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Issue WITH-COMPILATION-UNIT (Version 4)
- To: CL-Compiler@SAIL.Stanford.EDU
- Subject: Issue WITH-COMPILATION-UNIT (Version 4)
- From: Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>
- Date: Mon, 10 Apr 89 18:35 EDT
v3 passed 11-6 with an amendment to say it defers "warnings" rather than
"actions" and with an amendment to say it does not apply to the COMPILE
function (only to COMPILE-FILE). I had to make this new version for my
records to reflect that one-word change. -kmp
References: COMPILE (p438), COMPILE-FILE (p439)
Edit history: 29-Sep-88, Version 1 by Pitman
10-Mar-89, Version 2 by Pitman (merge comments)
13-Mar-89, Version 3 by Loosemore (update discussion)
10-Apr-89, Version 4 by Pitman (wording change per X3J13)
Status: Ready for release
Some actions done by the compiler (and particularly the file compiler)
are typically deferred until the "very end" of compilation. For example,
some compilers complain about "functions seen but not defined".
Unfortunately, since COMPILE-FILE is the largest unit of granularity,
and since systems often extend over more than one file, it often happens
that the compiler needlessly complains at the end of compiling one file
about the absence of functions defined in the next file.
Add the following new macro:
WITH-COMPILATION-UNIT options &BODY forms [Macro]
Executes forms from left to right. Within the dynamic context
of this form, warnings deferred by the compiler until "the end of
compilation" will be deferred until the end of the outermost call
to WITH-COMPILATION-UNIT. The result(s) are the same as that of
the last of the FORMS (or NIL if FORMS is null).
OPTIONS is a keyword/value list, where only the values are
evaluated. The set of keywords permitted may be extended by the
implementation, but the only keyword defined by this standard is:
The default is NIL. If nested dynamically only the outer call
to WITH-COMPILATION-UNIT has any effect unless BOOLEAN is T,
in which case warnings are deferred only to the end of the
It follows that the functions COMPILE and COMPILE-FILE should
provide the effect of (WITH-COMPILATION-UNIT (:OVERRIDE NIL) ...)
around their code.
Any implementation-dependent extensions may only be provided
as the result of an explicit programmer request by use of
an implementation-dependent keyword. Implementations are forbidden
from attaching additional meaning to a conforming use of this
Note also that not all warnings are deferred. In some implementations,
it may be that none are deferred. This proposal only creates an
interface to the capability where it exists, it does not require the
creation of the capability. An implementation which does not do
deferred warnings may correctly implement this as expanding into PROGN.
(DEFUN COMPILE-FILES (&REST FILES)
(MAPCAR #'(LAMBDA (FILE) (COMPILE-FILE FILE)) FILES)))
(COMPILE-FILES "A" "B" "C")
processes deferred warnings only after compiling all of A, B, and C.
This will make the development of portable system-construction tools
considerably more convenient.
Lucid has a very similar facility, called WITH-DEFERRED-WARNINGS.
TI Explorer and Symbolics Genera have a similar facility, which they
Cost to Implementors:
In implementations which have no deferred warnings, there is no cost.
In implementations which have deferred warnings, the cost is probably
fairly small -- usually just a matter of writing interfacing the
proposed macro to an existing one.
Cost to Users:
None. This is a compatible addition.
Cost of Non-Adoption:
Portable system-construction tools would continue to print lots of
spurious warnings because they would have no way to tell the system
that a set of files was working together.
The cost of non-adoption is avoided.
The ability to create a compilation unit other than a file is important.
Pitman and Benson support this addition.
One could imagine adding more options at a later date.
It was the opinion of the compiler committee that there was room for
expansion here to address issues like bounding the scope of global
proclamations, sharing compile-time environments across files, etc.
However, insufficient work was done on this to justify putting such
a thing into the standard. The only clear need we have at this time
was to defer warnings, but we chose a general name like
WITH-COMPILATION-UNIT rather than a specific name like Lucid's
WITH-DEFERRED-WARNINGS in order to encourage implementations to
experiment with other kinds of options under implementation-specific
keywords. Perhaps by the time of the next standard there will be
sufficient understanding of this area to warrant further elaboration
of this primitive.
Kim Barrett says:
I strongly oppose the behavior you proposed for compile and
compile-file. It is my belief that whether to override or not must be
controlled through an argument to the compile functions, with the
default being to override. Otherwise, all existing code which makes
use of the compile functions must be modified to protect itself by
wrapping a (with-compilation-unit (:override t) ...) around the calls
to the compiler.
Consider a stream system built on an object system which will compose
and compile functions on the fly on an as needed basis. It would be
very strange for the functions so generated while doing file io for
the user's compile-file to have any relationship with said
I agree with your position that implementation-dependent extensions
must be explicitly requested.