Aspects of ACL2 User Interaction
Matt Kaufmann (joint work with J Strother Moore), UITP'08, August, 2008
Users of the ACL2
theorem prover typically interact with the system in many ways
beyond submitting definitions and proving theorems. This talk will
show some examples to provide a sense of the diversity of ACL2 user
interaction. A few more in-depth examples may be found in the TPHOLS
2008 ACL2 tutorial.
Certainly we will consider the narrow sense of "user interface" as
control of input and output. Users traditionally interact efficiently
with ACL2 through Emacs, and we will demonstrate some Emacs
customizations provided with the system. More recently, two
Eclipse-based interfaces have been developed by other groups for
teaching purposes: the ACL2
Sedan (ACL2s) and DrACuLa. Beyond the
choice of editor (or terminal) is the issue of how to control ACL2
output, traditionally through generated English commentary. A proof-tree
display illustrates proof structure and provides help for navigating
that commentary. But a recent gag-mode
enhancement is probably much more effective for debugging failed proof
Other useful output includes error and warning messages, which often
point to user documentation. But ACL2 supports effective user
interaction in ways beyond the above notions of input/output control.
A separate question, not addressed in this talk, is how to communicate
proof results effectively to non-users. Our focus is on interface
support for effective usage.
- Proof commands include not only definitions
but also scoping
can affect the course of proof attempts, and (less often) are dynamically
generated by user programs (roughly in analogy to tactics in
- Users can direct how proved theorems are to be stored as rules,
by default as (conditional, congruence-based) rewrite
rules. Syntactic control mechanisms can affect the applicability of
- The system state can be affected by setting various modes. Two
examples include a program
mode, which allows the user to write programs that need not
terminate but can be used in macros,
and a backchain
limit for rewriting.
management commands include undoing,
and querying the state.
- Proof assistance is provided by two break/trace
utilities for the rewriter; an interactive
goal manager; and a report
mechanism that can show "expensive" rules.
- The programming
interface provides features to bridge the gap between the user and
the computing engine, such as Lisp-independent trace
utilities and verifiable
alternative function bodies. This interface also makes
available powerful Lisp features including packages
and other single-threaded
objects are supported efficiently with an applicative semantics.
mechanism provides a powerful, though less automatic, alternative to
types that is separate from the logical content of definitions.
- Users can interactively extend the system's capabilities by
of logical definitions and theorems, as well as system utilities and
even (through trust
tags) system modifications.
- A clause-processor
mechanism provides an interface through which the user connects ACL2
with another tool.