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Status:       Accepted v8 (superseding v7) on 15-0 vote, Jun-90


References: LISP, USER, SYSTEM packages (p181)





Edit history: 07-Jul-88, Version 1 by Pitman

23-Sep-88, Version 2 by Masinter

5-Oct-88, Version 3 by Masinter

7-Oct-88, Version 4 by Masinter (response to KMP)

8-Dec-88, Version 5 by Masinter

(add property lists)

12-Dec-88, Version 6 by Masinter (respond to comments)

17-Mar-89, Version 7 by Masinter (as amended Jan 89 X3J13)

3-Jan-90, Version 8 by Barrett (add more cases)

Problem Description:

CLtL specifies that

``The package named LISP contains the primitives of

the Common Lisp system. Its external symbols include

all of the user-visible functions and global variables

that are present in the Common Lisp system, such as

CAR, CDR, *PACKAGE*, etc. Almost all other packages will

want to use LISP so that these symbosl will be accessible

without qualification.''

It specifies "all" but not "all and only".

Some implementations place their extensions in the Lisp package.

Nothing in CLtL explicitly prohibits this, but it leads to problems

in general. For example:

- A user defining a function by a name not mentioned in CLtL may be

surprised to clobber a system function in some implementations

- In one particular implementation, the variable HELP was a system

constant, so that ((LAMBDA (HELP) ...HELP...) "Press ? for help.")

signalled a correctable error (asking what variable to bind

instead of HELP :-).


Specify that, not only must the LISP package contain at least all of the

symbols listed in the standard, it will have no other external symbols.

(The LISP package may have additional internal symbols.)

External symbols of the LISP package may have function, macro, or special

form definitions, setf method definition, top level value or SPECIAL

proclamations, or type definitions only if explicitly permitted in the

specification. That is, a program is valid Common Lisp if it assumes that

this is true; for example, FBOUNDP will be false for all external symbols of

the LISP package except those documented to be functions, macros or special

forms; no setf method will be defined for such a symbol, and FBOUNDP on

(SETF symbol) will be false; BOUNDP will be false for all those except those

documented to be variables, and portable programs can use symbols in the

LISP package as local lexical variables with the presumption that the

variables are not proclaimed special, except for those variables specified

as constants or variables.

No external symbols of the LISP package may have properties with

property indicators that are either external symbols of packages

defined in the standard or are otherwise accessible in the USER


This proposal constrains implementations as to what their

initial package configuration must be. That is, valid programs

can assume that the conformal Lisp implementation will not

have prohibited properties. The proposal LISP-SYMBOL-REDEFINITION

addresses the converse; that is, what user programs are allowed

to do.

Eliminate the requirement that the initial Common Lisp system

have a package named "SYSTEM". Specify that implementations may

have several other packages available, that these should be

documented. If it is appropriate, the standard might contain

as an example that implementations might have a package named


Clarify that the "USER" package may have additional symbols interned

within it and that it may :USE other implementation-specific packages.


#1: The symbol HELP may not be on the LISP package because it is not

mentioned in CLtL.

#2: The symbol VARIABLE is specified to be on the LISP package (because

it is a valid second argument to the DOCUMENTATION function). Since

it is not defined as a variable, type, or function, however, it will

not initially be bound, defined as a type, or defined as a function,

macro or special form.


If extra symbols are permitted in the LISP package, users may be surprised

by relationships between the LISP package and other packages which they

did not expect, or may be surprised by functionality that they did not

expect. The degenerate case is:









Given such an implementation, even things like (LAMBDA (X) X) are not

valid because they attempt to bind "system constants". It is necessary

that the programmer be able to know for sure that an arbitrary name is

"free for use" and best way to conveniently assure this is to require

that the LISP package be unadulterated.

As for the additional definitions, there are situations where additional

definitions would cause a problem. For example, if a symbol on the Lisp

package were declared as a special variable even though that value was

not mentioned in the standard, that variable would behave incorrectly when

used as a lexical variable. Similarly, if a symbol in the lisp package

were defined as an implementation-dependent special form, problems might

result if a user redefined or even bound (as by FLET or MACROLET) that


The LISP package is the foothold from which portable programs establish

their desired environment. Careful control is desirable to make sure

everyone is starting off on the right foot.

Current Practice:

Some implementations have been known to add additional symbols (usually

functional and/or variable extensions) to the LISP package.

Several implementations have restricted the LISP package to only contain

those symbols in CLtL. (The exact set was difficult to extract because not all

LISP package symbols appeared in the index of CLtL.)

Even in those implementations that have only the prescribed symbols in CLtL,

there can be extra definitions for those symbols. For example, in Symbolics Genera,


are spuriously defined as special variables, and the symbol LAMBDA is defined

as a macro.

Performance Impact:


Cost to Implementors:

The actual cost of moving the symbols out of the LISP package in cases

where they are not already gone is quite small. However, if any

implementation really has to do this, it may have a number of suppositions

about what is in what package, and the changes could potentially be extensive.

Cost to Users:

This change is upward compatible with any portable program, but users

of a particular implementation's extensions may be forced to find their

functions in a different package, so there may be a measurable practical


In many cases where an extension symbol FOO is simply expected to have

been directly available (due to :USE "LISP"), it will work to just just

do (IMPORT 'new-home-package-for-foo:FOO) where the user's package is


More likely the extension symbols would be moved to one or more

extensions packages, e.g. ACME-COMMON-LISP, so user packages in which

the extensions were desired could simply :USE the extensions package(s).

Implementations might want to use this way of conforming with this

proposal in order to minimize cost to users.

In many cases where an extension symbol FOO is used by explicit package

prefix, such as LISP:FOO, it should be easy to search for `LISP:FOO' or

even `LISP:' to find the cases.

Cost of Non-Adoption:

The potential for the LISP package to be adulterated and for supposedly

portable programs to have difficulty getting a foothold in some

implementations will be `noticeably non-zero'.


Portability of some programs will be enhanced.


This change probably supports the naive expectation of most programmers

writing portable code.


This proposal basically affects what implementors are allowed to do;

it says that portable programs can rely on a standard initial package

structure with the same symbols in it. A separate proposal,

LISP-SYMBOL-REDEFINITION, discusses the restrictions on portable

programs as far as redefining LISP symbols.

Whether the USER package may contain symbols other than those

specified in the standard was controversial. The smart programmer

of portable code will never rely on the contents of the

USER package. However, if someone wants a completely empty

package that uses only Lisp, it's easy and portable to create one.

While it would improve portability slightly to disallow additional internal

symbols in the LISP package (since it affects what DO-SYMBOLS will do)

explicitly prohibiting a common practice didn't seem like the best way

to discourage a possibly troublesome implementation technique.

Implementors should be especially careful about accidentally

exporting unwanted additional definitions for symbols,e.g., a variable

definition for EVALHOOK which might show through because of

an unintended name collision.

It is likely that the recently included portions of the standard (CLOS and

the signal mechanism) will reside in their own packages. These externally

defined packages should have the same constraints as outlined for

the LISP package here.

There has been a suggestion that vendor-specific extensions should

be placed in a package named like ACME-COMMON-LISP for the "Acme"


A registry of packages (as well as features, modules and other global

names) would be useful, although probably not a part of the language

standard, per se.

Barrett and Pitman support superseding version 7 with version 8.


Additional comments on the write-up:

"This is clearly correct." --Moon (9 Jan 90)

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