Re: [GSOC][PATCH] userdiff: add support for Scheme

[Atharva Raykar <raykar.ath@gmail.com>]

> On 29-Mar-2021, at 15:48, Phillip Wood <phillip.wood123@gmail.com> wrote:
> 
> Hi Atharva
> 
> On 28/03/2021 13:23, Atharva Raykar wrote:
>> On 28-Mar-2021, at 05:16, Johannes Sixt <j6t@kdbg.org> wrote:
> > [...]
>>>> diff --git a/t/t4018/scheme-local-define b/t/t4018/scheme-local-define
>>>> new file mode 100644
>>>> index 0000000000..90e75dcce8
>>>> --- /dev/null
>>>> +++ b/t/t4018/scheme-local-define
>>>> @@ -0,0 +1,4 @@
>>>> +(define (higher-order)
>>>> +  (define local-function RIGHT
>>> 
>>> ... this one, which is also indented and *is* marked as RIGHT.
>> In this test case, I was explicitly testing for an indented '(define'
>> whereas in the former, I was testing for the top-level '(define-syntax',
>> which happened to have an internal define (which will inevitably show up
>> in a lot of scheme code).
> 
> It would be nice to include indented define forms but including them means that any change to the body of a function is attributed to the last internal definition rather than the actual function. For example
> 
> (define (f arg)
>  (define (g x)
>    (+ 1 x))
> 
>  (some-func ...)
>  ;;any change here will have '(define (g x)' in the hunk header, not '(define (f arg)'

The reason I went for this over the top level forms, is because
I felt it was useful to see the nearest definition for internal
functions that often have a lot of the actual business logic of
the program (at least a lot of SICP seems to follow this pattern).
The disadvantage is as you said, it might also catch trivial inner
functions and the developer might lose context.

Another problem is it may match more trivial bindings, like:

(define (some-func things)
  ...
  (define items '(eggs
                  ham
                  peanut-butter))
  ...)

What I have noticed *anecdotally* is that this is not common enough
to be too much of a problem, and local define bindings seem to be more
favoured in Racket than other Schemes, that use 'let' more often.

> I don't think this can be avoided as we rely on regexs rather than parsing the source so it is probably best to only match toplevel defines.

The other issue with only matching top level defines is that a
lot of scheme programs are library definitions, something like

(library
    (foo bar)
  (export ...)
  (define ...)
  (define ...)
  ;; and a bunch of other definitions...
)

Only matching top level defines will completely ignore matching all
the definitions in these files.