Re: Exception with multiple irritants

[Maxime Devos]

On 25-11-2022 01:03, Zelphir Kaltstahl wrote:
> ice-9/boot-9.scm:1685:16: In procedure raise-exception:
> ERROR:
>    1. &contract-violated
>    2. &message: "contract violated"
>    3. &origin: bla
>    4. &irritants: (> foo 10)
>    5. &irritants: (> 10 10)

I don't understand this -- (> 10 10) is always false, no?  I would 
interpret such an error message as 'you can't call this procedure at 
all, it requires a contradiction to hold'.  What's the purpose of (> 10 
10) here?  I guess 'foo=10'?

If you want to include the value of 'foo', this can be made more 
explicit, e.g.:

  4. &unsatisfied-constraint: (> foo 10)
  5. &argument: foo, 10  (i.e. this &argument condition has two fields)

That would avoid the vague '&irritants' -- I mean,

      A base type used for storing information about the causes of
     another condition in a compound condition.

is rather vague, it could refer to 'the condition causing this 
condition', or the values of the arguments, or some property of those 
arguments, or ...

> ~~~~
>
> Nice! Now I have the value of `foo` in this case as well and that could 
> be 
> useful information in cases, when I get a violated contract unexpectedly.
>
> However, having irritants twice seems a bit weird. Is this something, 
> that is safe to do? Something expected and probably unchanging in future 
> versions of GNU Guile? Or does it merely work by chance?
>
> I could always make another exception type like 
> "exception-with-irritant-values" 
> or something and use that, instead of a second "with irritants" call.

I don't know if having multiple instances of the same condition type 
inside a single condition is supported.

However, given that &irritants is plural (instead of a singular 
&irritant), and the documentation also mentions 'causes' (plural!):

     A base type used for storing information about the causes of
     another condition in a compound condition.

... why not make the value of &irritants a list, e.g.:

>    1. &contract-violated
>    2. &message: "contract violated"
>    3. &origin: bla
>    4. &irritants: ((> foo 10) (> 10 10))

Greetings,
Maxime.

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