REVERSE‐DIR - KVonGit/zil-stuff GitHub Wiki

<ROUTINE REVERSE-DIR (DIR)
  <COND
    (<==? .DIR ,P?NORTH> ,P?SOUTH)
    (<==? .DIR ,P?SOUTH> ,P?NORTH)
    (<==? .DIR ,P?EAST> ,P?WEST)
    (<==? .DIR ,P?WEST> ,P?EAST)
    (<==? .DIR ,P?UP> ,P?DOWN)
    (<==? .DIR ,P?DOWN> ,P?UP)
    (T ,P?NOWHERE)
  >
>