From: Phillip Wood Date: Mon, 29 Mar 2021 10:12:33 GMT Subject: Re: [GSOC][PATCH] userdiff: add support for Scheme Message-ID: In-Reply-To: Hi Atharva On 28/03/2021 12:51, Atharva Raykar wrote: > On 28-Mar-2021, at 04:20, Junio C Hamano wrote: >> >> Atharva Raykar writes: >> >>> + /* >>> + * Scheme allows symbol names to have any character, >>> + * as long as it is not a form of a parenthesis. >>> + * The spaces must be escaped. >>> + */ >>> + "(\\.|[^][)(\\}\\{ ])+"), >> >> One or more "dot or anything other than SP or parentheses"? But >> a dot "." is neither a space or any {bra-ce} letter, so would the >> above be equivalent to >> >> "[^][()\\{\\} \t]+" >> >> I wonder... > > A backslash is allowed in scheme identifiers, and I erroneously thought that > the first part handles the case for identifiers such as `component\new` or > `\"id-with-quotes\"`. (I tested it with a regex engine that behaves differently > than the one git is using, my bad.) > >> I am also trying to figure out what you wanted to achieve by >> mentioning "The spaces must be escaped.". Did you mean something >> like (string->symbol "a symbol with SP in it") is a symbol? Even >> so, I cannot quite guess the significance of that fact wrt the >> regexp you added here? > > I initially tried using identifiers like `space\ separated` and they > seemed to work in my REPL, but turns out space separated identifiers in > scheme do not work with backslashes, and it was working because of the way > my terminal handled escaping. Space separated identifiers are declared like > `|space separated|` and this too only seems to work with Racket, not > the other Scheme implementations. I think the bar notation works with some other such as gambit and possibly guile (it's a while since I used the latter) Best wishes Phillip So I stand corrected here, and it's better > to drop this feature altogether. > > But somehow, the regexp you suggested, ie: > > "[^][()\\{\\} \t]+" > > does not handle the case of make\foo -> make\bar (it will only diff on foo). > I am not too sure why it treats backslashes as delimiters. > > This seems to actually do what I was going for: > > "(\\\\|[^][)(\\}\\{ ])+" > >> As we are trying to catch program identifiers (symbols in scheme) >> and numeric literals, treating any group of non-whitespace letters >> that is delimited by one or more whitespaces as a "word" would be a >> good first-order approximation, but in addition, as can be seen in >> an example like (a(b(c))), parentheses can also serve as such "word >> delimiters" in addition to whitespaces. So the regexp given above >> makes sense to me from that angle, especially if you do not limit >> the whitespace to only SP, but include HT (\t) as well. But was >> that how you came up with the regexp? > > Yes, this is exactly what I was trying to express. All words should be > delimited by either whitespace or a parenthesis, and all other special > characters should be accepted as part of the word. >