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From: sheaf@helios (Sheaf)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Programming Question
Summary: Defining functions by user input.
Message-ID: <142295@unix.cis.pitt.edu>
Date: 20 Jun 91 16:47:15 GMT
Sender: news@unix.cis.pitt.edu
Distribution: usa
Organization: University of Pittsburgh, Department of Physics and Astronomy
Lines: 25


Here is a programming problem that's been driving me nuts for some time now,
and I'm hoping someone can shed some light on this for me.  I use several
languge compilers including Pascal and several versions of BASIC, but it's
sort of unimportant since my problem is the same with all of them.

I am developing some mathematical software utilities, and very simply, I
want the user to be able to enter a function on the screen and have it 
graphed by the program.  Sounds simple enough, and I have some great 2D
and 3D graphing routines, but the problem is this: in order to graph something,
you have to define it as a function, and while the coefficients in the 
DEFINE statement can be variables, the expression itself has to be hardcoded.
Also, the DEFINE statements can't define a function from a string 
variable with the expression stored in it.  

So, to put it simply, is there any way (in any language) to define a function
bby user input ?  I know it can be done, I have software that does exactly 
this, but for the life of me I can't figure out how.

If you have any tips, please E-mail me.


                                         Steve Sheaffer 
                                         sheaf@groucho.phyast.pitt.edu