Loops

Loops repeat a block of code so you do not have to write it several times.

Numeric for loop

Use a numeric for loop when you know the range:

for i = 1, 3 do
    lh.drawln(i)
end

This draws 1, 2, and 3 on separate lines. The limit is included if the counter reaches it.

The optional third number is the step. It defaults to 1. A negative step counts down:

for i = 5, 1, -2 do
    lh.drawln(i) -- Output: 5, then 3, then 1
end

Use a nonzero step. The start, limit, and step are evaluated once before the loop begins. The counter is local to the loop; do not change it inside the body.

while loop

while checks its condition before each repetition. It may never run:

local i = 1

while i <= 3 do
    lh.drawln(i)
    i = i + 1
end

This produces the same output as the first for example.

repeat .. until loop

repeat checks its condition after running the body. It always runs at least once, and stops when the condition becomes truthy:

local i = 1

repeat
    lh.drawln(i)
    i = i + 1
until i > 3

There is no end after until.

Caution

Make sure your loop can finish. Forgetting i = i + 1 in the while example would make it repeat forever. Do not use a loop to wait for the next game tick; use a callback instead.

Looping through tables

A table can hold a list or named values. Generic for loops let you visit its entries.

Use ipairs() for a list, starting at index 1:

local labels = { "FPS", "Position", "Biome" }

for index, label in ipairs(labels) do
    lh.drawln(index .. ": " .. label)
end

This draws 1: FPS, 2: Position, and 3: Biome in order. ipairs() stops at the first missing (nil) entry.

Use pairs() for all keys and values, including named keys:

local settings = { scale = 2, visible = true }

for key, value in pairs(settings) do
    lh.drawln(key .. ": " .. tostring(value))
end

pairs() does not guarantee an order. Use a list and ipairs() when display order matters.

Stopping early

break exits the innermost loop:

for i = 1, 10 do
    if i > 3 then
        break
    end
    lh.drawln(i) -- Only draws 1, 2, and 3.
end

Lua 5.2 has no continue keyword. Put the code you want to run inside an if instead:

for i = 1, 4 do
    if i ~= 2 then
        lh.drawln(i) -- Skips 2.
    end
end