Hi everyone,
I thought it'd be fun to write a mathematical expression evaluator, a la Graham
Cox's GCMathParser, but one that was extensible. So I dusted off my parsing
skills and wrote DDMathParser: https://github.com/davedelong/DDMathParser
It's an NSString => NSNumber expression evaluator, and its major feature is
that you can define custom mathematical functions. So if you really need to
have a multiplyBy42() function, then you can quickly write one, register it,
and use it.
You can use it very simply:
NSLog(@"%@", [@"1 + 2" numberByEvaluatingString]); //logs "3"
Or very complexly:
DDMathParser * parser = [DDMathParser mathParserWithString:@"2 ** 3 **
2"];
[parser setPowerAssociativity:DDMathParserAssociativityRight];
DDExpression * e = [parser parsedExpression];
NSLog(@"%@", [e evaluateWithSubstitutions:nil evaluator:nil]); //logs
"512"
It supports pretty much all of the functions defined by NSExpression, plus many
more (primarily trig functions: sin(), cos(), atanh(), etc). And like I
mentioned above, you can create new functions as well.
It supports variables of the same format used by NSPredicate/NSExpression
("$variable") for substituting in values during evaluation.
It has rudimentary support for simplifying expressions, and I'm currently
working on support for translating an arbitrary "DDExpression" into an
NSExpression and still having it work properly (even with custom functions).
The source code is available on my github page, and I'd appreciate any comments
or feedback you might have.
https://github.com/davedelong/DDMathParser
Cheers,
Dave DeLong
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