Your shortened version won't work, actually, for two reasons:
1. Unless the WorldFrame is different from all other frames in this regard, you always need to pass the frame itself as the first argument to any frame method. So in your example, you'd need:
Code:
C(W)S(W,"TOPLEFT",l,t)S(W,"BOTTOMRIGHT",r,b)
(Also, local-ing the ClearAllPoints call is somewhat redundant if it's only invoked once)
2. You can't access a variable's new value in the same assignment statement you define it in.
Code:
> local W,C,S=WorldFrame,W.ClearAllPoints,W.SetPoint
Error: attempt to index global 'W' (a nil value)
Fixed version: (top,bottom,left,right in that order)
Code:
/run local t,b,l,r,W,S=100,200,50,50 W=WorldFrame S=W.SetPoint W:ClearAllPoints()S(W,"BOTTOMLEFT",l,b)S(W,"TOPRIGHT",-r,-t