mu-scm: add string->time and time->string

Replace the iso-date->time-t and v.v. functions with something more
customizable. Add more tests.

Use some (internal for now) %preferences variable for the defaults. TBD... maybe
should become a fluid?

scm/mu-scm-test.scm

@@ -49,7 +49,8 @@
   (let ((msg (car (mfind "" #:sort-field 'date #:reverse? #t))))
 
     (test-equal "test with multi to and cc" (subject msg) )
-    (test-equal "2016-05-15T16:57:25" (time-t->iso-date (date msg))))
+    (test-equal "2016-05-15 16:57:25"
+      (time->string (date msg) #:format "%F %T" #:utc? #t)))
 
   (test-end "test-mfind"))
 
@@ -92,7 +93,7 @@
 
 (define (test-options)
   (test-begin "test-options")
-  (let ((opts (options)))
+  (let ((opts %options))
     (test-assert (>= (length opts) 4))
     (test-equal (assoc-ref opts 'quiet) #f)
     (test-equal (assoc-ref opts 'debug) #f)
@@ -102,11 +103,22 @@
 
 (define (test-helpers)
   (test-begin "test-helpers")
-  (test-equal 1750077792 (iso-date->time-t "2025-06-16T12:43:12"))
+  (setenv "TZ" "Europe/Helsinki")
-  (test-equal 1750075200 (iso-date->time-t "2025-06-16T12"))
+  (tzset)
+  (test-equal 1750077792 (string->time "2025-06-16T15:43:12" #:utc? #f))
+  (test-equal 1750077792 (string->time "2025-06-16 12:43:12" #:utc? #t))
+  (test-equal 1750075200 (string->time "2025-06-16  12" #:utc? #t))
 
-  (test-equal "2025-06-16T12:43:12" (time-t->iso-date 1750077792))
+  (test-equal "2025-06-16 12:43:12" (time->string 1750077792 #:utc? #t))
-  (test-equal "                   " (time-t->iso-date #f))
+  (test-equal "2025-06-16 15:43:12" (time->string 1750077792 #:utc? #f))
+  (test-equal "12:43:12" (time->string 1750077792 #:utc? #t #:format "%T"))
+
+  ;; (define old-prefs %preferences)
+  ;; (define %preferences '((utc? . #t) (short-date  . "%T %F")))
+  ;; (test-equal "12:43:12 2025-06-16" (time->string 1750077792))
+  ;; (set! %preferences old-prefs)
+
+  (test-equal #f (time->string #f))
   (test-end "test-helpers"))
 
 (define* (main _ #:rest args)

scm/mu-scm.scm

@@ -16,7 +16,6 @@
 
 ;; Note: this Scheme code depends on being loaded as part of "mu scm"
 ;; which does so automatically. It is not a general Guile module.
-
 (define-module (mu)
   :use-module (oop goops)
   :use-module (system foreign)
@@ -77,11 +76,12 @@
 	    header
 
 	    ;; misc
-  options
+	    %options
+;;	    %preferences
 
 	    ;; helpers
-  iso-date->time-t
+	    string->time
-  time-t->iso-date))
+	    time->string))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; some helpers for dealing with plists / alists
@@ -416,39 +416,70 @@ The pattern is mandatory; the other (keyword) arguments are optional.
 
 ;;; Misc
 
-(define (options)
+;; Get an alist with the general options this instance of \"mu\" started with.
-  "Get an alist with the general options this instance of \"mu\" started with.
+;; These are based on the command-line arguments, environment etc., see the
-These are based on the command-line arguments, environment etc., see
+;; mu-scm(1) manpage for details.
-the mu-scm(1) manpage for details.
+;;
+;; The alist maps symbols to values; a value of #f indicates that the value is at
+;; its default.
+%options ;; defined in c++
 
-The alist maps symbols to values; a value of #f indicates that the value
+;; Alist of user-preferences.
-is at its default."
+;;
-  %options)
+;; - short-date: a strftime-compatibie string for the display
+;;               format of short dates.
+;; - utc?       : whether to assume use UTC for dates/times
+(define %preferences
+  '( (short-date  . "%F %T")
+     (utc?        . #f)))
+;; XXX; not exposed yet. Perhaps we need a "fluid" here?
+
+(define (value-or-preference val key)
+  "If VAL is the symbol 'preference, return the value for KEY from %preferences.
+Otherwise, return VAL."
+  (if (eq? val 'preference)
+      (assoc-ref %preferences key)
+      val))
 
 ;;; Helpers
 
-(define* (iso-date->time-t isodate)
+(define* (string->time datestr #:key (utc? 'preference))
-  "Convert an ISO-8601 ISODATE to a number of seconds since epoch.
+  "Convert an ISO-8601-style DATESTR to a number of seconds since epoch.
+(like time_t, (current-time).
 
 ISODATE is a string with the strftime format \"%FT%T\", i.e.,
 yyyy-mm-ddThh:mm:ss or any prefix there of. The 'T', ':', '-' or any non-numeric
 characters re optional.
 
