From cc19a6bee26032fa32e83d2435d33dac76bec58d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 17 Dec 2018 00:05:55 +0100
Subject: [PATCH 1/5] Add (guix json).

* guix/swh.scm: Use (guix json).
(define-json-reader, define-json-mapping): Move to...
* guix/json.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
---
 Makefile.am   |  1 +
 guix/json.scm | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 guix/json.scm

diff --git a/Makefile.am b/Makefile.am
index 1a3ca227a4..81f502d877 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -95,6 +95,7 @@ MODULES =					\
   guix/bzr-download.scm            		\
   guix/git-download.scm				\
   guix/hg-download.scm				\
+  guix/json.scm					\
   guix/swh.scm					\
   guix/monads.scm				\
   guix/monad-repl.scm				\
diff --git a/guix/json.scm b/guix/json.scm
new file mode 100644
index 0000000000..d446f6894e
--- /dev/null
+++ b/guix/json.scm
@@ -0,0 +1,63 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix json)
+  #:use-module (json)
+  #:use-module (srfi srfi-9)
+  #:export (define-json-mapping))
+
+;;; Commentary:
+;;;
+;;; This module provides tools to define mappings from JSON objects to SRFI-9
+;;; records.  This is useful when writing bindings to HTTP APIs.
+;;;
+;;; Code:
+
+(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
+following SPEC, a series of field specifications."
+  (define (json->record input)
+    (let ((table (cond ((port? input)
+                        (json->scm input))
+                       ((string? input)
+                        (json-string->scm input))
+                       ((hash-table? input)
+                        input))))
+      (let-syntax ((extract-field (syntax-rules ()
+                                    ((_ table (field key json->value))
+                                     (json->value (hash-ref table key)))
+                                    ((_ table (field key))
+                                     (hash-ref table key))
+                                    ((_ table (field))
+                                     (hash-ref table
+                                               (symbol->string 'field))))))
+        (ctor (extract-field table spec) ...)))))
+
+(define-syntax-rule (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."
+  (begin
+    (define-record-type rtd
+      (ctor field ...)
+      pred
+      (field getter) ...)
+
+    (define-json-reader json->record ctor
+      (field spec ...) ...)))
-- 
2.29.2