[Therion] changing wall symbols

[Andrew Atkinson]

Hello

On some scales the wall:debris and blocks does not work very well. So I
thought that I would change the symbol.

So I have been using

code metapost
  let p_gradient = p_entrance_UIS;

Which works fine.

so copying that I tried

code metapost
  let l_wall_debris = l_wall_UIS;

Which had no effect. With a bit more playing I discovered I could not
change any wall

things like

code metapost
  let l_wall = l_floorstep_UIS;



further experiments showed I could not change any line symbol

code metapost
  let l_overhang = l_wall_UIS;

one problem is that an error is not generated if you make a typo so I
cannot tell if I have the right identifiers.

What am I doing wrong?

Andrew