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Status: passed, as amended here, Jun 89 X3J13


References: Pathnames (pp410-413),







Related-issues: PATHNAME-WILD

Category: CHANGE

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

22-Mar-89, Version 2 by Moon, update and rewrite

9-May-89, Version 3 by Moon, remove alternate proposals

9-May-89, Version 4 by Moon, respond to discussion with KMP

17-Jun-89, Version 5 by Moon, fix typo, make minor improvements

to the presentation.

1-Jul-89, Version 6 by Masinter, as per Jun89X3J13 amendments

Problem Description:

Issues of alphabetic case in pathnames are a major source of problems.

In some file systems, the customary case is lowercase, in some uppercase,

in some mixed. In some file systems, case matters, in others it does


There are two kinds of pathname case portability problems: moving

programs from one Common Lisp to another, and moving pathname component

values from one file system to another. To solve the first problem, all

Common Lisp implementations that support a particular file system must

use compatible representations for pathname component values. To solve

the second problem, there must be a common representation for the least

common denominator pathname component values that exist on all

interesting file systems.

This desire for a common representation directly conflicts with the

desire among programmers who only use one file system to work with the

local conventions and not think about issues of porting to other file

systems. The common representation cannot be the same as every local

convention, since they vary.

In the current anarchy of pathname component case conventions:


will produce foo.lisp in some Unix Common Lisp implementations

and will produce FOO.LISP in other Unix Common Lisp implementations.


will produce FOO.LISP in some Tops-20 Common Lisp implementations

and will produce "^Vf^Vo^Vo.^Vl^Vi^Vs^Vp"in other Tops-20 Common

Lisp implementations.

Problems like this make it difficult to use MAKE-PATHNAME for much of

anything without corrective (non-portable) code.

Other problems occur in merging because doing



should probably return "MY-TOPS-20:FOO.LISP" but in fact might return

"MY-TOPS-20:FOO.^Vl^Vi^Vs^Vp" in some implementations.

Problems like this make it difficult to use any merging primitives for

much of anything without corrective (non-portable) code.


Add a keyword argument :CASE to MAKE-PATHNAME, PATHNAME-HOST,


The possible values for the argument are :COMMON and :LOCAL.

:LOCAL means strings input to MAKE-PATHNAME or output by PATHNAME-xxx

follow the local file system's conventions for alphabetic case.

Strings given to MAKE-PATHNAME will be used exactly as written if

the file system supports both cases. If the file system only

supports one case, the strings will be translated to that case.

:COMMON means strings input to MAKE-PATHNAME or output by PATHNAME-xxx

follow this common convention:

- all uppercase means to use a file system's customary case.

- all lowercase means to use the opposite of the customary case.

- mixed case represents itself.

The second and third bullets exist so that translation from local to

common and back to local is information-preserving.

The default is :LOCAL.

Namestrings always use local file system case conventions.


input pathnames into customary case in the output pathname.

Implications of the proposal:

Unix is case-sensitive and prefers lowercase, so it translates between

common and local by inverting the case of non-mixed-case strings.

Tops-20 is case-sensitive and prefers uppercase, so it uses identical

representations for common and local.

VAX/VMS is upper-case-only (that is, the file system translates all file

name arguments to upper case), so it translates common to local by

upcasing, and translates local to common with no change.

Macintosh is case-insensitive and prefers lowercase, so it translates

between common and local by inverting the case of non-mixed-case strings,

and ignores case in EQUAL of two pathnames.

Test Case/Examples:






:CASE :LOCAL) => "foo"






:CASE :LOCAL) => "TeX"




This does not solve the whole pathname problem, but it does improve

the situation for a clearly defined set of very common problems.

Together with the other pathname proposals, the behavior of pathnames

should be sufficiently consistent across Common Lisp implementations

and across file systems to allow portability of pathname-manipulating


The current situation where different implementations talk about

the *same* file system in different ways will be corrected by this

and some of the other pathname proposals.

Upper case is chosen as the common case for no better reason than

consistency with Lisp symbols.

The :CASE keyword argument provides access to both common and local

conventions without introducing any new functions. The default

convention is the common one, assuming that most programs are fully

portable and therefore :COMMON will be more frequently used.

Current Practice:

There are no known implementations of exactly what is proposed.

Symbolics Genera uses common case normally, and provides a way to

access the local case (called "raw") that in practice is rarely used.

Symbolics Genera's own file system is case-insensitive and uses lower

case as the customary case, but transparent network access is available

to file systems using all known case conventions.

Several Common Lisp implementations behave as if :CASE :LOCAL was

specified (but accept no :CASE argument).

Cost to Implementors:

The :CASE feature is easily added, but some implementations may have

to change the default behavior when :CASE is not specified. No

implementation need change its internal representation, nor the way

pathnames print, just the interface functions listed above.

Cost to Users:

Technically, this change is upward compatible.

In fact, since the existing CLtL spec is so poor, nearly everyone relies

heavily on implementation-specific behavior since there is little other

choice. As such, any change is almost certain to break lots of programs,

in usually superficial but nevertheless important ways. However, if we

really make the pathname facility more portable, the user community may

be willing to bear the consequences of these changes.

Cost of Non-Adoption:

We would be contributing to the perpetuation of the existing fiasco of a

pathname system.

Performance Impact:



One step closer to a usable pathname system.


Anything that simplifies the user model of pathnames is an improvement.


Some people would rather use lowercase as the common case. The

decision is essentially arbitrary. Everywhere else in Common Lisp

where case matters, uppercase was chosen.

It has been proposed that the Common Lisp specification should include

specifications of the exact behavior of pathnames for several popular

operating systems, so that multiple implementations for those

operating systems would be compatible with each other. This proposal

does that for alphabetic case.

Some people want the default for :CASE to be :LOCAL instead of :COMMON.

See Rationale.

There should probably be a remark somewhere that says that portable

programs shouldn't expect to be able to create and/or access distinct

files whose pathname components differ only in case.

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