Re: Guix records

[Taylan Kammer <taylan.kammer@gmail.com>]

On 05.02.2021 17:51, Olivier Dion via General Guile related discussions 
wrote:
> Hello,
> 
> In the module (guix records), there's some very nice syntax rule
> `define-record-type*` that allows very powerfull declarative style of
> records.  For example:
> ----------------------------------------------------------------------
> (employee
>    (age  30)
>    (name "Foo")
>    (profession "Teacher"))
> ----------------------------------------------------------------------
> 
> I would like to use this feature in my software.  However, I don't want
> to have Guix as a dependency only for that.  For now, I've copied the
> content of (guix records) into (my-software records).  But this put
> burden of maitenance into my hands.
> 
> Thus, I'm looking for an alternative, perhaps there's a Guile library
> (other than Guix' module) or a SRFI that offers similar feature?
> 

The most feature-rich record system supported by Guile is probably the 
R6RS record system, which is available through the modules:

   (rnrs records syntactic (6))
   (rnrs records procedural (6))
   (rnrs records inspection (6))

However, it doesn't allow a definition style like in your example, where 
you explicitly name the fields that you're assigning values to during 
instance creation.

It does, however, implicitly define getters (and setters for mutable 
fields).

The Guile documentation is brief.  You might want to read the R6RS spec 
or search for another guide for detailed explanations and examples of 
how to use the R6RS record system, if it sounds interesting.

Note that it's quite dissimilar to the SRFI-9 system, and some aspects 
of it are rather complex, which is why many people don't like it.  To be 
honest I find some of those complex features quite ingenious on paper, 
though I couldn't say how often they would prove to be useful in practice.

Here's a super brief example usage of R6RS records, demonstrating that 
field accessors are defined implicitly, but constructors still use an 
unnamed sequence of arguments to assign fields:

   (import (rnrs records syntactic (6)))  ; must use 'import' for R6RS

   (define-record-type (cat make-cat cat?) (fields name age color))

   (define garfield (make-cat "Garfield" 42 'orange))

   (cat-color garfield)  ;=>  orange



Then there is SRFI-99 which could be seen as an update to SRFI-9, but 
last I checked it's not in Guile yet.  It also doesn't really feature 
the declarative style like in your example.



- Taylan