lseq(n)

📦
version 9.0.3 · 2 versions
, in alpine 3.23, alpine 3.24, fedora 43, fedora 44, nixos 26.05

🎀 lseq(n) — bestie, let's build a whole numeric sequence 🎀

ok so this is the manual page for lseq, a Tcl Built-In Command, and honestly? it's giving "make me a list of numbers real quick" and I am obsessed. no cap, it does exactly what it says on the tin and the tin is cute.

✨ 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?

like… look at those forms. three whole moods. pick ur fighter 💅

💖 DESCRIPTION 💖

The lseq command creates a sequence of numeric values — and those values can be either wide integers or doubles — using the parameters you hand it: start, end, and step. The operation argument .. or to is what defines the range. The count option is used to define a count of the number of elements in the list. And there's a short form too: if you just give it a single count value, it'll create a range from 0 to count-1. iconic behavior honestly ✨

lseq can produce both increasing and decreasing sequences, bestie. 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. But if a step value is included, its sign should agree with the direction of the sequence (descending → negative, ascending → positive), otherwise an empty list is returned. like, nothing. ghosted. 💀 for example:

              % lseq 1 to 5    ;# increasing
              → 1 2 3 4 5

              % lseq 5 to 1    ;# decreasing
              → 5 4 3 2 1

              % lseq 0 0.5 by 0.1  ;# doubles
              → 0.0 0.1 0.2 0.3 0.4 0.5

              % 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. But heads up: an expression that does not evaluate to a number will produce an invalid argument error. so keep it numeric, babe 🙈

Start defines the initial value, and end defines the limit — not necessarily the last value, ok? important distinction, don't come for me. lseq produces a list with count elements, and if count is not supplied, it is computed as:

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

math girlies rise 🧮💜

🌈 EXAMPLES 🌈

ok this is the fun part. watch:

              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

the range check one? main character energy. and that last one literally squares everything, ate and left no crumbs 🔥

👑 SEE ALSO 👑

run don't walk to these besties:

💅 KEYWORDS 💅

element, index, list — the holy trinity fr fr 🌸

ok that's the whole page, no skips, no cap. go make some sequences, bestie 💖

and that's a wrap!! this was the lseq(n) page from Tcl 9.0 🫶 mwah, tysm for reading, go forth and sequence responsibly ✨👑

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