[Nmh-workers] Request for sortm feature to implement arbitrary message ordering

[norm]

This request is for sortm to have a '-program path-name' feature

path-name would name a command which would be invoked by sortm. It would be
given 2 arguments, full path names of messages. Its standard output would
either

    begin with "+", meaning that the first argument is to be regarded as
    greater than the second,

    or

    begin with '-", meaning that the first argument is to be regarded as less
    then the second

     or

     be empty  or begin with some other character, meaning that sortm
     would use its usual mechanisms to relate the two arguments.

The command's standard error would be piped to sortm's standard error.

A non-zero exit status would be a fatal to sortm.

sortm would assume, without checking, that the ordering imposed by the command
was transitive and anti-symmetric. That is, that a<b and b<c implies a<c and
that a<b implies b>a.

If there were several  '-program path-name' pairs the last one would be used.
-noprogram would cancel any previous '-program path-name' pair.


  Norman Shapiro