Ubuntu Manpage: tm - Facilities for locating and loading of Tcl Modules

Provided by: tcl9.0-doc_9.0.1+dfsg-1_all

NAME

       tm - Facilities for locating and loading of Tcl Modules

SYNOPSIS

       ::tcl::tm::path add ?path...?
       ::tcl::tm::path remove ?path...?
       ::tcl::tm::path list
       ::tcl::tm::roots paths
________________________________________________________________________________________________________________

DESCRIPTION

This document describes the facilities for locating and loading Tcl Modules (see MODULE DEFINITION for
the definition of a Tcl Module). The following commands are supported:

::tcl::tm::path add ?path...?
The paths are added at the head to the list of module paths, in order of appearance. This means
that the last argument ends up as the new head of the list.

The command enforces the restriction that no path may be an ancestor directory of any other path
on the list. If any of the new paths violates this restriction an error will be raised, before any
of the paths have been added. In other words, if only one path argument violates the restriction
then none will be added.

If a path is already present as is, no error will be raised and no action will be taken.

Paths are searched later in the order of their appearance in the list. As they are added to the
front of the list they are searched in reverse order of addition. In other words, the paths added
last are looked at first.

::tcl::tm::path remove ?path...?
Removes the paths from the list of module paths. The command silently ignores all paths which are
not on the list.

::tcl::tm::path list
Returns a list containing all registered module paths, in the order that they are searched for
modules.

::tcl::tm::roots paths
Similar to path add, and layered on top of it. This command takes a single argument containing a
list of paths, extends each with “tclX/site-tcl”, and “tclX/X.y”, for major version X of the Tcl
interpreter and minor version y less than or equal to the minor version of the interpreter, and
adds the resulting set of paths to the list of paths to search.

This command is used internally by the system to set up the system-specific default paths.

The command has been exposed to allow a build system to define additional root paths beyond those
described by this document.

MODULE DEFINITION

       A  Tcl  Module  is a Tcl Package contained in a single file, and no other files required by it. This file
       has to be sourceable. In other words, a Tcl Module is always imported via:

              source module_file

       The load command is not directly used. This restriction is not an actual limitation, as some may believe.
       Ever since 8.4 the Tcl source command reads only until the first ^Z character. This allows us to  combine
       an arbitrary Tcl script with arbitrary binary data into one file, where the script processes the attached
       data in any it chooses to fully import and activate the package.

       The name of a module file has to match the regular expression:

              ([_[:alpha:]][:_[:alnum:]]*)-([[:digit:]].*)\.tm

       The  first  capturing  parentheses  provides  the  name of the package, the second clause its version. In
       addition to matching the pattern, the extracted version number must not raise an error when used  in  the
       command:

              package vcompare $version 0

FINDING MODULES

       The directory tree for storing Tcl modules is separate from other parts of the filesystem and independent
       of auto_path.

       Tcl Modules are searched for in all directories listed in the result of the command ::tcl::tm::path list.
       This  is  called  the  Module  path.  Neither  the auto_path nor the tcl_pkgPath variables are used.  All
       directories on the module path have to obey one restriction:

              For any two directories, neither is an ancestor directory of the other.

       This is required to avoid ambiguities in package naming. If for example the two  directories  “foo/”  and
       “foo/cool”  were on the path a package named cool::ice could be found via the names cool::ice or ice, the
       latter potentially obscuring a package named ice, unqualified.

       Before the search is started, the name of the requested package is translated into a partial path,  using
       the following algorithm:

              All  occurrences  of  “::” in the package name are replaced by the appropriate directory separator
              character for the platform we are on. On Unix, for example, this is “/”.

       Example:

              The requested package is encoding::base64. The generated partial path is “encoding/base64”.

       After this translation the package is looked for in all module paths, by combining them one-by-one, first
       to last with the partial path to form a complete search pattern. Note that the search  algorithm  rejects
       all  files  where  the  filename  does  not  match  the  regular  expression  given in the section MODULE
       DEFINITION. For the remaining files provide scripts are generated  and  added  to  the  package  ifneeded
       database.

