lseq(3tcl)

💖 lseq — bestie, it's the Tcl Built-In Commands page, 3tcl section, and we're building sequences 💖

✨ NAME ✨

lseq — build a numeric sequence and get it back as a list 🎀

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🦋 SYNOPSIS 🦋

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

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🌸 DESCRIPTION 🌸

okay so the lseq command makes a sequence of numeric values — and those values can be wide integers or doubles, your call — using the params start, end, and step. The operation argument .. or to is what defines the range, like it's the little official handshake for "yeah this is a range". The count option is a whole different thing: it defines a count of the number of elements in the list. And there's a short form, where you just hand it a single count value, and boom: a range from 0 to count-1. 🫶

lseq can do both increasing and decreasing sequences, she's versatile like that. When both start and end show up with no step value, then if start <= end, the sequence will be increasing, and if start > end it will be decreasing. But if a step value is included, its sign should agree with the direction of the sequence (descending → negative, ascending → positive), otherwise the list will have a length of 0. like, an empty list, a little nothing-burger. 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, bestie, keep that in mind. 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 )

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💅 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

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👑 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)

the whole list squad fr fr, go read all of them, they're iconic 💜

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⭐ KEYWORDS ⭐

element, index, list

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okay and that's the whole vibe check — this page is straight outta Tcl 9.0, lseq(3tcl), and it literally ate 💅✨ no cap, go build some sequences bestie, you got this 🦋💖🌸🎀