrittenKeeZ]

It's looking specifically for something like 5(, )5 and )( - anything else is untouched, so nesting shouldn't be a problem.