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Re: better error messages through assertions
From: |
Ludovic Courtès |
Subject: |
Re: better error messages through assertions |
Date: |
Wed, 30 Mar 2022 11:37:10 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Hi Philip,
Philip McGrath <philip@philipmcgrath.com> skribis:
> I'm thinking that a reasonable place to start might be to implement a
> `contract->sanitizer` form that would allow using contracts to create
> sanitizers, ideally with no changes to `(guix records)`.
OK. I’d prefer if people who define record types could directly write:
(field getter (contract integer/c))
rather than:
(field getter (sanitizer (contract->sanitizer integer/c)))
But that’s more of a detail.
> What is the preferred mechanism for exceptions?
For Guix code, SRFI-34/35.
> Likewise, what record system should I use?
SRFI-9.
(Perhaps we should put answers to these questions in the “Coding Style”
section of the manual.)
> Also, I don't know much about how the "abi" aspect of (guix records)
> works and what types of changes there would trigger rebuilds. (Though,
> again, I hope no changes would be needed for the proof-of-concept phase.)
I don’t think you need to worry about that.
> Another problem here seems to be the fault of (srfi srfi-9). For example:
[...]
> scheme@(guile-user)> (container-contents '())
> ice-9/boot-9.scm:1685:16: In procedure raise-exception:
> In procedure struct-vtable: Wrong type argument in position 1
> (expecting struct): ()
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> In current input:
> 3:0 1 (_)
> In ice-9/boot-9.scm:
> 1685:16 0 (raise-exception _ #:continuable? _)
> ```
>
> It seems like `container-contents` and other field accessors ought to
> check their arguments with `container?` (or the applicable predicate)
> and not leave error reporting to `struct-vtable`.
SRFI-9 generates the smallest amount of code for the job:
--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(srfi srfi-9)
scheme@(guile-user)> (define-record-type <foo>
(make-foo x)
foo?
(x foo-x))
scheme@(guile-user)> ,optimize (foo-x '())
$9 = (if (eq? (struct-vtable '()) <foo>)
(struct-ref '() 0)
(throw 'wrong-type-arg
'foo-x
"Wrong type argument: ~S"
(list '())
(list '())))
--8<---------------cut here---------------end--------------->8---
With Guile 3, it might be that adding an extra ‘struct?’ test would have
little effect on performance; we’d need to check.
> Perhaps this could be fixed in the (guix records) layer?
Could be, yes.
Thanks for looking into this!
Ludo’.