pushd/popd/dirs for es

[Noah Friedman <friedman@gnu.ai.mit.edu>]

Here is a pwd prettifier (that substitutes ~ for $home in the pathname)
that could conceivably call no external programs.  It could be generalized
to take a list of arguments or at least one abitrary argument.  For now it
just uses `pwd (which, if you use my pushd/popd frobs, is not an external
program). 


fn pwd-pretty \
{
   let (pwd = `pwd; pwdl = ; homel =)
     {
       ~ $pwd $home && { echo '~'; return 0 }
       ~ $pwd $home^* || { echo $pwd; return 0 }

       pwdl = <={ %split '/' $pwd }
       homel = <={ %split '/' '.' $home }
       pwdl = $pwdl($#homel ...)
       echo <={ %flatten '/' '~' $pwdl }
     }
}