Implementations
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 started on an IBM 7094 in 1966 but completed on an IBM 360 in 1967. It was rapidly ported to many other platforms.
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 Gnat Ada Compiler comes with a package (GNAT.Spitbol) which implements all of the Spitbol string manipulation semantics. This can be called from within an Ada program.
The file editor for the Michigan Terminal System used a pattern language derived from SNOBOL4.
Several implementations are currently available. Macro SNOBOL4 in C written by Phil Budne is a free, open source implementation, capable of running on almost any platform. It is available at http://www.snobol4.org/. Catspaw, Inc. at http://www.snobol4.com/, provides a commercial implementation of the SNOBOL4 language for many different computer platforms, including DOS, Macintosh, Sun, RS/6000, and others. An older version, SNOBOL4+, is now available free from Catspaw. Minnesota SNOBOL4, By Viktors Berstis, the closest PC implementation to the original IBM mainframe version (even including Fortran-like FORMAT statement support) is also free, and is at http://www.berstis.com/snobol4.htm.
Although SNOBOL itself has no structured programming features, a structured extension of SNOBOL called Snostorm existed at University College London (UCL) between 1982 and 1984, and another by Andrew Koenig called Snocone.
The SPITBOL implementation also introduced a number of features which, while not using traditional structured programming keywords, nevertheless can be used to provide many of the equivalent capabilities normally thought of as "structured programming", most notably nested if/then/else type constructs. These features have since been added to most recent SNOBOL4 implementations. After many years as a commercial product, in April 2009 SPITBOL was released as free software under the GNU General Public License.
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