Replace elements in a list with new elements 

The documentation for this command can be found at http://www.purl.org/tcl/home/man/tcl8.5/TclCmd/lreplace.htm

 lreplace list first last ?element element ...?  

'''Lreplace''' returns a new list formed by replacing one or more elements of ''list'' with the ''element'' arguments. ''First'' gives the index in ''list'' of the first element to be replaced (0 refers to the first element). If ''first'' is less than zero then it refers to the first element of ''list'';  the element indicated by ''first'' must exist in the list. ''Last'' gives the index in ''list'' of the last element to be replaced. If ''last'' is less than ''first'' then no elements are deleted; the new elements are simply inserted before ''first''. ''First'' or ''last'' may be '''end''' (or any abbreviation of it) to refer to the last element of the list. 

The ''element'' arguments specify zero or more new arguments to be added to the list in place of those that were deleted. Each ''element'' argument will become a separate element of the list. If no ''element'' arguments are specified, then the elements between first and last are simply deleted.  (from: TclHelp)
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Examples:
 % lreplace  {a b c} 0 0 @
 @ b c
 % lreplace  {a b c} 1 1 
 a c
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If the ''last'' argument of lreplace was made optional, one could essentially just alias ldelete to lreplace [CmCc]
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[TFW] Feb 20, 2004 - Inplace replacements

Often time we have a long list we want to replace "in-place", that is without copying the list to a new altered list. Using the [K] combinator it is quite easy. (Note 8.5 is needed for the {expand} syntax)

 proc lipreplace {_list first last args} {
    upvar $_list list
    set list [lreplace [K $list [set list ""]] $first $last {expand}$args]
 }
 > set A [list 1 2 3]
 1 2 3
 > lipreplace A 1 end c d
 1 c d
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''[escargo] 15 Sep 2005'' - Perhaps there is a better place for the following discussion, but this is
where I saw a specific feature mentioned that I want to raise an issue about.

'''List commands bounds checking and associated behavior'''

The description above states (in part):
"If ''first'' is less than zero then it refers to the first element of ''list''."

I see two problems with this:
   * What should the behavior be when indexing outside the bounds of a list?
   * How does this behavior vary from other list operations?

Personally, I see allowing negative indexes (''first'' or ''last'') to be errors, and ones
that are ''silent failures'' at that.  (This is unlike [Icon] where at least some negative indexes have
semantically valid meaning.)  Perhaps list operations that do indexing should have a '''-strict'''
option so that if indexes are outside the proper ranges, errors would be thrown.

On the second issue, [lindex] allows negative indexes (and indexes greater than the length of the list),
but returns no values.  The negative index is not coerced to zero. Thus the same index value (a negative
one) refers to no element with [lindex] but the zeroth element with lreplace.  Perhaps an item for the
[Tcl 9.0 WishList] would be consistent behavior for [list] and [string] indexing semantics.
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See also: [linsert] - [lappend] - [list]
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[Category Command]