job-specifier: Add '%find-best-next' procedure.

* scm/mcron/job-specifier.scm (find-best-next): Rename to ...
(%find-best-next): ... this.  Rewrite it using a functional style.
All callers changed.

2 files changed, 33 insertions, 42 deletions

diff --git a/scm/mcron/job-specifier.scm b/scm/mcron/job-specifier.scm
index 3f73b82..1c2f9d9 100644
--- a/scm/mcron/job-specifier.scm
+++ b/scm/mcron/job-specifier.scm
@@ -24,6 +24,13 @@
 ;; add-job function), and the procedure for declaring environment modifications.
 
 (define-module (mcron job-specifier)
+  #:use-module (ice-9 match)
+  #:use-module (mcron core)
+  #:use-module (mcron environment)
+  #:use-module (mcron vixie-time)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:re-export (append-environment-mods)
   #:export (range
             next-year-from         next-year
             next-month-from        next-month
@@ -33,15 +40,7 @@
             next-second-from       next-second
             set-configuration-user
             set-configuration-time
-            job
-            find-best-next)
-  #:use-module (mcron core)
-  #:use-module (mcron environment)
-  #:use-module (mcron vixie-time)
-  #:use-module (srfi srfi-1)
-  #:use-module (srfi srfi-26)
-  #:re-export (append-environment-mods))
-
+            job))
 
 (define* (range start end #:optional (step 1))
   "Produces a list of values from START up to (but not including) END.  An
@@ -49,25 +48,18 @@ optional STEP may be supplied, and (if positive) only every step'th value will
 go into the list.  For example, (range 1 6 2) returns '(1 3 5)."
   (unfold (cut >= <> end) identity (cute + <> (max step 1)) start))
 
-;; Internal function (not supposed to be used directly in configuration files;
-;; it is exported from the module for the convenience of other parts of the
-;; mcron implementation) which takes a value and a list of possible next values
-;; (all assumed less than 9999). It returns a pair consisting of the smallest
-;; element of the list, and the smallest element larger than the current
-;; value. If an example of the latter cannot be found, 9999 will be returned.
-
-(define (find-best-next current next-list)
-  (let ((current-best (cons 9999 9999)))
-    (for-each (lambda (allowed-time)
-                          (if (< allowed-time (car current-best))
-                              (set-car! current-best allowed-time))
-                          (if (and (> allowed-time current)
-                                   (< allowed-time (cdr current-best)))
-                              (set-cdr! current-best allowed-time)))
-              next-list)
-    current-best))
-
-
+(define (%find-best-next current next-list)
+  ;; Takes a value and a list of possible next values (all assumed less than
+  ;; 9999). It returns a pair consisting of the smallest element of the
+  ;; NEXT-LIST, and the smallest element larger than the CURRENT value. If an
+  ;; example of the latter cannot be found, 9999 will be returned.
+  (let loop ((smallest 9999) (closest+ 9999) (lst next-list))
+    (match lst
+      (() (cons smallest closest+))
+      ((time . rest)
+       (loop (min time smallest)
+             (if (> time current) (min time closest+) closest+)
+             rest)))))
 
 ;; Internal function to return the time corresponding to some near future
 ;; hour. If hour-list is not supplied, the time returned corresponds to the
@@ -89,7 +81,7 @@ go into the list.  For example, (range 1 6 2) returns '(1 3 5)."
                    set-component! set-higher-component!)
   (if (null? value-list)
       (set-component! time (+ (component time) 1))
-      (let ((best-next (find-best-next (component time) (car value-list))))
+      (let ((best-next (%find-best-next (component time) (car value-list))))
         (if (eqv? 9999 (cdr best-next))
             (begin
               (set-higher-component! time (+ (higher-component time) 1))
diff --git a/scm/mcron/vixie-time.scm b/scm/mcron/vixie-time.scm
index 2f26a6d..a91fa89 100644
--- a/scm/mcron/vixie-time.scm
+++ b/scm/mcron/vixie-time.scm
@@ -15,15 +15,13 @@
 ;;   You should have received a copy of the GNU General Public License along
 ;;   with GNU mcron.  If not, see <http://www.gnu.org/licenses/>.
 
-
 (define-module (mcron vixie-time)
-  #:export (parse-vixie-time)
-  #:use-module (mcron job-specifier))
-
-
-(use-modules (srfi srfi-1) (srfi srfi-13) (srfi srfi-14)
-             (ice-9 regex))
-
+  #:use-module (ice-9 regex)
+  #:use-module (mcron job-specifier)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-13)
+  #:use-module (srfi srfi-14)
+  #:export (parse-vixie-time))
 
 ;; In Vixie-style time specifications three-letter symbols are allowed to stand
 ;; for the numbers corresponding to months and days of the week. We deal with
@@ -179,11 +177,12 @@
 ;; simply unreadable without all of these aliases.
 
 (define (increment-time-component time time-spec)
-  (let* ((time-list   (time-spec:list   time-spec))
-         (getter      (time-spec:getter time-spec))
-         (setter      (time-spec:setter time-spec))
-         (next-best   (find-best-next (getter time) time-list))
-         (wrap-around (eqv? (cdr next-best) 9999)))
+  (let* ((time-list      (time-spec:list   time-spec))
+         (getter         (time-spec:getter time-spec))
+         (setter         (time-spec:setter time-spec))
+         (find-best-next (@@ (mcron job-specifier) %find-best-next))
+         (next-best      (find-best-next (getter time) time-list))
+         (wrap-around    (eqv? (cdr next-best) 9999)))
     (setter time ((if wrap-around car cdr) next-best))
     wrap-around))