Lua

Lua (Portuguese for “moon”) was created in 1993 at the Pontifical Catholic University of Rio de Janeiro by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, and Waldemar Celes. It was built to be embedded in larger programs, and it’s small and fast enough that it now runs inside game engines, Roblox, the Neovim editor, and network tools.

Lua has one data structure, the table. The same table type serves as an array, a dictionary, a record, and an object, depending on which keys you use. Arrays are tables whose keys are 1, 2, 3, and so on, and #t gives their length. The standard library is small: string patterns, table.sort, math, and file input and output. There’s no split, no round, and no CSV reader, and modules from LuaRocks, Lua’s package manager, aren’t installed here.

Quirks

• Indexes start at 1. With a = {10, 20, 30}, a[1] is 10 and a[0] is nil, not an error.
• 0 and the empty string are true. Only nil and false are false, so 0 and "yes" or "no" gives “yes”.
• / always gives a float, so 10 / 2 is 5.0. // divides and rounds down: 7 // 2 is 3, and -7 // 2 is −4.
• Not equal is ~=, not !=.
• table.sort isn’t stable, so rows with equal keys can come out in any order. Its comparison must be a strict “less than”: sorting with a <= b can stop with “invalid order function for sorting”.
• # is only reliable on an array with no gaps. With h[1], h[2], and h[4] set, #h gave 4, although h[3] is nil.
• Integers wrap around when they overflow: math.maxinteger + 1 is math.mininteger.
• 1 and 1.0 are the same table key, so setting d[1.0] overwrites d[1].

git clone https://github.com/qnixon/dswithx.git
cd dswithx
python3 harness/run_tests.py --language lua