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Re: [PATCH 3/7] import cran: description->package: Also return package d
From: |
Ricardo Wurmus |
Subject: |
Re: [PATCH 3/7] import cran: description->package: Also return package dependencies. |
Date: |
Wed, 31 Aug 2016 12:39:33 +0200 |
User-agent: |
mu4e 0.9.16; emacs 24.5.1 |
Ludovic Courtès <address@hidden> writes:
> Ricardo Wurmus <address@hidden> skribis:
>
>> Ricardo Wurmus <address@hidden> writes:
>>
>>> Ludovic Courtès <address@hidden> writes:
>>>
>>>> Ricardo Wurmus <address@hidden> skribis:
>>>>
>>>>> * guix/import/cran.scm (description->package): Return package
>>>>> dependencies in addition to generated package expression.
>>>>
>>>> What would you think of making it return a SRFI-41 stream of packages
>>>> instead? Or maybe two values: the package asked for, and the stream
>>>> containing its dependencies. That would hide the package lookup
>>>> machinery.
>>>
>>> That’s a very good idea! I’ll play around with this and submit a new
>>> patch.
>>
>> I’ve been playing with this for a while and although it looks prettier
>> to a user it has some disadvantages to use streams here. The first is
>> that it becomes more difficult to avoid duplicate work. The second is
>> that we can no longer easily generate an order of package expressions
>> from leaf nodes to the root.
>>
>> Consider this case where “plotly” should be imported. The new inputs
>> look like this:
>>
>> plotly : (ggplot2 digest)
>> ggplot2 : (digest mass)
>> digest : ()
>> mass : ()
>>
>> The generated stream may look like this:
>>
>> (plotly ggplot2 digest mass digest)
>>
>> This happens because we only know about the next set of inputs upon
>> evaluation of the stream elements. Of course there are ways to fix
>> this, but they involve extending or wrapping “cran->guix-package” to
>> make sure that we keep track of top-level dependencies as we traverse
>> the list of dependencies recursively.
>>
>> Maybe I’m doing this wrong?
>>
>>
>> I rewrote description->package to essentially do this:
>>
>> (stream-cons the-package-expression
>> (stream-concat
>> (let ((unpackaged (unpackaged-dependencies
>> propagate guix-name)))
>> (stream-map (cran->guix-package name repository)
>> (list->stream unpackaged)))))
>>
>> I.e. the first element of the stream is the imported package expression;
>> the tail is a concatenation of streams of packages with their
>> dependencies just like this one. Here’s the stream before
>> concatenation:
>>
>> (plotly (ggplot2 (digest ()) (mass ()))
>> (digest ()))
>>
>> To render this in the correct order we’d have to turn this tree inside
>> out. Maybe this isn’t so well-suited to a representation as a stream
>> after all. To turn it inside out we have to evaluate the whole tree
>> anyway.
>>
>> What do you think? Is it worth expressing this as a stream? If so, do
>> you have any recommendations on how to approach this?
>>
>> Or would it be okay to let “description->package” return two values: a
>> package expression and a list of unpackaged package names, which can
>> then be processed by a separate procedure? (That’s what I submitted
>> earlier.)
>
> I think you should go ahead with what you proposed if the other option
> sounds like a headache. Sorry for blocking you for this long!
No problem. I would really like to use streams, so it’s worth the
wait. Can’t avoid the headache :)
> In theory it would be possible to do something like:
>
> (define (description->package repo meta)
> (stream-cons `(package …)
> (stream-unfold (lambda (state)
> (description->package
> repo
> (first-dependency state)))
> (lambda (state)
> (done? state))
> (lambda (state)
> (next-dependency state))
> (make-state propagate (setq)))))
>
> … where the state is roughly a pair containing the list of next
> dependencies and the set of already visited dependencies (to avoid
> duplicates).
That’s a good hint. “stream-unfold” makes my head spin, to be honest.
> But again, this is probably easier said than done, so no problem with
> keeping the initial option.
I’ll read the documentation for “stream-unfold” again and try once more.
If I really cannot make it I’ll go ahead with the initial
implementation and submit a new patch set.
~~ Ricardo