Re: Outreachy - Guix Data Service: questions about improving the data for derivation comparisons.

[Luciana Lima Brito <lubrito@posteo.net>]

Hi,

On Thu, 22 Apr 2021 22:15:34 +0100
Christopher Baines <mail@cbaines.net> wrote:

I'm stuck.
 
> I'd suggest avoiding '() as the value for hash and hash-algorithm when
> they're NULL in the database. One option here that I've used in some
> places is to return a alist rather than a list. This can simplify JSON
> output since it's often a alist that's desired, and can avoid breaking
> matches when they're matching on the list.
> 
> Does that make sense?

It is not so clear to me. I tried three ways, always testing on
"outputs":

First, I tried using an alist  within
the map function on derivation-outputs-differences-data
(comparison.scm), and I applied a list->vector on the result. It
worked, but I do believe that this is not the way we want it to be.
This way the label comes as another field, and I got the result like
this:

code:

`((label . ,(cond
		((and (memq base-derivation-id
			parsed-derivation-ids)
              	      (memq target-derivation-id
			parsed-derivation-ids))
                   'common)
         	((memq base-derivation-id parsed-derivation-ids)
		   'base)
              	(else 'target)))
           (name . ,output-name)
           (path . ,path)
           ,@(if (string? hash-algorithm)
                 `((hash-algorithm . ,hash-algorithm))
                 '())
           ,@(if (string? hash)
                 `((hash . ,hash))
                 '())
           (recursive . ,(string=? recursive "t")))

json outputs:
   0:
	label: "base"
	name: "foo"
	path: "bar"
	recursive: #f

This way I only used the function derivation-outputs-differences-data,
not using group-to-alist or group-by-last-element.

The second way I tried was to pass an alist as first element of the list
and append the labels (base or/and target):

(list
         `((name . ,output-name)
           (path . ,path)
           ,(if (string? hash-algorithm)
               `(hash-algorithm . ,hash-algorithm)
               '())
           ,(if (string? hash)
               `(hash . ,hash)
               '())
           (recursive . ,(string=? recursive "t")))
         
         (append (if (memq base-derivation-id
                           parsed-derivation-ids)
                     '(base)
                     '())
                 (if (memq target-derivation-id
                           parsed-derivation-ids)
                     '(target)
                     '())))

But this seemed to result in an extra parenthesis in the result, which
didn't work.

So I tried a third way, using the pairs
individually in the list and the append.

(list
         `(name . ,output-name)
         `(path . ,path)
         (if (string? hash-algorithm)
                 `(hash-algorithm . ,hash-algorithm)
                 '())
         (if (string? hash)
                 `(hash . ,hash)
                 '())
         `(recursive . ,(string=? recursive "t"))
         
         (append (if (memq base-derivation-id
                           parsed-derivation-ids)
                     '(base)
                     '())
                 (if (memq target-derivation-id
                           parsed-derivation-ids)
                     '(target)
                     '())))


Furthermore, all these methods would require tweaking the html
processing.

Here is an idea I just had. The first way I tried returned a
vector. This worked but kind of ugly. As I am already
getting the alist, I just thought about writing another function to
group by the first elements (the labels), something like this:

(group-by-first-element l)

where l is the alist I get from the first method I mentioned.
And then, I would have the following alist:
((base (...))
 (target (...))
 (common ((...)(...)(...))))

which is the current alist we are using in controller.scm.
Problem is, I still don't know how to do this, and this seems somewhat
too long winded to get the proper alist.

-- 
Best Regards,

Luciana Lima Brito
MSc. in Computer Science