FORTRAN - Language features, Variants of Fortran, Criticisms and rebuttals, Code examples, FORTRAN jokes
Acronym for FORmula TRANslation, a widely used high-level computer programming language developed in the USA from the 1950s onwards for mathematical, engineering, and scientific use.
| The Fortran Automatic Coding System for the IBM 704 (October 15, 1956), the first Programmer's Reference Manual for Fortran | |
| Paradigm: | multi-paradigm: procedural, imperative, structured, object-oriented |
|---|---|
| Appeared in: | 1957 |
| Designed by: | John W. IBM |
| Typing discipline: | strong, static |
| Major implementations: | GFortran, Open Watcom, XL Fortran, many others |
| Influenced: | ALGOL 58, PL/I |
Fortran (previously FORTRAN) is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing. Originally developed by IBM in the 1950s for scientific and engineering applications, Fortran came to dominate this area of programming early on and has been in continual use in computationally intensive areas such as climate modeling, computational fluid dynamics (CFD), computational physics, and computational chemistry for half a century.
Fortran (an acronym derived from The IBM Mathematical Formula Translating System) encompasses a lineage of versions, each of which evolved to add extensions to the language while retaining compatibility with previous versions. Successive versions have added support for processing of character-based data (FORTRAN 77), array programming, module-based programming and object-based programming (Fortran 90/95), and object-oriented and generic programming (Fortran 2003). The first manual for FORTRAN appeared in October 1956, with the first FORTRAN compiler delivered in April 1957. The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering.
By 1960, versions of FORTRAN were available for the IBM 709, 650, 1620, and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. For these reasons, FORTRAN is considered to be the first widely used programming language supported across a variety of computer architectures .
The development of FORTRAN paralleled the early evolution of compiler technology;
FORTRAN
The initial release of FORTRAN for the IBM 704 contained 32 statements, including:
DIMENSION and EQUIVALENCE statements Assignment statements Three-way arithmetic IF statement. and IF statements for manipulating sense switches and sense lights GOTO, computed GOTO, ASSIGN, and assigned GOTO DO loops Formatted I/O: FORMAT, READ, READ INPUT TAPE, WRITE, WRITE OUTPUT TAPE, PRINT, and PUNCH Unformatted I/O: READ TAPE, READ DRUM, WRITE TAPE, and WRITE DRUM Other I/O: END FILE, REWIND, and BACKSPACE PAUSE, STOP, and CONTINUE FREQUENCY statement (for providing optimization hints to the compiler)FORTRAN II
IBM's FORTRAN II appeared in 1958. Six new statements were introduced:
SUBROUTINE, FUNCTION, and END CALL and RETURN COMMONOver the next few years, FORTRAN II would also add support for the DOUBLE PRECISION and COMPLEX data types.
FORTRAN III
IBM also developed a FORTRAN III in 1958 that allowed for inline assembler code among other features; Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine.
FORTRAN IV
Starting in 1961, as a result of customer demands, IBM began development of a FORTRAN IV that removed the machine-dependent features of FORTRAN II (such as READ INPUT TAPE), while adding new features such as a LOGICAL data type, logical Boolean expressions and the logical IF statement as an alternative to the arithmetic IF statement. FORTRAN IV was eventually released in 1962, first for the IBM 7030 ("Stretch") computer, followed by versions for the IBM 7090 and 7094.
FORTRAN 66
Perhaps the most significant development in the early history of FORTRAN was the decision by the American Standards Association (now ANSI) to form a committee to develop an "American Standard Fortran." The resulting two standards, approved in March 1966, defined two languages, FORTRAN (based on FORTRAN IV, which had served as a de facto standard), and Basic FORTRAN (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard became known as FORTRAN 66 (although many continued to refer to it as FORTRAN IV, the language upon which the standard was largely based). FORTRAN 66 effectively became the first "industry-standard" version of FORTRAN. FORTRAN 66 included:
Main program, SUBROUTINE, FUNCTION, and BLOCK DATA program units INTEGER, REAL, DOUBLE PRECISION, COMPLEX, and LOGICAL data types COMMON, DIMENSION, and EQUIVALENCE statements DATA statement for specifying initial values Intrinsic and EXTERNAL (e.g., library) functions Assignment statement GOTO, assigned GOTO, and computed GOTO statements Logical IF and arithmetic (three-way) IF statements DO loops READ, WRITE, BACKSPACE, REWIND, and ENDFILE statements for sequential I/O FORMAT statement CALL, RETURN, PAUSE, and STOP statements Hollerith constants in DATA and FORMAT statements, and as actual arguments to procedures Identifiers of up to six characters in length Comment linesFORTRAN 77
After the release of the FORTRAN 66 standard, compiler vendors introduced a number of extensions to "Standard Fortran", prompting ANSI in 1969 to begin work on revising the 1966 standard. Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. The new standard, known as FORTRAN 77, added a number of significant features to address many of the shortcomings of FORTRAN 66:
CHARACTER data type, with vastly expanded facilities for character input and output and processing of character-based data IMPLICIT statement Block IF statement, with optional ELSE and ELSE IF clauses, to provide improved language support for structured programming OPEN, CLOSE, and INQUIRE statements for improved I/O capability Direct-access file I/O PARAMETER statement for specifying constants SAVE statement for persistent local variables Generic names for intrinsic functionsAn important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978. Department of Defense, standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. These features would eventually be incorporated into the Fortran 90 standard.
