NAME¶

lseq - Build a numeric sequence returned as a list

SYNOPSIS¶

lseq start ?(..|to)? end ??by? step?
lseq start count count ??by? step?
lseq count ?by step?

DESCRIPTION¶

The lseq command creates a sequence of numeric values, which may be either wide integers or doubles, using the given parameters start, end, and step. The operation argument ".." or "to" defines the range. The "count" option is used to define a count of the number of elements in the list. A short form use of the command, with a single count value, will create a range from 0 to count-1.

The lseq command can produce both increasing and decreasing sequences. When both start and end are provided without a step value, then if start <= end, the sequence will be increasing and if start > end it will be decreasing. If a step value is included, it's sign should agree with the direction of the sequence (descending → negative and ascending → positive), otherwise the list will have a length of 0. For example:

# increasing:
% lseq 1 to 5
→ 1 2 3 4 5
# decreasing:
% lseq 5 to 1
→ 5 4 3 2 1
# doubles:
% lseq 0 0.5 by 0.1
→ 0.0 0.1 0.2 0.3 0.4 0.5
# decreasing, step with wrong sign:
% lseq 6 to 1 by 2
→ {}
# step of 0,
% lseq 3 to 9 by 0
→ 3

Start defines the initial value and end defines the limit, not necessarily the last value. lseq produces a list with count elements, always, even if the step value is 0. and if count is not supplied, it is computed as:

count = int( ( (end - start) / step ) + 1 )

EXAMPLES¶

lseq 3
→ 0 1 2
lseq 3 0
→ 3 2 1 0
lseq 10 .. 1 by -2
→ 10 8 6 4 2
set l [lseq 0 -5]
→ 0 -1 -2 -3 -4 -5
lseq 1 count 5 by 0
→ 1 1 1 1 1
foreach i [lseq [llength $l]] {


    puts l($i)=[lindex $l $i]
}
→ l(0)=0
→ l(1)=-1
→ l(2)=-2
→ l(3)=-3
→ l(4)=-4
→ l(5)=-5
foreach i [lseq {[llength $l]-1} 0] {


    puts l($i)=[lindex $l $i]
}
→ l(5)=-5
→ l(4)=-4
→ l(3)=-3
→ l(2)=-2
→ l(1)=-1
→ l(0)=0
set i 17
→ 17
if {$i in [lseq 0 50]} { # equivalent to: (0 <= $i && $i <= 50)


    puts "Ok"
} else {


    puts "outside :("
} → Ok
set sqrs [lmap i [lseq 1 10] { expr {$i*$i} }]
→ 1 4 9 16 25 36 49 64 81 100

SEE ALSO¶

foreach(3tcl), list(3tcl), lappend(3tcl), lassign(3tcl), lindex(3tcl), linsert(3tcl), llength(3tcl), lmap(3tcl), lpop(3tcl), lrange(3tcl), lremove(3tcl), lreplace(3tcl), lreverse(3tcl), lsearch(3tcl), lset(3tcl), lsort(3tcl)

KEYWORDS¶

element, index, list