-ISODATE is assumed to represent some UTC date."
+UTC? determines whether ISODATE should be interpreted as an UTC time.
-  (let* ((tmpl "00000101000000")
-	 (isodate (string-filter char-numeric? isodate)) ;; filter out 'T' ':' '-' etc
-	 (isodate					 ;; fill out isodate
-	  (if (> (string-length tmpl) (string-length isodate))
-	      (string-append isodate (substring tmpl (string-length isodate)))
-	      isodate)))
-    ;;(format #t "~a\n" isodate)
-    (car (mktime (car (strptime "%Y%m%d%H%M%S" isodate)) "Z"))))
 
-(define-method (time-t->iso-date time-t)
+The input date format is fixed."
-  "Convert a time_t (second-since-epoch) value TIME-T to an ISO-8601
+ ;; XXX If not set, read the default from the %preferences variable.
-string for the corresponding UTC time.
+  (let* ((utc? (value-or-preference utc? 'utc?))
+	 (tmpl "00000101000000")
+	 (datestr (string-filter char-numeric? datestr)) ;; filter out 'T' ':' '-' etc
+	 (datestr					 ;; fill out datestr
+	  (if (> (string-length tmpl) (string-length datestr))
+	      (string-append datestr (substring tmpl (string-length datestr)))
+	      datestr))
+	 (sbdtime (car (strptime "%Y%m%d%H%M%S" datestr))))
+    (car (if utc?
+	     (mktime sbdtime "UTC")
+	     (mktime sbdtime)))))
 
-If TIME-T is #f, return an empty string of the same length."
+
+(define* (time->string time-t #:key (format 'preference) (utc? 'preference))
+  "Convert a time_t (second-since-epoch) value TIME-T into a string.
+
+FORMAT is the strftime-compatible format-string UTC? determines whether to use
+UTC time.
+
+ If TIME-T is #f, return #f."
+;; If not specified, both are determined from %preferences ('short-date
+;; and 'utc?, respectively).
+  (let* ((format (value-or-preference format 'short-date))
+	 (utc? (value-or-preference utc? 'utc?)))
     (if time-t
-      (strftime "%FT%T" (gmtime time-t))
+	(let ((t (if utc? (gmtime time-t) (localtime time-t))))
-      "                   "))
+	  (strftime format t))
+	#f)))

scm/mu-scm.texi

@@ -94,6 +94,7 @@ Appendices
 
 Indices
 * Procedure Index::
+* Variable Index::
 
 @end menu
 
@@ -681,30 +682,56 @@ For example:
 @node Miscellaneous
 @section Miscellaneous
 
-@deffn {Scheme Procedure} options
+@defvar %options
-@end deffn
+@end defvar
 
-This yields an association-list (alist) of general options passed to @command{mu
+An association-list (alist) of general options passed to @command{mu scm} or
-scm}. Values at @t{#f} indicate that the value is at its default.
+their default values.
 @lisp
- (options)
+ %options
 => ((mu-home . #f) (quiet . #f) (debug . #f) (verbose . #f))
 @end lisp
 
+@c @defvar %preferences
+@c @end defvar
+
+@c An association list (alist) of user-preferences that influence interactive use.
+@c E.g., the way how certain things are displayed. The alist maps symbols to values:
+@c @itemize
+@c @item @code{short-date}
+@c a @code{strftime}-compatible string for the display format of short dates.
+@c @item @code{utc?}
+@c boolean, whether to assume UTC for dates/times, such as for @code{string->time} and @code{time->string}
+@c @end itemize
+
+@c @lisp
+@c %preferences
+@c  ((short-date-format . "%F %T") (input-utc? . #f) (output-utc? . #f))
+@c @end lisp
+
 @node Helpers
 @section Helpers
 
-@deffn {Scheme Procedure} iso-date->time-t iso-date
+@deffn {Scheme Procedure} string->time timestr [#:utc? (assoc-ref %preferences 'utc?)]
 @end deffn
-Convert some ISO-8601 compatible time-point (assuming UTC) to a
+Convert some ISO-8601-style time-string to a seconds-since-epoch @t{time_t}
-seconds-since-epoch @t{time_t} value. @var{iso-date} is expected to be in the
+value. @var{timestr} is expected to be in the @t{strftime}-format @t{%F%T}, or a
-@t{strftime}-format @t{%F%T}, or a prefix thereof. Non-numerical characters are
+prefix thereof. Non-numerical characters are ignored.
-ignored.
 
-@deffn {Scheme Procedure} time-t->iso-date time-t
+You can influence whether UTC is assumed using the optional @code{#:utc?}
+parameter. The input time/date format is fixed.
+@c which uses @code{%preferences} for its default.
+
+@deffn {Scheme Procedure} time->string
+                       [#:format (assoc-ref %preferences 'short-date)]
+                       [#:utc? (assoc-ref %preferences 'utc?)]
 @end deffn
-Convert a @t{time_t} value to an ISO-8601 compatible string (assuming UTC). If
+Convert a @t{time_t} value (``seconds-since-epoch'') to a string. The optional
-@var{time_t} is @t{#f}, return an empty string of the same length.
+@code{#:format} parameter (an @code{strftime}-compatible string) determines the
+output format, while the @code{#:utc?} determines whether to use UTC.
+@c Defaults are determined by the @code{%preferences} variable.
+
+If @var{time_t} is @t{#f}, return @code{#f}.
 
 @node GNU Free Documentation License
 @appendix GNU Free Documentation License
@@ -715,8 +742,16 @@ Convert a @t{time_t} value to an ISO-8601 compatible string (assuming UTC). If
 @node Procedure Index
 @unnumbered Procedure Index
 
-This is an alphabetical list of all the procedures and macros in @t{mu-scm}.
+This is an alphabetical list of all the public procedures and macros in @t{mu-scm}.
 
 @printindex fn
 
+@page
+@node Variable Index
+@unnumbered Variables Index
+
+This is an alphabetical list of all the public variables @t{mu-scm}.
+
+@printindex vr
+
 @bye