Fortran

Fortran (also FORTRAN) is a programming language originally developed in the
1950s and still in use today. The name is short for "Formula Translation".
Early versions of the language were known as FORTRAN, but the capitalization
has been dropped in newer revisions beginning with Fortran 90. The official
language standards now refer to the language as "Fortran".

Fortran is mainly used for scientific computing and numerical analysis.
Although originally a procedural language, recent versions of Fortran have
included some features to support object-oriented programming.

The first FORTRAN compiler was developed for the IBM 704 in 1954-57 by an
IBM team led by John W. Backus. This was an optimizing compiler, because the
authors reasoned that no one would use the language if its performance was
not comparable to assembly language.

The language was widely adopted by scientists for writing numerically
intensive programs, which encouraged compiler writers to produce compilers
that generate faster code. There are many vendors of high performance
Fortran compilers today. Many advances in the theory and design of compilers
were motivated by the need to generate good code for Fortran programs.

Several revisions of the language have appeared, including the well-known
FORTRAN IV (also known as FORTRAN 66), FORTRAN 77, and Fortran 90. The most
recent formal standard for the language, published in 1997, is known as
Fortran 95. IBM's versions were never as popular as those developed by
others, which was especially true of FORTRAN IV -- WATFOR, the version of
FORTRAN IV developed at the University of Waterloo, Canada, was universally
preferred because it produced better reports of compilation errors. The
software for automatically generating flow charts from FORTRAN programs was
also developed outside IBM.

Initially, the language relied on precise formatting of the source code and
heavy use of statement numbers and goto statements. These quirks have been
removed from newer versions of the language. Successive versions also
introduced 'modern' programming concepts, such as source code comments and
output of text, IF-THEN-ELSE (in FORTRAN 77), recursion (in Fortran 90), and
parallel constructs, while still attempting to maintain Fortran's 'lean'
profile and high performance. Among the most popular specialized
Fortran-based languages were SAS, for generating statistical reports, and
SIMSCRIPT, for simulating processes involving queuing.

Vendors of high performance scientific computers (Burroughs, CDC, Cray, IBM,
Texas Instruments, ...) added extensions to Fortran to make use of special
hardware features such as: instruction cache, CPU pipeline, vector arrays,
etc. For example, one of IBM's Fortran compilers (H Extended IUP) had a
level of optimization which reordered the machine code instructions to keep
several internal arithmetic units busy at the same time. Another example is
CFD, a special 'version' of Fortran designed specifically for the ILLIAC IV
supercomputer, running at NASA's Ames Research Center. These extensions have
either disappeared over time or had elements incorporated into the main
standard; the major remaining extension is OpenMP, which is a cross-platform
extension for shared memory programming. One new extension, CoArray Fortran,
is intended to promote parallel programming.

As what was basically a first attempt at designing a high-level language,
the language's syntax is regarded as arcane by many programmers who learned
more modern languages. It is difficult to write a lexical analyser for, and
one-character mistakes can lead to runtime errors rather than compilation
errors if more recent constructs such are not used. Some of the earlier
versions, particularly, lacked facilities that would be regarded as useful
in modern machines, such as dynamic memory allocation. At the same time, the
syntax of Fortran has been tuned to scientific and numerical work, and many
of its deficiencies have been addressed in more recent versions. For
example, Fortran 95 has very short commands for performing mathematical
operations on matrices and arrays which not only greatly improves program
readability but also provides useful information to the compiler to enable
it to vectorize operations. For these reasons, Fortran is not often used
outside scientific and engineering numerical analysis, but remains the
language of choice for high performance numerical computing.

Standards

The two standards below reflect the current Fortran implementations.

   * ANSI X3.198-1992 (R1997). Title: Programming Language "Fortran"
     Extended. Informally known as Fortran 90. This standard was published
     by ANSI.
   * ISO/IEC 1539-1:1997. Title: Information technology - Programming
     languages - Fortran - Part 1: Base language. Informally known as
     Fortran 95. There are a further 2 parts to this standard. Part 1 has
     been formally adopted by ANSI.

Code Sample (Hello, World)

 c
 c   Hello, world.
 c
       Program Hello


       implicit none
       logical DONE


       DO while (.NOT. DONE)
         write(*,10)
       END DO
    10 format('Hello, world.')
       END