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combinators: Add 'define-compile-time-procedure'.

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* guix/combinators.scm (procedure-call-location): New syntax parameter.
(define-compile-time-procedure): New macro.
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Ludovic Courtès 2021-12-18 17:54:23 +01:00
parent bdaf38a6e0
commit ddf9345dfe
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GPG key ID: 090B11993D9AEBB5
1 changed files with 48 additions and 2 deletions
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50
guix/combinators.scm
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@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2012-2017, 2021 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2014 Eric Bavier <bavier@member.fsf.org>
;;; Copyright © 2020 Arun Isaac <arunisaac@systemreboot.net>
;;;
@ -24,7 +24,9 @@ (define-module (guix combinators)
#:export (fold2
fold-tree
fold-tree-leaves
compile-time-value))
compile-time-value
procedure-call-location
define-compile-time-procedure))
;;; Commentary:
;;;
@ -100,4 +102,48 @@ (define-syntax compile-time-value ;not quite at home
(_ #`'#,(datum->syntax s val)))))))
v))))
(define-syntax-parameter procedure-call-location
(lambda (s)
(syntax-violation 'procedure-call-location
"'procedure-call-location' may only be used \
within 'define-compile-time-procedure'"
s)))
(define-syntax-rule (define-compile-time-procedure (proc (arg pred) ...)
body ...)
"Define PROC as a macro such that, if every actual argument in a \"call\"
matches PRED, then BODY is evaluated at macro-expansion time. BODY must
return a single value in a type that has read syntax--e.g., numbers, strings,
lists, etc.
BODY can refer to 'procedure-call-location', which is bound to a source
property alist corresponding to the call site.
This macro is meant to be used primarily for small procedures that validate or
process its arguments in a way that may be equally well performed at
macro-expansion time."
(define-syntax proc
(lambda (s)
(define loc
#`(identifier-syntax
'#,(datum->syntax #'s (syntax-source s))))
(syntax-case s ()
((_ arg ...)
(and (pred (syntax->datum #'arg)) ...)
(let ((arg (syntax->datum #'arg)) ...)
(syntax-parameterize ((procedure-call-location
(identifier-syntax (syntax-source s))))
body ...)))
((_ actual (... ...))
#`((lambda (arg ...)
(syntax-parameterize ((procedure-call-location #,loc))
body ...))
actual (... ...)))
(id
(identifier? #'id)
#`(lambda (arg ...)
(syntax-parameterize ((procedure-call-location #,loc))
body ...)))))))
;;; combinators.scm ends here