lset(n)

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NAME

       lset - Change an element in a list

SYNOPSIS

       lset varName ?index...? newValue
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DESCRIPTION

       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 con-
       secutively 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  ele-
       ment  in  it  (0 refers to the first element of the list).  When inter-
       preting the list, lset observes the same rules  concerning  braces  and
       quotes  and  backslashes as the Tcl command interpreter; however, vari-
       able 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 or equal to the number of elements
       in $varName, then an error occurs.

       If index has the value end, it refers to the last element in the  list,
       and end-integer refers to the last element in the list minus the speci-
       fied integer offset.

       If additional index arguments are supplied, then each argument is  used
       in turn to address an element within a sublist designated by the previ-
       ous indexing operation, allowing the script to alter elements  in  sub-
       lists.  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
       strictly  less  than  the  length  of the corresponding list.  In other
       words, the lset command cannot change the size of a list.  If an  index
       is outside the permitted range, an error is reported.

EXAMPLES

       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]]
                => {a b c} {d e f} {g h i}
       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} => j k l
              lset x {} {j k l} => j k l
              lset x 0 j => j {d e f} {g h i}
              lset x 2 j => {a b c} {d e f} j
              lset x end j => {a b c} {d e f} j
              lset x end-1 j => {a b c} j {g h i}
              lset x 2 1 j => {a b c} {d e f} {g j i}
              lset x {2 1} j => {a b c} {d e f} {g j i}
              lset x {2 3} j => list index out of range
       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]]]
               => {{a b} {c d}} {{e f} {g h}}
       The indicated return value also becomes the new value of x.
              lset x 1 1 0 j => {{a b} {c d}} {{e f} {j h}}
              lset x {1 1 0} j => {{a b} {c d}} {{e f} {j h}}

SEE ALSO

       list(n),  lappend(n),  lindex(n),  linsert(n),  llength(n), lsearch(n),
       lsort(n), lrange(n), lreplace(n)

KEYWORDS

       element, index, list, replace, set

Tcl                                   8.4                              lset(n)