Command in the [TclX] package.
    :   '''lvarpop''' ''var'' ?''indexExpr''? ?''string''?
The '''lvarpop''' command pops (deletes) the element indexed by the expression ''indexExpr'' from the list contained in the variable ''var''. If ''indexExpr'' is omitted, then 0 is assumed. If ''string'' is specified, then the deleted element is replaced by ''string''. The replaced or deleted element is returned. Thus 
======
  lvarpop argv 0
======
returns the first element of `argv`, setting `argv` to contain the remainder of the string.

If the expression ''indexExpr'' starts with the string "'''end'''", then '''end''' is replaced with the index of the last element in the list. If the expression starts with "'''len'''", then '''len''' is replaced with the length of the list.

See also [lvarpush].

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A quick Tcl-only lvarpop, if you don't want to include all of [Tclx] in your [starpack] or [starkit]:

 proc lvarpop {upVar {index 0}} {
  upvar $upVar list;
  if {![info exists list]} { return "-1" }
  set top [lindex $list $index];
  set list [concat [lrange $list 0 [expr $index - 1]] [lrange $list [expr $index +1] end]]
  return $top;
  }

Sourced from the Wiki somewhere ages ago or perhaps Usenet.

[Lars H]: Simplified implementation, using [lreplace] instead of [lrange]&[concat]:
 proc lvarpop {upVar {index 0}} {
    upvar 1 $upVar list
    if {![info exists list]} { return "-1" }
    set top [lindex $list $index]
    set list [lreplace $list $index $index]
    return $top
 }
Unlike the above, this supports end-relative indices. It will however throw an error if the index is out-of-range.

Neither proc supports general expressions or len-relative indices, as described in the manpage text above. Nor do they support the third argument of [TclX]'s '''lvarpop'''.

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%| [Category Command] | [Category TclX] |%
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