From: Chris Marusich <cmmarusich@gmail.com>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: guix-devel@gnu.org
Subject: Re: Mysterious error while refactoring guix/scripts/system.scm
Date: Sat, 24 Sep 2016 12:54:19 -0700 [thread overview]
Message-ID: <87zimxdqfo.fsf@gmail.com> (raw)
In-Reply-To: <87k2ezzi5c.fsf@gnu.org> ("Ludovic \=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\= \=\?utf-8\?Q\?s\?\= message of "Mon, 29 Aug 2016 17:53:03 +0200")
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Hi Ludo’,
Thank you for getting back to me!
ludo@gnu.org (Ludovic Courtès) writes:
> Hi Chris, and sorry for the delay!
>
> Chris Marusich <cmmarusich@gmail.com> skribis:
>
>> Backtrace:
>> In ice-9/boot-9.scm:
>> 157: 15 [catch #t #<catch-closure 26304a0> ...]
>> In unknown file:
>> ?: 14 [apply-smob/1 #<catch-closure 26304a0>]
>> In ice-9/boot-9.scm:
>> 63: 13 [call-with-prompt prompt0 ...]
>> In ice-9/eval.scm:
>> 432: 12 [eval # #]
>> In ice-9/boot-9.scm:
>> 2401: 11 [save-module-excursion #<procedure 264f940 at ice-9/boot-9.scm:4045:3 ()>]
>> 4050: 10 [#<procedure 264f940 at ice-9/boot-9.scm:4045:3 ()>]
>> 1724: 9 [%start-stack load-stack ...]
>> 1729: 8 [#<procedure 2668ea0 ()>]
>> In unknown file:
>> ?: 7 [primitive-load "/root/guix/scripts/guix"]
>> In guix/ui.scm:
>> 1209: 6 [run-guix-command system "list-generations"]
>> In ice-9/boot-9.scm:
>> 157: 5 [catch srfi-34 #<procedure 52af180 at guix/ui.scm:425:2 ()> ...]
>> 157: 4 [catch system-error ...]
>> In guix/scripts/system.scm:
>> 884: 3 [#<procedure 52ae750 at guix/scripts/system.scm:876:2 ()>]
>> 818: 2 [process-command list-generations () ...]
>> In guix/store.scm:
>> 1182: 1 [run-with-store # ...]
>> In unknown file:
>> ?: 0 [#<unspecified> #<build-daemon 256.15 52b8e80>]
>>
>> ERROR: In procedure #<unspecified>:
>> ERROR: Wrong type to apply: #<unspecified>
>
> This means that we’re trying to invoke #<unspecified>, but
> #<unspecified> is not a procedure.
>
> Note that this is from within ‘run-to-store’, which is the procedure to
> “run” a monadic value. So in effect, what happened is equivalent to:
>
>
> scheme@(guile-user)> ,use(guix monads)
> scheme@(guile-user)> ,use(guix store)
> scheme@(guile-user)> (with-store s
> (run-with-store s *unspecified*))
> ERROR: In procedure #<unspecified>:
> ERROR: Wrong type to apply: #<unspecified>
>
>
> The bug here is in fact a type error: ‘run-with-store’ expect a monadic
> value, but what we have here is a regular value.
>
> To “fix” it, we need:
>
>
> scheme@(guile-user)> (with-store s
> (run-with-store s
> (with-monad %store-monad (return *unspecified*))))
>
>
> … where ‘return’ procedure a monadic value from a normal value.
>
> In your case, ‘list-generations’ is not a monadic procedure (a procedure
> that returns a monadic value), so in this patch:
>
> (run-with-store store
> …
> (list-generations))
>
> … triggers this very type error.
I see. I've read the sections in the manual about gexps, and I've
peeked at the gexp code. I thought that basically I could use
run-with-store to run any Guile code I want, but I seem to be missing
something. I will try experimenting with monads and the store to learn
more and hopefully avoid surprises like this going forward.
> I imagine this may be more than you wanted to learn. ;-)
> Monads in a dynamically typed setting are kinda annoying because of
> this.
I appreciate the info. Hopefully I will fully understand it soon.
>> (define (process-command command args opts)
>> "Process COMMAND, one of the 'guix system' sub-commands. ARGS is its
>> argument list and OPTS is the option alist."
>> - (case command
>> - ((list-generations)
>> - ;; List generations. No need to connect to the daemon, etc.
>> - (let ((pattern (match args
>> - (() "")
>> - ((pattern) pattern)
>> - (x (leave (_ "wrong number of arguments~%"))))))
>> - (list-generations pattern)))
>> - (else
>> - (process-action command args opts))))
>> + (with-store store
>> + (set-build-options-from-command-line store opts)
>> +
>> + (run-with-store store
>> + (mbegin %store-monad
>> + (set-guile-for-build (default-guile))
>> + (case command
>> + ((list-generations)
>> + (let ((pattern (match args
>> + (() "")
>> + ((pattern) pattern)
>> + (x (leave (_ "wrong number of arguments~%"))))))
>> + (list-generations pattern)))
>> + (else
>> + (process-action command args opts))))
>> + #:system (assoc-ref opts 'system))))
>
> As the comment above suggests, the idea here was to avoid connecting to
> the daemon for operations that do not need it, such as
> ‘list-generations’. I think we should preserve this property.
The reason I wanted to perform this refactoring in the first place is
because I'd like to add a new procedure to guix/scripts/system.scm
called 'switch-to-system-generation'. Because this new procedure calls
other procedures which seem to require access to the store, I thought I
would need to call 'switch-to-system-generation' via 'run-with-store'.
Am I just confused?
In particular, 'switch-to-system-generation' will eventually call the
existing procedure 'grub-configuration-file' (defined in
gnu/system/grub.scm). As I understand it, 'grub-configuration-file'
returns a derivation that builds a GRUB configuration file. This
existing 'grub-configuration-file' procedure does a lot with the store
and gexps. I thought that if I didn't use 'run-with-store' to run
'switch-to-system-generation', it wouldn't work because
'grub-configuration-file' wouldn't work.
> Thanks for your work! I’m sorry this is more painful than I thought.
> :-/
>
> Ludo’.
I'm happy to help. I just wish I understood these monads better. And I
wish I had more time to work on it! Anyway, I'll keep at it.
--
Chris
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next prev parent reply other threads:[~2016-09-24 19:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-04 6:20 Mysterious error while refactoring guix/scripts/system.scm Chris Marusich
2016-08-04 7:56 ` Andy Wingo
2016-08-10 7:23 ` Chris Marusich
2016-08-29 15:53 ` Ludovic Courtès
2016-09-24 19:54 ` Chris Marusich [this message]
2016-09-30 20:36 ` Ludovic Courtès
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