Subject: [bug#51655] [PATCH] build-system: haskell: Add ‘package-with-explicit-haskell’ procedure.

From: zimoun <[email-masked]>
Date: Mon, 15 Nov 2021 16:03:50 +0100

Hi,

On Sun, 07 Nov 2021 at 11:55, Xinglu Chen <[email-masked]> wrote:
> * guix/packages.scm (package-with-explicit-compiler): New procedure;
> factorized from ‘package-with-explicit-python’.
> * guix/build-system/python.scm (package-with-explicit-python): Use
> ‘package-with-explicit-compiler’.
> * guix/build-system/haskell.scm (package-with-explicit-haskell): New procedure.
> * doc/guix.texi (Defining Package Variants): Document it.
> ---
>  doc/guix.texi                 | 37 ++++++++++++++++++
>  guix/build-system/haskell.scm |  8 ++++
>  guix/build-system/python.scm  | 71 +++++++----------------------------
>  guix/packages.scm             | 55 +++++++++++++++++++++++++++
>  4 files changed, 113 insertions(+), 58 deletions(-)

Neat refactoring! :-)  It is something discussing several times and I do
not know if ’package-with-explicit-ocaml’ could not be added too.  The
issue is that it depends on more than only one element for “compiling”:
ocaml, findlib and dune.

On the other hand, guix/build-system/gnu.scm contains
’package-with-explicit-inputs*’ which is more or less the same idea.
And ’transform-package-toolchain’ is another instance.  This
’package-with-explicit-{ocaml,python}’ pre-dates the transformations and
deep rewriting.

Therefore, maybe refactor could revisit the complete story.

Well, I had headaches last time I gave a look at transformations.  And I
do not know if it is possible to have a generic transformation for
rewriting implicit inputs of all build systems.  That’s something that
could be nice to nice: ’package-with-explicit-python’ based on a
“generic” ’package-with-explicit-compiler’ (compiler or toolchain
though) and provides ’package-with-explicit-*’ for all build systems
(ocaml, ghc, emacs, guile, etc.).

> +@lisp
> +(use-modules (guix build-system haskell))
> +
> +(define (default-haskell-8.8)
> +  ;; Lazily resolve the binding to avoid a circular dependency.
> +  (let ((haskell (resolve-interface '(gnu packages haskell))))
> +    (module-ref haskell 'ghc-8.8)))
> +
> +(define package-with-haskell-8.8
> +  (package-with-explicit-haskell (delay (default-haskell-8.8))
> +                                 "ghc-" "ghc-8.8-"
> +                                 #:variant-property 'ghc-8.8-variant))
> +@end lisp

As Lars said, an instance is missing, IMHO.

Cheers,
simon