( ( testproc
  =   i x y z
    .   out$"Calling testproc"
      & (=~):(=?i:?x:?y:?z)     { initialise variables to 'failure' }
      &   !arg
        : (? (i,?i) ?|?)        { if "i" found, assign value to i. Otherwise just match with no side effect. }
        : (? (x,?x) ?|?)        { if "x" found, assign value to x. Otherwise just match with no side effect. }
        : (? (y,?y) ?|?)        { likewise }
        : (? (z,?z) ?|?)        { likewise }
      & (~!i|put$("   i:=" !i)) { if variable doesn't fail, show its value }
      & (~!x|put$("   x:=" !x))
      & (~!y|put$("   y:=" !y))
      & (~!z|put$("   z:=" !z))
      & put$\n                  { add new line }
  )
& testproc$((x,1) (y,2) (z,3))
& testproc$((x,3) (y,1) (z,2))
& testproc$((z,4) (x,2) (y,3))  { order is not important }
& testproc$((i,1) (y,2) (z,3))
);