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(The following information augments or overrides the information in Section 1.4 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 1 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)
The definition of the GNU Fortran language is akin to that of the ANSI FORTRAN 77 language in that it does not generally require conforming implementations to diagnose cases where programs do not conform to the language.
g77 as a compiler is being developed in a way that
is intended to enable it to diagnose such cases in an easy-to-understand
A program that conforms to the GNU Fortran language should, when
compiled, linked, and executed using a properly installed
system, perform as described by the GNU Fortran language definition.
Reasons for different behavior include, among others:
Despite these "loopholes", the availability of a clear specification
of the language of programs submitted to
g77, as this document
is intended to provide, is considered an important aspect of providing
a robust, clean, predictable Fortran implementation.
The definition of the GNU Fortran language, while having no special
legal status, can therefore be viewed as a sort of contract, or agreement.
This agreement says, in essence, "if you write a program in this language,
and run it in an environment (such as a
g77 system) that supports
this language, the program should behave in a largely predictable way".