Re: doubly quoted list in gnu-build

[Wojtek Kosior]

> hi,
> 
> why do the configure-flags and make-flags need to be doubly quote in the 
> gnu-build procedure?

Because later in that function they get unquoted inside a gexp using
`#$` (i.e. `ungexp`).

If you write a gexp like

> (let ((somelist '("a" "b" "c")))
>   #~(display #$somelist))

on the build side it will resolve to

> (display ("a" "b" "c"))

which will of course fail because `"a"` is not a proper function. You
instead want to get this

> (display '("a" "b" "c"))

which can be achieved by e.g. double-quoting the value that gets
ungexp'd, e.g. with

> (let ((somelist ''("a" "b" "c")))
>   #~(display #$somelist))

The following should also work for this list

> (let ((somelist '("a" "b" "c")))
>   #~(display '#$somelist))

In many places in Guix code a function `sexp->gexp` is also used
together with `'#$`. I suspect it does some extra stuff. I don't know
what exactly.

The relevant part where those double-quoted lists are used is

>                            #:locale #$locale
>                            #:bootstrap-scripts #$bootstrap-scripts
>                            #:configure-flags #$(if (pair? configure-flags)
>                                                    (sexp->gexp 
> configure-flags) ; here
>                                                    configure-flags)
>                            #:make-flags #$(if (pair? make-flags)
>                                               (sexp->gexp make-flags)         
>   ; here
>                                               make-flags)
>                            #:out-of-source? #$out-of-source?
>                            #:tests? #$tests?
>                            #:test-target #$test-target

When a double-quoted list is used, the "true" expression of each `if`
clause is used :)

Wojtek

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On Wed, 7 Dec 2022 00:14:51 -0600
jgart <jgart@dismail.de> wrote:

> hi,
> 
> why do the configure-flags and make-flags need to be doubly quote in the 
> gnu-build procedure?
> 
> (define* (gnu-build name inputs
>                     #:key
>                     guile source
>                     (outputs '("out"))
>                     (search-paths '())
>                     (bootstrap-scripts %bootstrap-scripts)
>                     (configure-flags ''()) ; here
>                     (make-flags ''()) ; here
>                     (out-of-source? #f)
>                     (tests? #t)
>                     (test-target "check")
>                     (parallel-build? #t)
>                     (parallel-tests? #t)
>                     (patch-shebangs? #t)
>                     (strip-binaries? #t)
>                     (strip-flags %strip-flags)
>                     (strip-directories %strip-directories)
>                     (validate-runpath? #t)
>                     (make-dynamic-linker-cache? #t)
>                     (license-file-regexp %license-file-regexp)
>                     (phases '%standard-phases)
>                     (locale "en_US.utf8")
>                     (system (%current-system))
>                     (build (nix-system->gnu-triplet system))
>                     (imported-modules %gnu-build-system-modules)
>                     (modules %default-modules)
>                     (substitutable? #t)
>                     allowed-references
>                     disallowed-references)
> 
>

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