The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect.
Fortran 90
The much delayed successor to FORTRAN 77, informally known as Fortran 90, was finally released as an ANSI Standard in 1992. This major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard:
Free-form source input, also with lowercase Fortran keywords Modules, to group related procedures and data together, and make them available to other program units, including the capability
to limit the accesibility to only specific parts of the module.
Fortran 95
Fortran 95 was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification:
FOR ALL and nested WHERE constructs to aid vectorization User-defined PURE and ELEMENTAL proceduresAn important supplement to Fortran 95 was the ISO technical report TR-15581: Enhanced Data Type Facilities, and informally known as the Allocatable TR. This specification defined enhanced use of ALLOCATABLE arrays, prior to the availability of fully Fortran 2003-compliant Fortran compilers. In addition, aliasing is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.)
Fortran 2003
The most recent standard, Fortran 2003, is a major revision introducing many new features. A comprehensive summary of the new features of Fortran 2003 is available at the ISO Fortran Working Group (WG5) official Web site, and may be downloaded directly as a PDF file or gzipped PostScript file.
Fortran 2008
Efforts are underway to develop a revision to Fortran 2003, tentatively called Fortran 2008. As with Fortran 95, this is intended to be a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing a select few new capabilities. Proposed new capabilities include
Co-array Fortran – a parallel processing model BIT data typeA full list is in the report "The language features that have been chosen for Fortran 2008" PDF file.
The legacy of FORTRAN
Since Fortran has been around for nearly fifty years, there is a vast body of Fortran in daily use throughout the scientific and engineering communities. Indeed, one finds that even today, half a century later, floating-point benchmarks to gauge the performance of new computer processors are still written in Fortran (e.g., CFP2000, the floating-point component of the SPEC CPU2000 benchmarks), an eloquent tribute to the longstanding floating-point high performance of the language.
Language features
The Fortran language features described are intended to be a fairly comprehensive overview of the Fortran language;
It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor.
Variants of Fortran
Specific variants
Vendors of high-performance scientific computers (e.g., Burroughs, CDC, Cray, Honeywell, IBM, Texas Instruments, and UNIVAC) added extensions to Fortran to take advantage of special hardware features such as instruction cache, CPU pipelines, and vector arrays. For example, one of IBM's Fortran compilers (H Extended IUP) had a level of optimization which reordered the machine language instructions to keep multiple internal arithmetic units busy simultaneously.
Object-Oriented Fortran is an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel.
Fortran-based languages
Prior to FORTRAN 77, a number of preprocessors were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. (Ratfor and Ratfiv, for example, implemented a remarkably C-like language, outputting preprocessed code in standard FORTRAN 66.)
The Fortran-95 Standard includes an optional Part 3 which defines an optional conditional compilation capability.
Many Fortran compilers have integrated subsets of the C preprocessor into their systems.
SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems.
F was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the EQUIVALENCE statement.
Criticisms and rebuttals
Arcane syntax
As what was essentially a first attempt at designing a high-level language, Fortran's syntax is sometimes regarded as archaic by programmers familiar with subsequently developed languages such as C.
Early FORTRAN syntax (prior to Fortran 90) did not in general treat blanks as significant, which made writing robust and efficient lexical analyzers for Fortran very difficult.
