Part 3

A few features of the language have been subject to more than one interpretation. Fortunately, the vast majority of programs will not involve these ambiguities, but for the few that do it will be necessary to know what decisions the compiler makes. This appendix indicates these decisions for the more controversial areas.

1. Side effects in function designators. The evaluation of primaries in expressions is not strictly left to right allowing for precedence rules. In particular, the value of a variable in an expression is never stored in a temporary simply to preserve its value from change by the evaluation of a function designator in the expression. Otherwise, the evaluation does proceed from left to right and according to precedence rules, including the referencing of formal parameters and the calculation of the address of subscripted variables. All function designators are evaluated in Boolean expressions.

2. Own variables and arrays in procedures. The own quantities local to the body of a procedure which is called from more than one point in a program record the history of the procedure as opposed to a history of each point of reference. In other words, only one copy of the own quantities is preserved.

APPENDIX G Fortran Subprograms in an Algol Program

The standard procedures FORTRAN, FORTRANF, FTN, and FTNF are used to call compiled Fortran subroutines and functions from within an Algol program. Each procedure has one parameter which is a call of the desired Fortran subprogram. The Fortran subprogram must be declared external as described in Section V.

The use of these procedures simply causes a Fortran calling sequence to be generated by the compiler. Of course the subprogram could be written in CODAP as well as Fortran, provided it is designed to link through a Fortran-type calling sequence.

The procedures are used as follows:

FORTRAN—generates a Fortran 62 calling sequence for a subroutine FORTRANF—generates a Fortran 62 calling sequence for a function FTN—generates a Fortran 63 calling sequence for a subroutine FTNF—generates a Fortran 63 calling sequence for a function

Each of these procedures is standard, i.e., available without declaration. FORTRANF and FTNF are used in expressions.

Examples:

x := FTNF (ALPHA(T,A[0,0]))

FORTRAN (SUB(I + J)) .

The following restrictions must be observed: labels, procedures with no parameters, standard procedure names, and array names cannot be used as arguments of a call of a Fortran subprogram. However, in the case of an array, the subscripted variable which is the first element of the array will satisfy a Fortran subroutine which has an array name as a formal parameter. The name of the Fortran subprogram cannot be a formal parameter. Literals must be enclosed in string quotes.

Footnotes

[1]See Appendix A for syntactical definition.

[2]For definition of Fortran format, see Control Data Fortran-62 Reference Manual.

Acknowledgment

The author was greatly assisted in the preparation of this document by several persons who have contributed labors or advice to the construction of the compiler. These include N. B. Alexander and A. A. Grau, also K. A. Wolf of Control Data Corporation, and especially R. G. Stueland of Control Data Corporation.

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Transcriber’s Notes

In the HTML version, represented code in a monospaced font, with keywords in boldface as in the Revised Report. Corrected a few palpable typos. Created an original cover image, using elements from the printed book, for free and unrestricted use with this eBook.