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







lset - Change an element in a list








lset varName ?index...? newValue










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 or equal to the number
    of elements in $varName, then an error occurs.


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 previous indexing operation, allowing the script to alter elements in
    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 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.








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}}










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












element, index, list, replace, set







  

    8.4
    Tcl