       The  algorithm falls back to the previous unknown handler when none of the found module files satisfy the
       request. If the request was satisfied the fall-back is ignored.

       Note that packages in module form have no control over the index and provide  scripts  entered  into  the
       package database for them.  For a module file MF the index script is always:

              package ifneeded PNAME PVERSION [list source MF]

       and the provide script embedded in the above is:

              source MF

       Both  package name PNAME and package version PVERSION are extracted from the filename MF according to the
       definition below:

              MF = /module_path/PNAME′-PVERSION.tm

       Where PNAME′ is the partial path of the module as defined in section FINDING MODULES, and translated into
       PNAME by changing all directory separators to “::”, and module_path is the path (from the list  of  paths
       to search) that we found the module file under.

       Note  also  that we are here creating a connection between package names and paths. Tcl is case-sensitive
       when it comes to comparing package names, but there are filesystems which are  not,  like  NTFS.  Luckily
       these filesystems do store the case of the name, despite not using the information when comparing.

       Given  the above we allow the names for packages in Tcl modules to have mixed-case, but also require that
       there are no collisions when comparing names in a case-insensitive manner. In other words, if  a  package
       Foo is deployed in the form of a Tcl Module, packages like foo, fOo, etc. are not allowed anymore.

DEFAULT PATHS

The default list of paths on the module path is computed by a tclsh as follows, where X is the major
version of the Tcl interpreter and y is less than or equal to the minor version of the Tcl interpreter.

All the default paths are added to the module path, even those paths which do not exist. Non-existent
paths are filtered out during actual searches. This enables a user to create one of the paths searched
when needed and all running applications will automatically pick up any modules placed in them.

The paths are added in the order as they are listed below, and for lists of paths defined by an
environment variable in the order they are found in the variable.

SYSTEM SPECIFIC PATHS
file normalize [info library]/../tclX/X.y
In other words, the interpreter will look into a directory specified by its major version and
whose minor versions are less than or equal to the minor version of the interpreter.

For example for Tcl 8.4 the paths searched are:

[info library]/../tcl8/8.4
[info library]/../tcl8/8.3
[info library]/../tcl8/8.2
[info library]/../tcl8/8.1
[info library]/../tcl8/8.0

This definition assumes that a package defined for Tcl X.y can also be used by all interpreters
which have the same major number X and a minor number greater than y.

file normalize EXEC/tclX/X.y
Where EXEC is file normalize [info nameofexecutable]/../lib or file normalize [::tcl::pkgconfig
get libdir,runtime]

This sets of paths is handled equivalently to the set coming before, except that it is anchored in
EXEC_PREFIX. For a build with PREFIX = EXEC_PREFIX the two sets are identical.

SITE SPECIFIC PATHS
file normalize [info library]/../tclX/site-tcl
Note that this is always a single entry because X is always a specific value (the current major
version of Tcl).

USER SPECIFIC PATHS
$::env(TCLX_y_TM_PATH)
A list of paths, separated by either : (Unix) or ; (Windows). This is user and site specific as
this environment variable can be set not only by the user's profile, but by system configuration
scripts as well.

$::env(TCLX.y_TM_PATH)
Same meaning and content as the previous variable. However the use of dot '.' to separate major
and minor version number makes this name less to non-portable and its use is discouraged. Support
of this variable has been kept only for backward compatibility with the original specification,
i.e. TIP 189.

These paths are seen and therefore shared by all Tcl shells in the $::env(PATH) of the user.

Note that X and y follow the general rules set out above. In other words, Tcl 9.1, for example, will look
at these 4 environment variables:

$::env(TCL9.1_TM_PATH) $::env(TCL9_1_TM_PATH)
$::env(TCL9.0_TM_PATH) $::env(TCL9_0_TM_PATH)

Paths initialized from the environment variables undergo tilde substitution (see filename). Any path
whose tilde substitution fails because the user is unknown will be omitted from search paths.

KEYWORDS

       modules, package

Tcl                                                    8.5                                              tm(3tcl)