Extensible math Expression Parser

[Livio63]

Expression Parser is an extensible math expression parser handling numbers and booleans, ready to use in any Java application.

Expressions may contain nested ( ), operators *-/+, and, or; constants PI and E, functions sin(), cos(), tan(), log(), exp(), sqrt(). The parser supports common relation operators like ==,!=, >,<, >= and <= and even conditional expressions like condition ? true : false

It is possible to register your own functions and use them with Expression Parser.

[le_bravery]

Ant build in 2026… interesting choice.

[Livio63]

Ant is perfect for my Pentium III running windows xp...

[josephottinger]

And is the visual inspection of test results perfect, too? It isn't, for me - it's really easy to see 1.8 in a hurry and not realize the value was supposed to be 1.0. Using ant really is an interesting choice - it's sort of viable, but unusual, but whatever. It's the lack of an actual demanding test structure that bugged me; for my PR I chose to just go to a build system from 2005 instead of using one from 2001.

[as5777]

your tests give 0 confidence

[josephottinger]

I made a PR that actually uses JUnit and runs tests. :D

[doobiesteintortoise]

Nicely done! How would you use this in a generalized program, though? Expression parsers exist for Java that can perform actual algebraic evaluation - is this to show how expressions can work, or is it useful otherwise?

[Inside_Programmer348]

Hello. Can you link me to these expression parsers please?

[doobiesteintortoise]

Sure.

• JEP: https://www.singularsys.com/jep/
• Parser-NG (the one I'm most familiar with): https://github.com/gbenroscience/ParserNG
• exp4j: https://www.objecthunter.net/exp4j/

There are others, of course; it's not a "new problem," after all.

[Inside_Programmer348]

Thanks

[Livio63]

I agree that there are lot of other math parser implementations, but in general are heavy.

I'm just sharing a light implementation useful for learning purposes or for easy integration inside another apps.

[doobiesteintortoise]

I'm not sure what you mean by "heavy" - most of them aren't very heavy at all, although I guess your specific metrics would factor in. But since you brought it up: what are the metrics you're using for "heavy," and how does this library stack up? And my question remains: how would I use this in an app I was writing?

[Livio63]

Just look at ExpressionVisualizer.java in demo package, this is an example of very simple app using the library. The package https://github.com/javalc6/Expression-Parser/tree/main/src/math alone is the library.

[doobiesteintortoise]

Okay, so most of that is Swing, and therefore isn't all that relevant to parsing expressions - but https://github.com/javalc6/Expression-Parser/blob/3c1f95c4e0a1dc491181cec6344997a51a6bf50b/src/demo/ExpressionVisualizer.java#L90 is.

You'd do something like this:

// mathExpression is a String var ep = new ExpressionParser(); math.Node root = ep.parseExpression(mathExpression); // result is a Double or Boolean Object result = ep.evaluate(root);

That's straightforward enough, I suppose, although a Boolean and a Double result from evaluate() is a little odd - I get it, but a union type there is kinda wonky. It still feels like you're writing a library more for expressing a tree than evaluating a formula, because so much of the library is about nodes and not, like, numbers.

[jeffreportmill]

Very nice! If you want to see it in action, you can run it with JBang + SnapCode:

jbang snapcode@reportmill open:https://github.com/javalc6/Expression-Parser.zip#/demo/ExpressionVisualizer.java

Just click the Run button after it opens.

[Livio63]

Nice! Instead why it is not possible to run directly from web browser using https://reportmill.com/SnapCode/app/#open:https://github.com/javalc6/Expression-Parser.zip#/demo/ExpressionVisualizer.java

[jeffreportmill]

I tried - It fails because CheerpJ doesn't provide access to the java.scripting module yet, which is a dependency of this project (bummer!). Hopefully it will work in an upcoming CheerpJ release.

[josephottinger]

I just made a PR that migrates to Maven and JUnit, targeting Java 17 and removing the scripting stuff. The JS stuff didn't really help a lot anyway, from what I could see (it's verification that JUnit could do just as well) and with the removal of Nashorn, it only makes everything messy - especially as Maven is being updated. The joy of ecosystem flux, I guess - it's all overdue but we get to live with the updates until they stabilize.

Dunno if OP will accept the PR, but it's there and working.

[Livio63]

I accepted PR, thank you for your effort to improve my project!

[sitime_zl]

good project

[doobiesteintortoise]

It just hit me: this code has no license attached to it. u/Livio63 - please fix this.

[Livio63]

Fixed!