# regular expression for a formula

med yousfi

Greenhorn

Posts: 2

Matthew Brown

Bartender

Posts: 4568

9

posted 4 years ago

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?

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

posted 4 years ago

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

Ulf Dittmer

Rancher

Posts: 42970

73

posted 4 years ago

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.

posted 4 years ago

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.

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.