Fossil Wrapper

   # further `diff' arguments.
   # This call is mapped to
   #
   # fsl (g)di ... -r sha1_n (--to sha1_m) ...
   #
   # where `sha1_n, sha1_m' are the sha1 hashes of the respective checkins.
   # ------------------------------------------------------------------------
   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
   }

   # map this interceptor command to `fossil (g)diff'. actually, we use `di'
   # instead of `diff' since only the former will trigger the `diff' filter:
   regsub {^(g?d)f} $params {\1i} params

   # extract the revison number information from `params'. contrary to
   # `fossil' it is acceptable to omit blanks between `-r' and `n:m':
   set rgx { \-r[[:blank:]]*}
   set rgxrevnum {[[:digit:]]+(:[[:digit:]]+)?}
   set rgx $rgx$rgxrevnum

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











   # translate rev. numbers to sha1 hashes and construct the 
   # required `diff' arguments:
   regexp $rgxrevnum $revarg numbers
   set revs [split $numbers :]
   set to {}
   set cnt 0