TIP:            251
Title:          Enhance the 'list' Command
Version:        $Revision: 1.14 $
Author:         Brian Schmidt <contact@schmidtsrus.net>
Author:         Sérgio Loureiro <srgloureiro@gmail.com>
State:          Rejected
Type:           Project
Vote:           Done
Created:        28-Jun-2005
Post-History:   
Tcl-Version:    8.6

~ Abstract

This TIP proposes enhancing the existing '''list''' command to serve as a
top-level command ensemble for all the related list commands that have
proliferated over time, as well as making it easier to add future new
list-based commands.

~Rationale

There are numerous top-level commands for lists already. This command would
centralize them, making it easier for new developers of Tcl scripts to learn
all the related list commands, to simplify and reduce the number of top-level
commands to learn, etc. The enhanced '''list''' would be consistent with the
new top-level commands '''chan''' [208] and '''dict''' [111], as well as the
existing '''string''' and '''file''' commands.

~Specification

A new command '''list''' will be added with the following syntax:

 list append:     equivalent to '''lappend'''

 list create:     equivalent to '''list'''

 list index:      equivalent to '''lindex'''

 list insert:     equivalent to '''linsert'''

 list join:       equivalent to '''join'''

 list length:     equivalent to '''llength'''

 list range:      equivalent to '''lrange'''

 list repeat:     equivalent to '''lrepeat''' (see [136])

 list replace:    equivalent to '''lreplace'''

 list search:     equivalent to '''lsearch'''

 list set:        equivalent to '''lset'''

 list sort:       equivalent to '''lsort'''

Each represents the existing command that is commented. The arguments to each
would remain what the current command takes.

Note that '''split''' is not included as it operates on a string and returns a
list, and '''concat''' is not included because it can operate on both normal
strings and lists.

The old commands could then potentially be deprecated:

 * '''join'''

 * '''lappend'''

 * '''lindex'''

 * '''linsert'''

 * '''llength'''

 * '''lrange'''

 * '''lrepeat'''

 * '''lreplace'''

 * '''lsearch'''

 * '''lset'''

 * '''lsort'''

~Incompatabilities

Incompatability with the existing list command could potentially be solved by
allowing the list command ''without'' one of the defined options to be
shorthand for the new '''list create''' command option. If the first argument
to the new list command is not one of the new known options then '''list
create''' is assumed by default.

For example,

|list {my list}

would be equivalent to:

|list set {my list} {}

It appears the only existing scripts that would break would be those that
actually utilize the '''list''' command, has at least 2 arguments, and have as
their first argument one of the new list command's ensemble options. This
would likely result in a small minority of scripts being impacted. Only Tcl
code with lists defined ''exactly'' as follows would break:

|list append ?arg...
|list create ?arg...
|list index ?arg...
|list insert ?arg...
|list join ?arg... 
|list length ?arg...
|list range ?arg...
|list repeat ?arg...
|list replace ?arg...
|list search ?arg...
|list set ?arg...
|list sort ?arg...

~Copyright

This document has been placed in the public domain.