Fossil Wrapper

   set usertag ""
   set rgxdate {^=== [0-9-]+ ===$}
   set rgxtime {^\d\d:\d\d:\d\d}
   set rgxrev {\[([a-f\d]{10})([^\]]*)\]}
   set rgxuser {\(user: .*\)}
   set cnt 0
   set prepend ""
   set maxrev [dict size $revnums]

   foreach record $records {
      # first get rid of the all leading/trailing whitespace and line feeds:
      set record [string trim $record]

      if {[regexp $rgxdate $record]} {
         # the `date' information is extracted and then prepended to the suitable checkins
         set date [regsub {(=== )(.*)( ===)} $record {\2}]
      } elseif {[regexp $rgxrev $record]} { # this line contains a checkin message
         # extract relevant fields:
         regexp $rgxtime $record time
         regexp $rgxrev  $record rev
         regexp $rgxuser $record usertag

         # now reduce `record' to the checkin message:
         regsub " $rgxuser" $record "" record
         regsub "$time "    $record "" record
         regsub "$rgxrev "  $record "" record

         # determine relative revision number:
         set numrev [expr { $maxrev - [dict get $revnums $rev] }]:

         incr cnt
         if {$cnt > 1} {set prepend "\n"}

         lappend out "$prepend$date $time $numrev$rev $record $usertag"
      } else {
         # should be a file status line as delivered by `-showfiles' (since
         # it is neither matching `rgxdate' nor `rgxrev'). append after
         # stripping white space and separate by appending a full stop.
         lappend out " [string trim $record]."
      }
   }
   return [lappend out \n]
}

proc computeRevnums {params} {
#-----------------------------------------------------------------------
# generate a dictionary of SHA1 keys vs. "reverse" revision numbers 
# (last checkin = 1)
#-----------------------------------------------------------------------
   set huge    1000000        ;# should not be reached by most projects ...
   set revcnt  0

   set rgxtime {^\d\d:\d\d:\d\d}
   set rgxrev  {\[([a-f\d]{10})([^\]]*)\]}
   set rgxrepo {\-R[[:blank:]]+.+} 
   set repo    ""

   regexp $rgxrepo $params repo
   catch {exec fossil timeline -n $huge {*}$repo} timeline
   set lines [split $timeline \n]




   foreach line $lines {
      if {[regexp $rgxtime $line]} {
         incr revcnt
         regexp $rgxrev $line rev
         dict set revnums $rev [expr {$revcnt}]
      }
   } 
   return $revnums
}

proc preparse argv {
# -------------------------------------------------------------------

   set rgxrevnum {[[:digit:]]+(:[[:digit:]]+)?}
   set rgx $rgx$rgxrevnum

   # without `-r' argument we can return already:
   if {![regexp $rgx $params revarg]} {return $params}

   set hash2num [computeRevnums {}]
   set dim [dict size $hash2num]

   # exchange keys and values in the above dictonary. at the same time,
   # strip the square brackets around the hash value:
   dict for {key val} $hash2num {
      regexp {[a-f\d]{10}} $key sha1
      dict set num2hash [expr {$dim - $val}] $sha1
   }

   # translate rev. numbers to sha1 hashes and construct the 
   # required `diff' arguments:
   regexp $rgxrevnum $revarg numbers
   set revs [split $numbers :]
   set to {}