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# regular expression for a formula

med yousfi
Greenhorn
Posts: 2
Hello,i have an expression like this :SUM(10,20,ABS(-5)) it is a formula like a formula used in Excel .it is possible to match this expression using regular expression ??? the purpose is to validate an expression and generate an object from this expression.thanks

Matthew Brown
Bartender
Posts: 4568
9
Hi Med. Welcome to the Ranch!

It's probably possible. But it isn't enough to just give an example. I can give a regular expression that trivially matches that particular example and nothing else. You need to be able to describe the rules that apply. What are the allowed expressions, and how can we identify something that *doesn't* match?

med yousfi
Greenhorn
Posts: 2
the regular expression must be generic and accept the fact that a parameter of a function can be a function for exemple Sum(a1,Average(a2,a3,abs(a4))) a complex expression in this case Average(a2,a3,abs(a4)) is a parameter of Sum and abs(a4) is a parameter of the the function Average...

Joanne Neal
Rancher
Posts: 3742
16
Again you've just given an example. You need to define the rules. Personally I would look at using a lexical parser rather than regular expressions.

Ulf Dittmer
Rancher
Posts: 42972
73
Regular expressions are not powerful enough to match mathematical expressions of arbitrary depth. Look into parser generators like SableCC, JavaCC and Antlr; they probably have predefined grammars for mathematical expressions. Or use a lexer like JFlex; I've yet to come across something so complicated that I felt like I *needed* a parser generator; JFlex was always sufficient for my purposes. Your mileage, of course, may vary.

fred rosenberger
lowercase baba
Bartender
Posts: 12527
48
med yousfi wrote:the regular expression must be generic and accept the fact that a parameter of a function can be a function for exemple Sum(a1,Average(a2,a3,abs(a4))) a complex expression in this case Average(a2,a3,abs(a4)) is a parameter of Sum and abs(a4) is a parameter of the the function Average...

All of the examples you have given can be matched with

.*

That matches zero or more characters. But it probably isn't what you want.

I think you are putting the cart before the horse. You have decided to use regexes, and are asking how to force them to do what you want. That's like saying "I have a hammer - how do I use it to drill a 1/4" hole in a wall?"

sure, you MIGHT be able to do it if you really work at it, but it is not the right tool.

Instead, you should look at what you are trying to do, and then figure out what the right tool to do that is.

 Did you see how Paul cut 87% off of his electric heat bill with 82 watts of micro heaters?