48 Chapter 2 Evolution of the Major Programming Languages
list-processing instructions were included. Another factor that kept the IPL
languages from becoming popular was their implementation on the obscure
Johnniac machine.
The contributions of the IPL languages were in their list design and their
demonstration that list processing was feasible and useful.
IBM became interested in AI in the mid-1950s and chose theorem prov-
ing as a demonstration area. At the time, the Fortran project was still under-
way. The high cost of the Fortran I compiler convinced IBM that their list
processing should be attached to Fortran, rather than in the form of a new
language. Thus, the Fortran List Processing Language (FLPL) was designed
and implemented as an extension to Fortran. FLPL was used to construct a
theorem prover for plane geometry, which was then considered the easiest area
for mechanical theorem proving.2.4.2 LISP Design Process
John McCarthy of MIT took a summer position at the IBM Information
Research Department in 1958. His goal for the summer was to investigate
symbolic computations and to develop a set of requirements for doing such
computations. As a pilot example problem area, he chose differentiation of
algebraic expressions. From this study came a list of language requirements.
Among them were the control flow methods of mathematical functions: recur-
sion and conditional expressions. The only available high-level language of the
time, Fortran I, had neither of these.
Another requirement that grew from the symbolic-differentiation inves-
tigation was the need for dynamically allocated linked lists and some kind of
implicit deallocation of abandoned lists. McCarthy simply would not allow his
elegant algorithm for differentiation to be cluttered with explicit deallocation
statements.
Because FLPL did not support recursion, conditional expressions, dynamic
storage allocation, or implicit deallocation, it was clear to McCarthy that a new
language was needed.
When McCarthy returned to MIT in the fall of 1958, he and Marvin
Minsky formed the MIT AI Project, with funding from the Research Labora-
tory for Electronics. The first important effort of the project was to produce
a software system for list processing. It was to be used initially to implement
a program proposed by McCarthy called the Advice Taker.^3 This application
became the impetus for the development of the list-processing language LISP.
The first version of LISP is sometimes called “pure LISP” because it is a purely
functional language. In the following section, we describe the development of
pure LISP.- Advice Taker represented information with sentences written in a formal language and used
a logical inferencing process to decide what to do.