[bug#30657] [PATCH 1/4] services: utils: Add 'push-tokens' and 'with-tokens-to-list'.

["Clément Lassieur" <clement@lassieur.org>]

* gnu/services/utils.scm: New file.
(push-tokens, with-tokens-to-list): New exported procedures.
(%tokens-stack): New parameter.
* gnu/local.mk: Add new file.
---
 gnu/local.mk           |  1 +
 gnu/services/utils.scm | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 gnu/services/utils.scm

diff --git a/gnu/local.mk b/gnu/local.mk
index 68f3a20f6..07cc2229a 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -482,6 +482,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/services/ssh.scm				\
   %D%/services/sysctl.scm			\
   %D%/services/telephony.scm			\
+  %D%/services/utils.scm			\
   %D%/services/version-control.scm              \
   %D%/services/vpn.scm				\
   %D%/services/web.scm				\
diff --git a/gnu/services/utils.scm b/gnu/services/utils.scm
new file mode 100644
index 000000000..a8d7981b2
--- /dev/null
+++ b/gnu/services/utils.scm
@@ -0,0 +1,41 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Clément Lassieur <clement@lassieur.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 (gnu services utils)
+  #:export (push-tokens
+            with-tokens-to-list))
+
+(define %tokens-stack (make-parameter #f))
+
+(define (push-tokens . tokens)
+  "Push TOKENS to %TOKENS-STACK so that they will be returned by
+WITH-TOKENS-TO-LIST."
+  (unless (%tokens-stack)
+    (error "not called within the dynamic extent of 'with-tokens-to-list'"))
+  (%tokens-stack (append (%tokens-stack) tokens)))
+
+(define (with-tokens-to-list thunk)
+  "Call THUNK and return the tokens that were pushed to %TOKENS-STACK as a
+list."
+  (parameterize ((%tokens-stack '()))
+    (thunk)
+    (%tokens-stack)))
+
+;;; Local Variables:
+;;; eval: (put 'with-tokens-to-list 'scheme-indent-function 0)
+;;; End:
-- 
2.16.2