Can't represent this equation with mathjs: a + b = b + a

[ashleydavis]

Hi, Mathjs is awesome.

I'm having a problem with a particular equation that Mathjs doesn't seem to support.

I need to use the AST produced, here's some example code:

const rootNode = math.parse("a + b = b + a");

I get this error:

Uncaught SyntaxError: Invalid left hand side of assignment operator = (char 7)
    at createSyntaxError (parse.js:1682)
    at parseAssignment (parse.js:638)
    at parseBlock (parse.js:553)
    at parseStart (parse.js:523)
    at parse (parse.js:69)
    at Object.parse (typed-function.js:1085)

Is there a way to have Mathjs handle this type of equation? Or is it just not supported?

Thanks!

[josdejong]

Such equations are indeed not supported. It will be supported when we add support for a solver I think, see #38, though there is no one working on this yet.

[ChristopherChudzicki]

The error message offers a clue: "Invalid left hand side of assignment operator =". The single equals sign is assignment, not equality. I think you'll get what you want if you use double equals:

const rootNode = math.parse("a + b == b + a")

Then you should be able to manipulate the parse tree.

[ashleydavis]

@josdejong I've made a copy of mathjs code and I've modified it produce a 'binary operator' instead of the normal assigment node. That fits my need and it was easy to update the code to work the way I wanted. Thanks for your effort on this.

@ChristopherChudzicki Thanks for the advice Chris, I'm actually making a maths visualizer be used by non-programers so I can't rely on them understanding the difference between = and ==.

My maths visualizer simplifies a formula and shows the working out. Just a fun little project to help people understand how algebraic transformations work. Once it's finished I'll send you a link!

[josdejong]

👍

[josdejong]

will close this issue now, feel free to reopen if needed. Sharing your visualizer would be cool of course :)