A language tailored to "specialists"
Historical versions of Fortran could rightly be criticized for arbitrary conventions such as implicit typing and fixed-form source input, which together with a paucity of block structures could allow careless or obfuscated programming practices. Fortran 95 provides concise statements for applying mathematical operations directly to entire arrays, which not only improves program readability but also assists the compiler in vectorizing operations. As another example, from its earliest days Fortran provided full support for complex numbers (used, e.g., in the computation of Fourier transforms and in power engineering calculations), a feature not supported by ANSI C until the advent of the ISO/IEC 9899:1999 ("C99") standard.
For these reasons, while Fortran is seldom used outside of scientific and engineering numerical work, it remains the language of choice for high-performance numerical computing.
C/C++ is 'just as fast'
Fortran was designed to create fast executable code for scientific programming. Few other languages treat arrays, especially multi-dimensional arrays, as cleanly and simply as Fortran does.
In particular, Fortran data items are not allowed to alias one another, except in very well-defined and explicit situations. This assists Fortran compilers in generating very efficient code, by default, compared to pointer-intensive languages.
Fortran 95 is slower than FORTRAN 77
Most programs in FORTRAN 77 are valid in Fortran 95, or require only minor changes. Any observed slowdown resulting from rewriting a FORTRAN 77 program in Fortran 95 is usually caused by improper usage of Fortran 95 features.
Fortran programs require static storage allocation
It is a common misconception that Fortran requires static storage allocation for all local variables. Both the FORTRAN 66 and FORTRAN 77 Standards allowed, but did not require, a fully static implementation. FORTRAN 77 introduced the SAVE statement to allow a programmer to state explicitly which variables are required to retain their values when they go out of scope.
Code examples
The sample programs can be compiled and run with any standard Fortran compiler (see the end of this article for lists of compilers). Most modern Fortran compilers expect a file with a .f or .for extension (for FORTRAN 66 or FORTRAN 77 fixed-form source, although the FORTRAN 66 dialect may have to be selected specifically with a command-line option) or .f90/.f95 extension (for Fortran 90/95 free-form source, respectively).
FORTRAN jokes
For a programming language with a half-century legacy, FORTRAN not surprisingly has accumulated its share of jokes and folklore.
Standard jokes
"GOD is REAL unless declared INTEGER." Joke, circa 1980 (following the standardization of FORTRAN 77): "Q: What will the scientific programming language of the year 2000 look like? A: Nobody knows, but its name will be FORTRAN." A good FORTRAN programmer can write FORTRAN code in any language.From the historical record
FORTRAN, the infantile disorder, by now nearly 20 years old, is hopelessly inadequate for whatever computer application you have in mind today: it is now too clumsy, too risky, and too expensive to use. Edsger W. D., and lasted until about 1957, when FORTRAN abandoned the practice." —Sun FORTRAN Reference Manual "People are very flexible and learn to adjust to strange surroundings — they can become accustomed to read Lisp and Fortran programs, for example." —Art of PROLOG, Leon Sterling and Ehud Shapiro, MIT Press "Warning: Go directly to Jail. USA Standard FORTRAN, informally known as FORTRAN 66, American National Standards Institute. American National Standard – Programming Language FORTRAN, also known as ISO 1539-1980, informally known as FORTRAN 77, American National Standards Institute. American National Standard – Programming Language Fortran Extended, informally known as Fortran 90, American National Standards Institute. Information technology – Programming languages – Fortran – Part 1: Base language, informally known as Fortran 95. Information technology – Programming languages – Fortran – Part 1: Base language, informally known as Fortran 2003. "Draft standard industrial real-time FORTRAN". POSIX FORTRAN 77 Language Interface – Part 1: Binding for System Application Program Interface [API].History
"The FORTRAN Automatic Coding System" by Backus, et al., Proceedings of the WJCC (Western Joint Computer Conference), Los Angeles, California, February, 1957.describes the design and implementation of the first FORTRAN compiler by the IBM team. Historic Documents in Computer Science — Early Fortran manuals The FORTRAN Automatic Coding System for the IBM 704 EDPM (PDF file) — The very first Fortran manual, by John Backus et al. and dated "15 October 1956" (Attests to the origin of the name FORTRAN as deriving from The IBM Mathematical Formula Translating System. And note that the front cover page refers to the language as Fortran, not FORTRAN.) History of FORTRAN and FORTRAN II at the Computer History Museum John Backus (August 1978). History of programming languages FORTRAN at HOPL site "The IBM CE Manual for FORTRAN I, II, and 709", from 1959 Systems Manual for 704 FORTRAN and 709 FORTRAN - IBM, April, 1960. It also spells FORTRAN, the acronym, in the text itself, as "Fortran".
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