5.4.4 ‘@a’: Begin code part of unnamed section, and mark

‘@a’ begins the code part of an unnamed section (just as does ‘@A’), and in addition marks the next unreserved identifier it finds as defined in this section. Precisely,

‘@a’ == ‘@A@[’

Originally, FWEB did not contain the ‘@A’ command, so when the functionality of automatically marking the next unreserved identifier (see AT[) was added, it was natural to add it to ‘@a’. A reasonable style of coding is to always use ‘@a’ if you don’t know any better; if you sometime run into trouble, you can then change selected ‘@a’s to ‘@A’s. For example, it is appropriate to use ‘@a’ if one codes one function per section. E.g.,

@c
@ 
@a
int
subrtn()
{}

Here the ‘@a’ marks ‘subrtn’ as defined in this section; if that identifier is used elsewhere, it will be subscripted with the section number. (To turn this feature off, use ‘-f’; see -f.) However, if a section contains an arbitrary code fragment, the code part should probably begin with ‘@A’. E.g.,

@c
@
@A
x = y;

If one had used ‘@a’ here, the x would have been marked as defined here, which is not what one wants.