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From: kerrin@cathedral.cerc.wvu.wvnet.edu (Kerrin Smith)
Newsgroups: comp.lang.c++
Subject: Request for help in simulating an interactive system
Keywords: c++, g++, interactive
Message-ID: <935@babcock.cerc.wvu.wvnet.edu>
Date: 22 Oct 90 18:17:56 GMT
Sender: news@cerc.wvu.wvnet.edu
Lines: 35

I am in the process of developing a constraint management system in G++.  I am 
interested in being able to dynamically load constraints of a form such
as X = Y + Z, where X, Y and Z are variables.  Upon recognizing a variable,
I will create a new "variable" object.  Here is where my problem lies.
I would like to be able to *bind* the variable name, say X, to the newly
created object so that later I can reference it directly simply by using the
name X.

Now, I know that I can store the character string X in the newly created data
structure, however, an exhaustive search through some list would then be 
required for each access.

I could create enough pointers to variables initially and give them names
that I know will occur.  As each variable is created I can point the existing
variable pointer to the appropriate object.  The problem with this is that
I won't know the variable names or how many variables there will be in advance.

The best method I've come up with is to create a hashing function to map
the variable name to the new variable object.  This solution is okay but
it requires a function call for each variable access.  Instead of being able
to say   R = X + Z,   I'll be required to say something like, 
MAP(R) = MAP(X) + MAP(Z).

I know that what I am trying to do is exactly what separates interpreters
from compilers, but it seems as though there must be a more elegant method
to simulating an interactive system.  Any advice or references would be 
greatly appreciated.   

Kerrin Smith
Graduate Student

School: West Virginia University

Work:   Concurrent Engineering Research Center
        Kerrin@cerc.wvu.wvnet.edu