Behaviour of TagUnset
- To: mathgroup at christensen.Cybernetics.NET
- Subject: [mg278] Behaviour of TagUnset
- From: Jason Harris <physjfh at phys.canterbury.ac.nz>
- Date: Sun, 4 Dec 1994 23:35:58 +1300 (NZDT)
Hi Mathgroupers, I have a question on the function TagUnset. I have been playing around and have found the following odd behaviour. Consider the following: ----------------- In[1]:= ClearAll[p]; Default[p] :=h; p /: f[p[x]]:=x^2; ?p Global`p f[p[x]] ^:= x^2 Default[p] := h ----------------- Now TagUnset works fine together with Literal on UpValues and DownValues as follows ----------------- In[5]:= TagUnset[p, Literal @ f @ p @ x] In[6]:= ?p Global`p Default[p] := h ----------------- But with Default Mathematica complains as follows ----------------- In[7]:= TagUnset[p, Literal @ Default @ p] Unset::norep: Assignment on p for Default[p] not found. Out[7]= $Failed In[8]:= ?p Global`p Default[p] := h ----------------- One can get around this problem simply by omitting the Literal In[9]:= TagUnset[p, Default @ p] but I would have thought that the Literal in the above would have been fine. Can anyone explain this? Thanks, Jason Harris Physics Department University of Canterbury New Zealand