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 vale is included, it's sign should agree with the direction of the sequence (descending → negative and ascending → positive), otherwise an empty list is returned. For example:
% lseq 1 to 5 ;# increasing → 1 2 3 4 5 % lseq 5 to 1 ;# decreasing → 5 4 3 2 1 % lseq 6 to 1 by 2 ;# decreasing, step wrong sign, empty list % lseq 1 to 5 by 0 ;# all step sizes of 0 produce an empty list
The numeric arguments, start, end, step, and count, may also be a valid expression. The expression will be evaluated and the numeric result will be used. An expression that does not evaluate to a number will produce an invalid argument error.
Start defines the initial value and end defines the limit, not necessarily the last value. lseq produces a list with count elements, and if count is not supplied, it is computed as:
count = int( (end - start + step) / step )
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
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