A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
In computer science, a preprocessor is a program that processes its input data to produce output that is used as input to another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers...
for Fortran 66. It provided modern control structures, unavailable in Fortran 66, to replace GOTO
Goto
goto is a statement found in many computer programming languages. It is a combination of the English words go and to. It performs a one-way transfer of control to another line of code; in contrast a function call normally returns control...
s and statement numbers.
Features
Ratfor provides the following kinds of flow-control statements, described by Kernighan and Plauger as "shamelessly stolen from the language C, developed for the UNIX operating system by D.M. Ritchie
Dennis Ritchie
Dennis MacAlistair Ritchie , was an American computer scientist who "helped shape the digital era." He created the C programming language and, with long-time colleague Ken Thompson, the UNIX operating system...
" ("Software Tools", p. 318):
statement grouping with braces
if-else, while, for, do, repeat-until, break, next
"free-form" statements, i.e., not constrained by Fortran format rules
<, >, >=, ... in place of .LT., .GT., .GE., ...
include
# comments
For example, the following code
if (a > b) {
max = a
} else {
max = b
}
might be translated as
IF(.NOT.(A.GT.B))GOTO 1
MAX = A
GOTO 2
1 CONTINUE
MAX = B
2 CONTINUE
The version of Ratfor in Software Tools is itself written in Ratfor, as are the sample programs, and inasmuch as its own translation to Fortran is available, it can be ported to any Fortran system. Ratfor source code file names end in .r or .rat.
It basically took the flow control statements and generated regular fortran which then could be compiled. It allowed you to use structured programming in writing the code.
Brian Wilson Kernighan is a Canadian computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed to the development of Unix. He is also coauthor of the AWK and AMPL programming languages. The 'K' of K&R C and the 'K' in AWK both stand for...
at Bell Telephone Laboratories in 1974, and described in Software-Practice & Experience in 1975. It was used in the book "Software Tools" (Kernighan
Brian Kernighan
Brian Wilson Kernighan is a Canadian computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed to the development of Unix. He is also coauthor of the AWK and AMPL programming languages. The 'K' of K&R C and the 'K' in AWK both stand for...
Purdue University, located in West Lafayette, Indiana, U.S., is the flagship university of the six-campus Purdue University system. Purdue was founded on May 6, 1869, as a land-grant university when the Indiana General Assembly, taking advantage of the Morrill Act, accepted a donation of land and...
, an improved version of the ratfor preprocessor was written. It was called Mouse4, as it was smaller and faster than ratfor. A published document by Dr. Douglas Comer
Douglas Comer
Douglas Earl Comer is a writer and professor best known for his work in the early development of the Internet.- Education and career :...
, professor at Purdue concluded "contrary to the evidence exhibited by the designer of Ratfor, sequential search is often inadequate for production software. Furthermore, in the case of lexical analysis, well-known techniques do seem to offer efficiency while retaining the simplicity, ease of coding and modularity of ad hoc methods." (CSD-TR236).
In comparison of the ratfor preprocessor on a program of 3000 source lines running on a CDC 6500 system took 185.470 CPU seconds. That was cut by 50% when binary search was used in the ratfor code. However rewriting the ad hoc lexical scanner using a standard method based on finite automata took the program to 12.723 seconds.
