TIP 631: ledit - a generalized insert/delete command for list variables

Bounty program for improvements to Tcl and certain Tcl packages.
Author:		Ashok P. Nadkarni <[email protected]>
State:		Final
Type:		Project
Vote:		Done
Created:	6-Aug-2022
Tcl-Version:	8.7
Tcl-Branch:	tip-631
Keywords:	list
Vote-Summary:	Accepted 6/0/0
Votes-For:	BG, KW, KK, MC, SL, FV
Votes-Against:	none
Votes-Present:	none


Add a command to efficiently delete and insert multiple elements in list values stored in variables.


Tcl provides commands lappend, lpop and lset to efficiently operate on unshared list values stored in variables. The efficiency of these commands is a result of its operating on variables containing unshared values which can then be modified in place, generally without needing reallocation or copying as extra trailing free space is present in the list internal representation.

There is however no equivalent for the lreplace command which operates on list values and subsumes several different insert/delete/replace functions. The TIP 625 implementation also allows for leading free space and subranges in the internal representation. This opens the door for more efficient operation in several situations and hence the motivation for this TIP.


The ledit command has the following syntax:

ledit listVar first last ?element element ...?

The command fetches the list value in variable listVar and replaces the elements in the range given by indices first to last (inclusive) with the element arguments. The resulting value is then stored back in the listVar variable. The indices follow the standard Tcl index format supporting simple index arithmetic and indices relative to the end using the end keyword.

Some special cases are:


The command subsumes "lprepend" (lappend analogue for front insertions) or "linject" (linsert analogue for variables) though they would be a little more intuitive to use.

Name conflicts

As a data point, this name is not found in the entire magicsplat distribution with source for over a hundred packages and extensions.

Concerns were voiced on the chat that ledit is easily confused with subst. The name lupdate was suggested though one might argue that can be confused with update.

The author has no particular objection to choosing a different name.


This document has been placed in the public domain.