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json: Re-export 'define-json-mapping' from (json) when available.

This prepares for the migration to Guile-JSON 4.3.0.

* guix/json.scm (define-as-needed): New macro.
(define-json-mapping): Use 'define-as-needed' instead of
Ludovic Courtès 1 year ago
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  1. 31


@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2018, 2019 Ludovic Courtès <>
;;; Copyright © 2018, 2019, 2020 Ludovic Courtès <>
;;; This file is part of GNU Guix.
@ -18,15 +18,33 @@
(define-module (guix json)
#:use-module (json)
#:use-module (srfi srfi-9)
#:export (define-json-mapping))
#:use-module (srfi srfi-9))
;;; Commentary:
;;; Helpers to map JSON objects to SRFI-9 records. Taken from (guix swh).
;;; This module is superseded by 'define-json-mapping' as found since version
;;; 4.2.0 of Guile-JSON and will be removed once migration is complete.
;;; Code:
(define-syntax define-as-needed
(lambda (s)
"Define the given syntax rule unless (json) already provides it."
(syntax-case s ()
((_ (macro args ...) body ...)
(if (module-defined? (resolve-interface '(json))
(syntax->datum #'macro))
#'(eval-when (expand load eval)
;; Re-export MACRO from (json).
(module-re-export! (current-module) '(macro)))
;; Using Guile-JSON < 4.2.0, so provide our own MACRO.
(define-syntax-rule (macro args ...)
body ...)
(eval-when (expand load eval)
(module-export! (current-module) '(macro)))))))))
(define-syntax-rule (define-json-reader json->record ctor spec ...)
"Define JSON->RECORD as a procedure that converts a JSON representation,
read from a port, string, or hash table, into a record created by CTOR and
@ -48,8 +66,11 @@ following SPEC, a series of field specifications."
(symbol->string 'field))))))
(ctor (extract-field table spec) ...)))))
(define-syntax-rule (define-json-mapping rtd ctor pred json->record
(field getter spec ...) ...)
;; For some reason we cannot just have colliding definitions of
;; 'define-json-mapping' (that leads to a build failure in users of this
;; module), hence the use of 'define-as-needed'.
(define-as-needed (define-json-mapping rtd ctor pred json->record
(field getter spec ...) ...)
"Define RTD as a record type with the given FIELDs and GETTERs, à la SRFI-9,
and define JSON->RECORD as a conversion from JSON to a record of this type."