SNOBOL
Encyclopedia : S : SN : SNO : SNOBOL
- This article is about the SNOBOL programming language; for information about the cleaning product see SnoBol (cleaner).
During the 1950s and 1960s there was a flourishing of interest in special-purpose computer languages. SNOBOL was one of a number of text-string-oriented languages, and one of the more successful; others included COMIT and TRAC.
SNOBOL was widely used in the 1970s and 1980s as a text manipulation language in the humanities, but in recent years, its popularity has faded as newer languages such as Awk and Perl have made string manipulation by means of regular expressions popular; it is now mostly a special interest language used mainly by enthusiasts, and new implementations are rare. However, SNOBOL's pattern matching algorithm is in many ways more powerful than regular expressions. The classic implementation was on the PDP-10; it has been used to study compilers, formal grammars, and artificial intelligence, especially machine translation and machine comprehension of natural languages. The original implementation was on an IBM 7090 at Bell Labs, Holmdel, N.J. SNOBOL4 was specifically designed for portability; the first implementation was on an IBM 7094 but it was rapidly ported to many other platforms.
SNOBOL was originally called SEXI - String EXpression Interpreter.
The SNOBOL4 (StriNg Oriented symBOlic Language number 4) version is the fourth and final incarnation of such a series of special purpose programming languages for character string manipulation.
The SNOBOL4 variant of the language supports a number of built-in data types, such as integers and limited precision real numbers, strings, patterns, arrays, and tables, and also allows the programmer to define additional data types and new functions. SNOBOL4's programmer-defined data type facility was advanced at the time (it preceded, and resembles, Pascal's "records" and C's "structs.").
SNOBOL4 stands apart from the mainstream programming languages of that time by having patterns as a first-class data type (i.e. a data type whose values can be manipulated in all ways permitted to any other data type in the programming language) and by providing operators for pattern concatenation and alternation. Strings generated during execution can be treated as programs and executed.
A SNOBOL pattern can be very simple or extremely complex. A simple pattern is just a text string (e.g. "ABCD"), but a complex pattern may be a large structure describing, for example, the complete grammar of a computer language.
SNOBOL provides the programmer with a rich assortment of features including some rather exotic ones. As a result it is possible to use SNOBOL as if it were an object-oriented language, a logical programming language, a functional language or a standard imperative language by changing the set of features used to write a program. It also concatenates strings that are simply placed next to each other in a statement. It keeps strings in a memory heap, and frees programmers from concerns about memory allocation and management for strings.
It is normally implemented as an interpreter because of the difficulty in implementing some of its very high-level features, but there is a compiler, the SPITBOL compiler, which provides nearly all the facilities that the interpreter provides.
The Icon programming language is a descendant of SNOBOL4.
Hello World
OUTPUT = 'Hello World!' END
See also
- SPITBOL (compiled implementation of SNOBOL4)
- Icon programming language (a descendant)
- Unicon programming language (a descendant of Icon)
Further reading
- Griswold, Ralph E., J. F. Poage, and I. P. Polensky. The SNOBOL 4 Programming Language. Englewood Cliffs, NJ: Prentice Hall, 1968 (ISBN 0138153736).
- Hockey, Susan M. Snobol Programming for the Humanities. New York: Clarendon Press; Oxford: Oxford University Press, 1985 (ISBN 0198246765).
External links
- [Phil Budne's page of resources]
- [History of SNOBOL4]
- [Open Directory Project Category for Snobol]
- [Catspaw, Inc. offers implementations of and support for SNOBOL4]
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