Issue DISASSEMBLE-SIDE-EFFECT Writeup

Issue:         DISASSEMBLE-SIDE-EFFECT

References:    DISASSEMBLE (p. 439), COMPILE (p. 439)

Category:      CLARIFICATION

Edit history:  Version 2 by Pierson 12/30/87

               Version 3 by Pierson  1/21/88

	       Version 4 by Pierson  6/10/88 correct VAX Lisp practice

Status:        Ready For Release?


Problem description:


The definition of DISASSEMBLE says that "if the relevant function is

not a compiled function, it is first compiled.".  The definition of

COMPILE says that "If name is a non-nil symbol, then the

compiled-function is installed as the global function definition of

the symbol...".  Several implementations have taken this to mean that

if DISASSEMBLE is passed a symbol which has an uncompiled function

definition, then it has the side-effect of (COMPILE 'symbol).


Proposal (DISASSEMBLE-SIDE-EFFECT:DO-NOT-INSTALL):


Clarify that when DISASSEMBLE compiles a function, it will never

install the newly compiled function.


Test Cases/Examples:


    (DEFUN F (A) (1+ A))

    (EQ (SYMBOL-FUNCTION 'F)

	(PROGN (DISASSEMBLE 'F)

	       (SYMBOL-FUNCTION 'F)))


This code will return T if this proposal is adopted.  Some current

implementations will return T, some will return NIL.


Rationale:


Several current implementations of DISASSEMBLE have surprising side

effects, especially for new users.


Current practice:


Allegro CL installs the compiled definition.  Lucid, Symbolics, Xerox,

VAX Lisp, and KCL don't install it.


Cost to Implementors:


Some implementations will have to make a simple change.


Cost to Users:


Very little.  DISASSEMBLE is really part of the environment and is

probably not called by much, if any user code.


Cost of non-Adoption:


DISASSEMBLE will continue to surprise less experienced users.


Benefits:


DISASSEMBLE will become the predictable debugging function it was

meant to be.


Aesthetics:


Some who worried that DISASSEMBLE was supposed to install the compiled

function may find that the language has become a little cleaner.


Discussion:


DISASSEMBLE is an environment feature; some question has been raised

as to the place and force of environment features in the standard.

However, this proposal stands if DISASSEMBLE is part of the standard

language.