Mma In and Out

*To*: MathGroup at yoda.physics.unc.edu*Subject*: Mma In and Out*From*: fransm at info.win.tue.nl (Frans Martens)*Date*: Thu, 10 Dec 92 15:41:48 +0100

An "In and Out" problem The problem below is subtracted from a more complicated Mma problem. Ingredients are a function f and a test testq: In[1]:= f[a_?testq]:=aap In[2]:= f[u] Out[2]= f[u] In[3]:= testq[u]=True Out[3]= True In[4]:= Out[2] Out[4]= f[u] This doesn't surprise me too much. The variable u itself hasn't changed. In[5]:= In[2] Out[5]= f[u] This result seems strange to me. In[2] has a delayed value of the second input line. The questions are: (1) How can an inexperienced Mma user evaluate In[2] (or Out[2] ) again in such a way that the correction ( In[3] ) is effective? (2) Why isn't In[2] evaluated anew? What are the ideas behind this setup of the In object? Remark: I know that u/: test[u]=True would not have caused problems. But that is not the point. Frans Martens University of Technology Eindhoven The Netherlands fransm at win.tue.nl