dpans/concept-logical-pathnames.tex

% -*- Mode: TeX -*-

\beginSubsection{Syntax of Logical Pathname Namestrings}
\DefineSection{LogPathNamestrings}

\issue{PATHNAME-LOGICAL:ADD}
The syntax of a \term{logical pathname} \term{namestring} is as follows.
%Added for clarity. -kmp 26-Jun-93
(Note that unlike many notational descriptions in this document,
 this is a syntactic description of character sequences,
 not a structural description of \term{objects}.)

\auxbnf{logical-pathname}%
{\brac{\down{host} \param{host-marker}} \CR
 \brac{\down{\param{relative-directory-marker}}}
 \star{\curly{\down{directory} \param{directory-marker}}} \CR
 \brac{\down{name}} 
 \brac{\param{type-marker} \down{type} 
 \brac{\param{version-marker} \down{version}}}}

\auxbnf{host}{\down{word}}
\auxbnf{directory}{\down{word} | \down{wildcard-word} | \down{wild-inferiors-word}}
\auxbnf{name}{\down{word} | \down{wildcard-word}}
\auxbnf{type}{\down{word} | \down{wildcard-word}}
\auxbnf{version}{\down{pos-int} | \param{newest-word} | \param{wildcard-version}}

\param{host-marker}---a \term{colon}.

\param{relative-directory-marker}---a \term{semicolon}.

\param{directory-marker}---a \term{semicolon}.

\param{type-marker}---a \term{dot}.

\param{version-marker}---a \term{dot}.

\param{wild-inferiors-word}---The two character sequence ``\f{**}'' (two \term{asterisks}).

\param{newest-word}---The six character sequence ``\f{newest}'' 
		   or the six character sequence ``\f{NEWEST}''.

\param{wildcard-version}---an \term{asterisk}.

\param{wildcard-word}---one or more \term{asterisks}, uppercase letters,
   digits, and hyphens, including at least one \term{asterisk}, 
   with no two \term{asterisks} adjacent.

\param{word}---one or more uppercase letters, digits, and hyphens.

\param{pos-int}---a positive \term{integer}.

\beginsubsubsection{Additional Information about Parsing Logical Pathname Namestrings}

\beginsubsubsubsection{The Host part of a Logical Pathname Namestring}

The \param{host} must have been defined as a \term{logical pathname} host;
this can be done by using \macref{setf} of \funref{logical-pathname-translations}.

The \term{logical pathname} host name \f{"SYS"} is reserved for the implementation.
The existence and meaning of \f{SYS:} \term{logical pathnames} 
is \term{implementation-defined}.
 
\endsubsubsubsection%{The Host part of a Logical Pathname Namestring}

\beginsubsubsubsection{The Device part of a Logical Pathname Namestring}
 
There is no syntax for a \term{logical pathname} device since
the device component of a \term{logical pathname} is always \kwd{unspecific};
\seesection\LogicalPathCompUnspecific.

\endsubsubsubsection%{The Device part of a Logical Pathname Namestring}

\beginsubsubsubsection{The Directory part of a Logical Pathname Namestring}

If a \param{relative-directory-marker} precedes the \param{directories},
the directory component parsed is as \term{relative};
otherwise, the directory component is parsed as \term{absolute}.

If a \param{wild-inferiors-marker} is specified,
it parses into \kwd{wild-inferiors}.
 
\endsubsubsubsection%{The Directory part of a Logical Pathname Namestring}

\beginsubsubsubsection{The Type part of a Logical Pathname Namestring}

The \param{type} of a \term{logical pathname} for a \term{source file}
is \f{"LISP"}.   This should be translated into whatever type is 
appropriate in a physical pathname.
 
\endsubsubsubsection%{The Type part of a Logical Pathname Namestring}

\beginsubsubsubsection{The Version part of a Logical Pathname Namestring}

Some \term{file systems} do not have \param{versions}. 
\term{Logical pathname} translation to such a \term{file system}
ignores the \param{version}.
This implies that a program cannot rely on being able to store
more than one version of a file named by a \term{logical pathname}.

If a \param{wildcard-version} is specified,
it parses into \kwd{wild}.

\endsubsubsubsection%{The Version part of a Logical Pathname Namestring}

\beginsubsubsubsection{Wildcard Words in a Logical Pathname Namestring}

Each \term{asterisk} in a \param{wildcard-word} matches a sequence of 
zero or more characters.  The \param{wildcard-word} ``\f{*}'' 
parses into \kwd{wild}; other \term{wildcard-words} parse into \term{strings}.
 
\endsubsubsubsection%{Wildcard Words in a Logical Pathname Namestring}

\beginsubsubsubsection{Lowercase Letters in a Logical Pathname Namestring}

When parsing \param{words} and \param{wildcard-words},
lowercase letters are translated to uppercase.

\endsubsubsubsection%{Lowercase Letters in a Logical Pathname Namestring}

\beginsubsubsubsection{Other Syntax in a Logical Pathname Namestring}

The consequences of using characters other than those specified here
in a \term{logical pathname} \term{namestring} are unspecified.

%% !!! What does this mean??  This section is supposed to be about syntax, 
%%     not component values.  Sigh.  -kmp 26-Jun-93
The consequences of using any value not specified here as a 
\term{logical pathname} component are unspecified.

\endsubsubsubsection%{Other Syntax in a Logical Pathname Namestring}

%This wasn't a valid reference.
%See ``Input/Output'' for parsing and file manipulation details.
\endissue{PATHNAME-LOGICAL:ADD}

\endsubsubsection%{Additional Information about Parsing Logical Pathname Namestrings}

\endSubsection%{Syntax of Logical Pathname Namestrings}

\beginSubsection{Logical Pathname Components}

\beginsubsubsection{Unspecific Components of a Logical Pathname}
\DefineSection{LogicalPathCompUnspecific}

The device component of a \term{logical pathname} is always \kwd{unspecific};
no other component of a \term {logical pathname} can be \kwd{unspecific}.  

\endsubsubsection%{Unspecific Components of a Logical Pathname}

\beginsubsubsection{Null Strings as Components of a Logical Pathname}

The null string, \f{""}, is not a valid value for any component of a \term{logical pathname}.
%% I removed the following because:
%%   - it's redundant with the syntax info above
%%   - I doubt it's really the reason
%%   - it's not sufficient to cause this: e.g., you might assume that
%%       (probe-file "X:FOO;*.LISP") could return a logical pathname containing
%%     a null string name even though you didn't type it in, since * is not a zero-char
%%     string but only matches one.  The resulting logical pathname might have no 
%%     printed representation.  But the previous sentence makes a stronger claim:  it
%%     says that there is no such file, whether printable or not.  So the following
%%     cannot be the reason.
%%  -kmp 26-Jun-93
%
% since it is neither a \param{word} nor a \param{wildcard-word}.

\endsubsubsection%{Null Strings as Components of a Logical Pathname}

\endSubsection%{Logical Pathname Components}