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SISAL

Language type:

F - Functional or lambda-based

Description:

SISAL is a functional programming language designed for parallel processing. The name SISAL stands for Streams and Iteration in a Single Assignment Language. It is intended for use programming scientific application on multi-processor supercomputers, and for educational use in teaching parallel programming.
The lexical structure of SISAL is similar to that of Pascal. The syntax is simple and uniform, with special keywords for controlling arrays and iteration. Data types in SISAL include integers, reals, strings, multi-dimensional arrays, and records. Control structures in SISAL look deceptively familiar, but have functional rather than procedural semantics. The semantics of the 'for' loop are particularly rich, although somewhat complicated. SISAL is strongly typed, and no implicit conversions are supported; all data type casting must be explicitly specified by the programmer. Other programming features of SISAL include multi-arity functions, user-defined data types, sophisticated array handling, a large library of built-in math functions, and streams-oriented I/O.
The mathematical foundations of SISAL are similar to that of other functional languages: all computations produce results, and computations do not produce side-effects. Further, SISAL programs are guaranteed to be deadlock-free and determinate, even in parallel environments.
The main SISAL implementation is an optimizing compiler with back-ends targetted for different parallel architectures. There are also subset SISAL interpreters for beginner use. All SISAL language implementations are free. It runs one a fair variety of platforms, including many UNIX systems, PC, Macintosh, and Cray and Intel supercomputers. Documentation for the language and its compilers is easily available on the WWW.

Origin:

John Feo et al, Lawrence Livermore National Laboratory, 1990.

See Also:

Lucid    Clean    ML    Pascal   

Remarks:

SISAL was designed to allow the compiler to make fine-grained decisions about parallelism. The LLNL optimizing SISAL compiler uses dataflow graphs to identify dependencies and order computations. In performance tests, parallelized SISAL programs were faster than comparable parallelized FORTRAN programs on several supercomputer platforms.
As in many other functional languages, I/O in SISAL is somewhat rigid and still problematic. SISAL does support, partially, an I/O data format called Fibre; this facility is still under development as of late 1997.
SISAL is suitable for use on a large class of mathematical problems, but it's adoption outside of LLNL seems to be spotty.

Links:

A Tutorial Introduction to SISAL

SISAL Main FTP download area

Sisal90 User's Manual

Date:

Last updated 11/7/99

Sample code:

% A simple example of using SISAL arrays,
% adapted from various sample exercises in the
% SISAL tutorial by John Feo.

define main

type Matrix = array [ array [ real ] ]

% generate a square matrix where element [n,m]
% is set to n   m
function gensquare(siz : integer
                                 returns Matrix )
   for i in 1,siz cross j in 1,siz
        returns array of real(i)   real(j)
   end for
end function

% perform one step of a relaxation, average each
% element with its eight nearest neighbors
function relax ( a : Matrix returns Matrix )

for row in a at i cross elt in row at j
   avg := (elt   a[i, j-1]   a[i, j 1]  
           a[i 1, j-1]   a[i 1, j]   a[i 1, j 1]  
           a[i-1, j-1]   a[i-1, j]   a[i-1, j 1]) / 9.0
returns array of avg
end for

end function

% test the generator and relax function

function main(returns Matrix)

let a1 := gensquare(5)  in a1
end let

end function

Descriptions in this dictionary are ©1997-99 Neal Ziring. Some examples copyright of their respective authors. Some technologies and languages are trademarked. Permission to copy descriptions is granted as long as authorship credit is preserved.

Comments on this dictionary, corrections and suggestions, are all welcome. Please use email, the address is ziring@home.com