In ACL2 we have adopted Common Lisp as the basis of our modeling language.
If you have already read our brief note on Common Lisp and recall the example
app, please proceed. Otherwise click here for an
exceedingly brief introduction to Common Lisp and then come back here.
In Common Lisp it is very easy to write systems of formulas that manipulate discrete, inductively constructed data objects. In building a model you might need to formalize the notion of sequences and define such operations as concatenation, length, whether one is a permutation of the other, etc. It is easy to do this in Common Lisp. Furthermore, if you have a Common Lisp ``theory of sequences'' you can run the operations and relations you define. That is, you can execute the functions on concrete data to see what results your formulas produce.
If you define the function
app as shown above and then type
(app '(A B) '(C D E))in any Common Lisp, the answer will be computed and will be
(A B C D E).
The executable nature of Common Lisp and thus of ACL2 is very handy when producing models.
But executability is not enough for a modeling language because the purpose of models is to permit analysis.
Click here to continue.