Issue COMPILER-WARNING-STREAM Writeup

Status: passed, June 87

Issue:        COMPILER-WARNING-STREAM

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

Category:     CLARIFICATION/CHANGE

Edit history: Version 1 by Pitman 02/27/87

              Version 2 at committee meeting 15-Mar-87

              Version 3 Masinter 15-Mar-87

              Version 4 by Fahlman, incorporate Dribble

              Version 5 by Masinter, 29-May-87, revert to Version 3

              Version 6 by Masinter,  5-Jun-87, minor formatting

              


Problem Description:


 The description of the COMPILE and COMPILE-FILE functions does not

 explicitly permit them to print warnings. If this is to be allowed, it

 should be an explicitly expressed part of the contract.


Proposal (COMPILER-WARNING-STREAM:ERROR-OUTPUT)


 COMPILE and COMPILE-FILE are permitted to output warnings; warnings

 should go to the stream that is the value of *ERROR-OUTPUT*.


Rationale:


 Compiler warning output is a widely accepted extension to the

 compilation. Warnings that come via the WARN function will go to the

 stream that is the value of *ERROR-OUTPUT*.


Current Practice:


 Some implementations send compiler warning output to *ERROR-OUTPUT*.

 Other implementations send it to *STANDARD-OUTPUT*.


Adoption Cost:


 In most cases, the change to the compiler to redirect output is expected to be very slight.


Benefits:


 Currently, it is difficult to redirect the output of COMPILE and

 COMPILE-FILE because it isn't clear where it's directed.


Conversion Cost:


 Most user programs that care are probably already tolerant of both

 situations or naively expect that output will go to *ERROR-OUTPUT*. As

 such, most users will probably perceive this as a clarification.


Aesthetics:


 Most users will probably perceive this change as a simplification

 because it will allow the kind of warning that comes from WARN and the

 kind of warning that comes from compilation to be conceptually grouped.


Discussion:


 This was a problem in adapting MACSYMA to Common Lisp because Macsyma

 provides alternate user interfaces to the compiler which it needs to be

 able to control.


 The committee considered extending the proposal to describe the

 interaction with DRIBBLE on the warning output, but found that DRIBBLE

 was so underspecified as to make the task impossible. DRIBBLE should be

 considered in a separate proposal.


 The cleanup committee supports this change as stated.