Re: [GSoC][PATCH v2 1/1] userdiff: add support for scheme

> Add a diff driver for Scheme-like languages which recognizes top level
> and local `define` forms, whether it is a function definition, binding,
> syntax definition or a user-defined `define-xyzzy` form.
> 
> Also supports R6RS `library` forms, `module` forms along with class and
> struct declarations used in Racket (PLT Scheme).
> 
> Alternate "def" syntax such as those in Gerbil Scheme are also
> supported, like defstruct, defsyntax and so on.
> 
> The rationale for picking `define` forms for the hunk headers is because
> it is usually the only significant form for defining the structure of
> the program, and it is a common pattern for schemers to have local
> function definitions to hide their visibility, so it is not only the top
> level `define`'s that are of interest. Schemers also extend the language
> with macros to provide their own define forms (for example, something
> like a `define-test-suite`) which is also captured in the hunk header.
> 
> Since it is common practice to extend syntax with variants of a form
> like `module+`, `class*` etc, those have been supported as well.
> 
> The word regex is a best-effort attempt to conform to R6RS[1] valid
> identifiers, symbols and numbers.
> 
> [1] http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-7.html#node_chap_4
> 
> Signed-off-by: Atharva Raykar <raykar.ath@gmail.com>
>[...]
> diff --git a/userdiff.c b/userdiff.c
> index 3f81a2261c..ac1999bbc5 100644
> --- a/userdiff.c
> +++ b/userdiff.c
> @@ -191,6 +191,10 @@ PATTERNS("rust",
>   	 "[a-zA-Z_][a-zA-Z0-9_]*"
>   	 "|[0-9][0-9_a-fA-Fiosuxz]*(\\.([0-9]*[eE][+-]?)?[0-9_fF]*)?"
>   	 "|[-+*\\/<>%&^|=!:]=|<<=?|>>=?|&&|\\|\\||->|=>|\\.{2}=|\\.{3}|::"),
> +PATTERNS("scheme",
> +	 "^[\t ]*(\\(((define|def(struct|syntax|class|method|rules|record|proto|alias)?)[-*/ \t]|(library|module|struct|class)[*+ \t]).*)$",
> +	 /* All words should be delimited by spaces or parentheses */
> +	 "([^][)(}{[ \t])+"),