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lset(n)                      Tcl Built-In Commands                     lset(n)




NAME

       lset - Change an element in a list


SYNOPSIS

       lset varName ?index ...? newValue


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 the number of elements in $var-
       Name, 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 string index, 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 previ-
       ous  indexing  operation, allowing the script to alter elements in sub-
       lists (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.


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), string(n)


KEYWORDS

       element, index, list, replace, set



Tcl                                   8.4                              lset(n)

tcl 8.6.0 - Generated Thu Jan 10 14:31:15 CST 2013
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