Issue COMPILER-VERBOSITY Writeup

Forum:	    	Compiler

Issue:		COMPILER-VERBOSITY

References:	CLtL p. 438-329; 426

		issue COMPILER-DIAGNOSTICS

Category:	ENHANCEMENT

Edit History:   V1, 25 Oct 1988, Sandra Loosemore

    	    	V2, 12 Dec 1988, Dan L. Pierson (add USE-CONDITIONS)

    	    	V3, 15 Dec 1988, Dan L. Pierson (expand on conditions)

    	    	V4, 21 Dec 1988, Dan L. Pierson (reword and clarify)

		V5, 06 Jan 1989, Sandra Loosemore (update discussion)

		V6, 26 Jan 1989, Sandra Loosemore (remove USE-CONDITIONS)

Status:		Ready for release



Problem Description:


Implementations vary widely in the amount of information that is printed

out by COMPILE-FILE.  In some situations, it would be useful to control

how much information is printed.



Proposal COMPILER-VERBOSITY:LIKE-LOAD:


Introduce special variables, *COMPILE-VERBOSE* and *COMPILE-PRINT*,

with implementation-dependent initial values.


Add :VERBOSE and :PRINT keyword arguments to the function

COMPILE-FILE, analogous to those for the function LOAD.


The :VERBOSE argument (which defaults to the value of

*COMPILE-VERBOSE*), if true, permits COMPILE-FILE to print a message

in the form of a comment to *STANDARD-OUTPUT* indicating what file is

being compiled and other useful information.


The :PRINT argument (which defaults to the value of *COMPILE-PRINT*),

if true, causes information about top-level forms in the file being

compiled to be printed to *STANDARD-OUTPUT*.  Exactly what is printed

will vary from implementation to implementation, but nevertheless some

information will be printed.


Introduce a special variable *LOAD-PRINT*, which has an initial value of

NIL.  State that the default value of the :PRINT argument to LOAD is

*LOAD-PRINT* (rather than NIL).



Rationale:


This proposal makes COMPILE-FILE behave like LOAD.  There is already

some precedent for doing this (for example, issue COMPILE-FILE-PACKAGE,

which makes COMPILE-FILE as well as LOAD rebind *PACKAGE*).


Adding the *LOAD-PRINT* variable allows the printing of messages by

LOAD to be controlled either on a global or a per-call basis.



Current Practice:


COMPILE-FILE prints out progress messages in nearly all

implementations.


Lucid provides a :MESSAGES keyword argument to COMPILE-FILE, which can

either be a stream to send messages to, or NIL to suppress messages.

The default value is T, which sends messages to "the standard terminal

device".


On the TI Explorer, COMPILE-FILE displays the name of the function

being compiled when the option :VERBOSE T is given or special variable

COMPILER:COMPILER-VERBOSE is true.  (In other words, they use :VERBOSE

to mean what this proposal says to use :PRINT for.)


Symbolics Cloe already has a *LOAD-PRINT* variable.



Cost to implementors:


This is an incompatible change for some implementations.  While the

changes required should be conceptually simple, their implementation

may involve a significant amount of grunt work.  At least two

implementations already provide some similar mechanism for suppressing

messages.



Cost to users:


Some (non-portable) user code may break in implementations where this

is an incompatible change.


No user code should be broken by the addition of the *LOAD-PRINT*

variable, since the default behavior for the :PRINT keyword to LOAD 

is unchanged.



Benefits:


Users are given a portable way to control how much information is printed

by COMPILE-FILE.



Discussion:


This issue addresses an extension to the language.  If this proposal

is not accepted, the standard will simply continue not to say anything

about whether COMPILE-FILE can print progress messages, or what stream

such messages are directed to.