Re: limitations on optimizers for conditional compilation

[munck@linus.UUCP (Robert Munck)]

In article <8912110202.AA11909@mbunix.mitre.org> emery@MBUNIX.MITRE.ORG (Emery) writes:
>... (discusses conditional compiliation of executable code)...   
>
>Where this approach fails, though, is in non-statements such as type
>declarations.  It would be nice to have support for this:
>	  record
>#ifdef VAX
>	    y : float_64;
>#elsif IBM_PC_WITH_8087
>	    y : IEEE_float;
>#endif
>
>... but I also suspect that it wouldn't take much to come up
>with type definitions where a variant record approach wouldn't work.

I'm not so sure about this anymore.  I have a feeling that "type
definitions where a variant record approach wouldn't work" may well be
the equivalent of "programs where structured coding doesn't work."

We oldtimers are all used to playing fast and loose with the source text
with preprocessor statements, including such horrors as "manufacturing"
keywords from conditionals and compile-time variables.  Maybe, just
maybe, that isn't such a good idea, and the good software engineering
practice would be to stick to the language definition, variant records
and all.

I have only one data-point, a small OS with a fair number of "sysgen"
variables and choices.  I found it fairly easy and "satisfactory to my
esthetic sense" to do everything entirely within the language.