lset - Change an element in a list

       The lset command accepts a parameter, varName, which it interprets as the name of a variable containing a
       Tcl  list.   It  also  accepts  zero  or more indices into the list.  The indices may be presented either
       consecutively on the command line, or grouped in a Tcl list and presented as a single argument.  Finally,
       it accepts a new value for an element of varName.

       If no indices are presented, the command takes the form:

              lset varName newValue

       or

              lset varName {} newValue

       In this case, newValue replaces the old value of the variable varName.

       When presented with a single index, the lset command treats the content of the varName variable as a  Tcl
       list.   It  addresses  the  index'th  element  in  it  (0 refers to the first element of the list).  When
       interpreting the list, lset observes the same rules concerning braces and quotes and backslashes  as  the
       Tcl  command  interpreter;  however,  variable  substitution  and command substitution do not occur.  The
       command constructs a new list in which the designated element is replaced with newValue.  This  new  list
       is stored in the variable varName, and is also the return value from the lset command.

       If index is negative or greater than the number of elements in $varName, then an error occurs.

       If index is equal to the number of elements in $varName, then the given element is appended to the list.

       The  interpretation  of  each  simple index value is the same as for the command stringindex, supporting
       simple index arithmetic and indices relative to the end of the list.

       If additional index arguments are supplied, then each argument is used in  turn  to  address  an  element
       within  a sublist designated by the previous indexing operation, allowing the script to alter elements in
       sublists (or append elements to sublists).  The command,

              lset a 1 2 newValue

       or

              lset a {1 2} newValue

       replaces element 2 of sublist 1 with newValue.

       The integer appearing in each index argument must  be  greater  than  or  equal  to  zero.   The  integer
       appearing  in each index argument must be less than or equal to the length of the corresponding list.  In
       other words, the lset command can change the size of a list only by appending an element (setting the one
       after the current end).  If an index is outside the permitted range, an error is reported.

       In each of these examples, the initial value of x is:

              set x [list [list a b c] [list d e f] [list g h i]]
                    →{abc}{def}{ghi}

       The indicated return value also becomes the new value of x (except in the last case, which  is  an  error
       which leaves the value of x unchanged.)

              lset x {j k l}
                    →jkllset x {} {j k l}
                    →jkllset x 0 j
                    →j{def}{ghi}lset x 2 j
                    →{abc}{def}jlset x end j
                    →{abc}{def}jlset x end-1 j
                    →{abc}j{ghi}lset x 2 1 j
                    →{abc}{def}{gji}lset x {2 1} j
                    →{abc}{def}{gji}lset x {2 3} j
                    →{abc}{def}{ghij}lset x {2 4} j
                    →listindexoutofrange

       In the following examples, the initial value of x is:

              set x [list [list [list a b] [list c d]] \
                          [list [list e f] [list g h]]]
                    →{{ab}{cd}}{{ef}{gh}}

       The indicated return value also becomes the new value of x.

              lset x 1 1 0 j
                    →{{ab}{cd}}{{ef}{jh}}lset x {1 1 0} j
                    →{{ab}{cd}}{{ef}{jh}}

       element, index, list, replace, set

Tcl                                                    8.4                                            lset(3tcl)

       lset - Change an element in a list

list(3tcl),   lappend(3tcl),  lassign(3tcl),  ledit(3tcl),  lindex(3tcl),  linsert(3tcl),  llength(3tcl),
       lmap(3tcl),  lpop(3tcl),  lrange(3tcl),  lremove(3tcl),  lrepeat(3tcl),  lreplace(3tcl),  lreverse(3tcl),
       lsearch(3tcl), lseq(3tcl), lsort(3tcl) string(3tcl)

lsetvarName?index...?newValue
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