Machine Tongues VII

Abstract

Lisp is the second-oldest programming language currently in use; it is predated only by Fortran. Lisp is and always has been the principal language of the artificial intelligence (AI) community. The ideas behind the language are very innovative-and for a very good reason. The task of emulating human intelligence is without a doubt very difficult. The degree of success that a programmer can expect depends in a significant way on the power and flexibility of his or her programming language. If the application we set for ourselves is impossibly hard (as farsighted AI projects will surely be for a long time to come) we will place a great premium on attributes of the programming language that reduce the apparent complexity of the problem. We would expect more innovative ideas in language design to come from experience in AI research than, say, the design of inventory-control systems or signal-processing programs. Lisp embodies important principles that make programs (any programs) easier to write. Long experience has demonstrated that Lisp is an eminently practical programming language. Considering all this, it is somewhat puzzling to researchers in AI why Lisp is so little known and so often misunderstood by the computer community at large. The development of Lisp began at M.I.T. around 1956 under the direction of John McCarthy (currently at the Stanford Artificial Intelligence Laboratory). The original ideas came from several sources: recursive function theory, the lambda calculus, Polish notation (all of which predate real computers) and the concept of list structure that was developed by Newell and Simon for AI research. The original implementations of Lisp were cumbersome and slow. This no doubt contributed to the current impressions of many people that Lisp is a toy rather than a real programming language. This is anything but true. Current Lisp compilers are capable of producing object code as efficiently as the compilers for languages like Fortran or Pascal when the Lisp language is restricted to a subset equivalent to these in power. Of course, Lisp is capable of much