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OCR for page 118
Appendix 18
Relation Between
Programming Languages
and Linguistics
EFFECT OF LINGUISTICS ON PROGRAMMING
This effect varies from period to period of programming history
(which is very short) . In pre-Fortran times the effect was al-
most nil since all programming was in machine language and
almost all computation was scientific.
I n the period from Fortran to ALGOL (1956-1960) the connection
was almost totally terminological: words and definitions, but not
theory and technique, were borrowed from linguistics, for ex-
ample, grammar and syntax. The real link was between program-
ming and mathematical logic, as witness the development of ADES
languages based on recursive functions and the development of
several Polish prefix-oriented languages. Syntax analysis during
this period was a collection of ad hoc techniques. Thus the paper
by Sheridan on Fortran~ is enormously complex. Descriptions of
even more complex grammars are much more clearly understand-
able today.
The period from ALGOL to the present shows intense borrowing
of current mathematical linguistic theory, technique, and notation.
The source of this dependency can be traced to the definition of
ALGOL 60 syntax production notation. The similarity between
this notation and the rewriting rules of some linguistic models
caused this theory to be rapidly employed in programming. Still,
it is important to note that the definition of the ALGOL language was
totally inspired by programming considerations (Fortran, LISP),
and not linguistic ones.
The effect of this syntax formalism has been enormous and all
to the good. Thus ALGOL syntax is "essentially" of Type 2. Hence,
parsing mechanisms for Type 2 languages can be applied in the
construction of ALGOL translators. Many of the parsing techniques
employed were, however, discovered by programmers operating
in parallel to, but independent of, similar developments in mathe-
matical linguistics.
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The existence of a theory has made it possible to define vari-
ations on a given grammar that permit the same task specifica-
tion but in a grammar more efficiently parsed (one push-down
stack instead of many, no retracing of paths in a tree of syntax
choices), for example, precedence grammars.
Certainly it is now the case that the design of programming
languages follows a more rational procedure than before because
of mathematical linguistics, and proceeds in the following steps:
A. A set of tasks is isolated and their informal algorithmic
descriptions are specified.
B. The data structures inherent in this class of problems are
isolated and appropriate computer representations are defined.
The natural operators on the data are isolated.
C.
D. A grammar of increasingly complex units is specified, e.g.,
atoms, expressions, statements, and programs.
E. A parser-recognizer is constructed for the grammar.
F. The steps D and E are iterated until a reasonable mixture
of flexibility and efficiency is attained.
G. A semiformal statement of the evaluation of algorithms
described in this language is given, which becomes the basis for
a translation process taking this language into some other given
language (usually machine code).
It is now possible to teach syntax analysis of programming
languages, i.e., the basic knowledge is now available in an organized
form.
It is now possible to construct programs that are general-
purpose syntax analysers in the sense that they parse any program-
ming language of a given type.
EFFECT OF PROGRAMMING ON LINGUISTICS
Since programming is an "applied"' activity and linguistics a more
abstract one, programming has provided linguistics with "real"
models that are sufficiently complicated to permit the development
of diverse theories.
Programming has also led to the definition of linguistic models
possessing a theory of their owns and specifically tailored for use
as programming languages.4
The existence of a body of technique in programming has made
it possible to develop special programming languages for solving
certain linguistic problems, e.g., SNOBOL5 and COMITY.
Similarly, programming, being concerned with a growing set of
demands, provides a pressure on linguistic theory directing it
toward problems particularly relevant to computation, e.g., prob-
lems of efficiency of representation and speed of computation.
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FUTURE RELATIONSHIP BETWEEN
PROGRAMMING AND LINGUISTICS
programming there will be concentration on developing theories
of evaluation, i.e., what is meant by the execution of a program
written in language ~ ? We may call this the sematics of it. Such
studies will replace the present ad hoc development of compiler-
compilers with a theory of their properties and more insight into
the design of computing machines. This is the translation problem
for computer languages.
These languages will become sufficiently complex so that a theory
of their semantics or evaluation will be a sufficiently interesting
model for the equivalent problems arising in natural language
translation.
Similarly, there will be a reverse flow from the development of
semantic theories within natural linguistics into mathematical
linguistic models, which, in turn, will influence programming.
REFERENCES
1. E. K. Blum, "Automatic Digital Encoding System, " NAVORD Rep.
4411 (1956).
2. P. B. Sheridan, "The Arithmetic Translator-Compiler of the IBM
Fortran Automatic Coding System," Commun. Assoc. Computing Mach.
_, 9 (1959).
3. S. Ginsburg and R. H. Gordon, "Two Families of Languages Related
to ALGOL," J. Assoc. Computing Mach. 9, 350 (1962~.
R. W. Floyd, "Syntactic Analysis and Operator Precedence," J. Assoc.
Computing Mach. 10, 316 (1964).
5. D. J. Farber, R. E. Griswold, and I. P. Polonsky, 'iSNOBOL, A String
Manipulation Language," J. Assoc. Computing Mach. 11, 21 (1964).
6. The Research Laboratory of Electronics and the Computation Center,
COMIT Programmers Reference Manual, 2nd ea., The M.I.T. Press,
Cambridge, Mass. (1962).
4.
Bl BLIOGRAPHY
1. R. W. Floyd, IEEE Trans. Electron. Computers 13, 346 (1964). This
bibliography includes subjects related to the syntax of programming
languages insofar as they illuminate the problems of analysis and
synthesis of formally defined programming languages.
120
Representative terms from entire chapter:
linguistic models
