.
In some cases the line below the message may differ slightly from the corresponding string of symbols above; for example, an identifier might be rendered by Ident. It is possible for a single syntactical error to cause more than one diagnostic.
A few syntactical errors are corrected by the compiler, and a message is put out to this effect. An example is a semicolon immediately preceding else.
According to the comment conventions of Algol, any string of symbols following end and not containing end, else or a semicolon is treated as comment. As a result, the omission of one of these symbols following end does not always cause an error in compilation but will cause a portion of the program to be skipped over by the compiler. Thus for example, in
... x := a + b end for i := 1 step 1 ...
the FOR statement will be skipped at least in part. The compiler will put out a caution message in this and some other cases, but it will not change the program.
If an identifier is not declared (or possibly declared in the wrong place), a message is put out below the program listing together with the undeclared identifier.
The compiler does not check the type of identifiers. Therefore, such errors as a Boolean variable in an arithmetic expression, or the brackets of a subscripted variable replaced by parentheses, are not detected, and an incorrect program may be compiled.
VIII. Running Programs
The Algol program is punched on cards in the hardware representation described in [Appendix B]. The format is essentially free field: spaces have no significance except within escape symbols and string quotes. Only the first 72 columns, however, are interpreted by the compiler. The remaining columns may be used for identification purposes. Care must be taken when a string is continued onto the next card, as the continuation will begin in column 1. The program listing will have the same format as the cards.