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Forum:	      Compiler


References: COMPILE (p438), COMPILE-FILE (p439)

Category: ADDITION

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

Problem Description:

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:

:OVERRIDE boolean

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

innermost call.

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.

Test Case:





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.

Current Practice:

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.

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