I've created a regular expression which allows users to make formulas in my application. The regular expression I have works fine, however I want users to make opening and closing parenthesis.
My current regular expression is:
(
^[(N|R)]: //START WITH N: OR R:
(?:
(?:
[-.0-9]+|BT|PT|PN|PR //ALLOW 48.934, BT, PT, PN OR PR
)
(?:
\+|\*|\-|\/ //ALLOW OPERATORS /,*,+ and -
)
)+ //REPEAT x TIMES
(?:
[-.0-9]+|BT|PT|PN|PR //MUST END WITH 48.934, BT, PT, PN OR PR
)
(?:
:V //ADD MANDATORY :V
)
(?:
[-.0-9]+ //CLOSE REGEX WITH NUMBER
)
)
A few examples in which the regular expression currently works:
N:0.3*BT/PN*PR:V1
N:2000+PN/BT:V0.5
R:BT*PN-500:V2
I'd like the regular expression to work with () which it currently doesn't for a few examples:
N:(2000+PN)/BT:V0.5
R:BT*(PN-500):V2
I've read about positive and negative lookahead, to create if / else structures but I can't seem to find the right logic for my needs.
Much appreciated if someone can guide me in the right direction.
P.S. I'm using the JavaScript regex engine.
Here is a modified version of your regex that allows for any number of matched (but not nested) parens (see on regex101):
(?=
[^()]*
(\([^()]+\)[^()]*)*
$
)
^[NR]: //START WITH N: OR R:
(?:
\(?(?:[-.0-9]+|BT|PT|PN|PR)\)? //ALLOW 48.934, BT, PT, PN OR PR
[-+*\/] //ALLOW OPERATORS /,*,+ and -
\(?(?:[-.0-9]+|BT|PT|PN|PR)\)? //ALLOW 48.934, BT, PT, PN OR PR
)+ //REPEAT x TIMES
(?:
[-+*\/] //ALLOW OPERATORS /,*,+ and -
(?:[-.0-9]+|BT|PT|PN|PR) //ALLOW 48.934, BT, PT, PN OR PR
\)?
)*`
:V //ADD MANDATORY :V
[-.0-9]+ //CLOSE REGEX WITH NUMBER
Explanation:
Other than some clean-up of [(N|R)] and other extraneous groupings, the main change is to add a positive lookahead at the very beginning to ensure that any parens are found in pairs:
(?=
[^()]*
(\([^()]+\)[^()]*)*
$
)
Then parens are allowed around each number or variable.