evaluating math w/o recompile

[anthony zador]

I have functions of the form

double f(V,t) 
  double V,t;
{
  return (some math function involving about a 
       line of exp, division, mult and add
       on V, t)
}

I use these functions to construct a table:

Table(f, table_array)
   ptr_to_fun f;
   double_array table_array;
{
  construct table_array by evaluating f[n]
}
I would like to be able to specify the form of the function f
at *run time* (no recompiles). That is, i would like 
to place a line of math
in some file and have the program read it in and evaluate it.

For example, my fnct could be
    1.6/(1+exp(-0.072*(V-5.0)))
or 
   0.02*(V+8.69)/(exp((V+8.69)/5.36)-1)         



I have played around with "hoc", the high order calculator
described in the Unix Programming Environment by K&P, but that seems
like overkill for this task. Is there a simpler way?


I'd appreciate any ideas.

--Tony Zador
zador at yale-sun3-nebula.arpa 
zador at nebula.sun3.cs.yale.edu