From: Johannes Sixt <j6t@kdbg.org>
Date: Tue, 08 Mar 2022 18:32:15 GMT
Subject: Re: [PATCH v5] userdiff: add builtin diff driver for kotlin language.
Message-ID: <72aca675-4c65-36bf-1337-34b2d1f40bb4@kdbg.org>
In-Reply-To: <cf8a9316-c81e-2477-a565-1c38a168fc67@gmail.com>

Am 08.03.22 um 17:54 schrieb jaydeepjd.8914@gmail.com:
> So, the final regexes are these, right?:

Not quite.

> 
>      "[a-zA-Z_][a-zA-Z0-9_]*"
>      /* hexadecimal and binary numbers */
>      "|0[xXbB][0-9a-fA-F_]+[lLuU]*"
>      /* integers and floats */
>      "|[0-9][.]?[0-9_]+([Ee][-+]?[0-9]+)?[fFlLuU]*"

This would not match 12.5 because you allow only a single digit before
the decimal point. Perhaps

	"|[0-9][.0-9_]*([Ee][-+]?[0-9]+)?[fFlLuU]*"

>      /* floating point numbers beginning with decimal point */
>      "|[.][0-9][0-9_]*([Ee][-+]?[0-9]+)?[fFlL]?"
>      /* unary and binary operators */
>     
> "|[-+*/<>%&^|=!]?==?|--|\\+\\+|<<=|>>=|&&|[||]|->|\\.\\*|!!|::|[?:.][.:]"),

[||] does not work as you intend. A new suggestion: do not start with an
initial optional character in order to reduce the number of
backtrackings that the regular expression evaluation has to do. I would
write this line as

	"|[-+*/<>%&^|=!]==?|--|\\+\\+|<<=|>>=|&&|\\|\\||->|\\.\\*|!!|::|[?:.][.:]"),

BTW which operators are handled by "[?:.][.:]"? I'm asking because you
list :: separatly that would also be matched by this sub-expression.

-- Hannes