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Re: Brainstorming ideas for define-configuration

From: jbranso
Subject: Re: Brainstorming ideas for define-configuration
Date: Fri, 10 Mar 2023 20:15:52 +0000

March 9, 2023 3:25 PM, "Liliana Marie Prikler" <> 

> Hi,
> Am Donnerstag, dem 09.03.2023 um 02:28 +0000 schrieb Bruno Victal:
> I smell bad code ahead.
>> We could provide procedures that validate each record type within
>> define-configuration itself instead of validating the value at
>> runtime (i.e. within the body of the service-type).
>> --8<---------------cut here---------------start------------->8---
>> ;; the common case
>> (define-configuration foo-configuration
>> (name
>> string
>> "Lorem ipsum...")
>> ;; ...
>> (validator procname))
>> ;; [bonus] Simpler configurations that only care for mutually-
>> exclusive fields
>> (define-configuration foo-configuration
>> (name
>> string
>> "Lorem ipsum...")
>> (title
>> string
>> "Lorem ipsum..."
>> (conflicts 'name)))
>> --8<---------------cut here---------------end--------------->8---
> Instead of providing both a name field and a title field, you might
> provide a field that can either be a name or a title or allow an even
> more powerful value type as long as it makes sense.

While I would agree that a guix service writer should avoid mutually
exclusive fieldnames and instead prefer mutually exclusive records
(and 95% of that time that will work), but may we examine it from a
user's perspective? How does the service writer differentiate from
a string title or string name?

Suppose that you want to respond to a king's rudeness. You can
secretly insult him or obviously insult him:

===Mutually exclusive records===, which are better from a maintainer's
perspective, but perhaps cause the user to write more scheme:

"..your traitor brother. Maybe I’ll feed him to wolves after I’ve
caught him. Did I tell you, I intend to challenge him to single

      (secret-insult “I should like to see that, Your Grace.”))))


"You can't insult me."

      (obvious-insult "We've had vicious kings and we've had idiot kings,
but I don't know if we've ever been cursed with a vicious idiot for
a king!"))))

===Mutually exclusive fieldnames===

"I am the KING!"

  (secret-insult "Any man who must say, 'I am the king' is no
true king. I'll show you that after I've won your war.")))


"You are Kingsguard!"

  (obvious-insult "...F*ck the King."))))

These examples are pretty wonky I will admit, but I really like
an option of having mutually exclusive fieldnames.  Having said all of this,
I will agree that that mutually exclusive fieldnames are a bit like "goto"
in C.  You really should never use them, unless you absolutely have to.



P.S.  I thought about not sending this email, then realized that someone
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