On extending Fortran control structures to facilitate structured programming

Abstract

A number of preprocessors and other extensions of Fortran have been implemented recently, aimed at adding "disciplined" control structures to the language. In spite of wide variations in the details of these dialects, many common features can be perceived. This paper attempts to identify these common features, and to draw some conclusions concerning their relation to a possible future widely acceptable structured Fortran language.Several different kinds of altarnative and lterative structures are described, along with some of the ways they have been implemented. The use of internal procedures for top-down refinement is noted. Few, of the dialects include a general multiple level exit, although in principle thls feature is needed for structured programming. Use of labels seems to be preferable to any alternative way of implementing, this feature in Fortran.Because of the importance of compatibility with existing programs, and for other reasons, it is unlikely that the GO TO staterent will disappear from Fortran in the forseeable future. However. with the addition of new control structures it should be possible to develop processors that warn againtst certain particularly awkward usages of GO TO statements.Further efforts are recommended, including continued support of the ANSI X3J3 Fortran standards committee, and the establishment of a separate group charged with oredicting trends and making timely recommendations for future extensions to the language.