lua

notes on lua

lua

comments

• line: -- a comment
• block: --[[ a comment ]]--

variables

• g = "foo": global variable
• local l = "bar": local (block scoped) variable

builtin, operators

unusual ones

• ^ exponent
• ~=: not
• ..: concat
• print(): print to stdout
• pairs(): iterate over table
• ipairs(): iterate over table, stop at first break

idioms

• a and b or c == a ? b : c
• x = x or v == if not x then x = v end

control flow

do

not really control flow, just a new block

1do
2  -- something
3end

if

1if condition then
2  -- something
3elseif condition then
4  -- something
5else
6  -- something
7end

while, repeat

1-- test before body, repeat until false
2while condition do
3  -- something
4end
5
6-- test after body, repeat until true
7repeat
8  -- something
9until condition

for

1-- numeric, step defaults to 1
2for i = start,finish,step do
3  -- something
4end
5
6-- generic, use with iterators
7for a,b in x do
8  -- something
9end

break

• break: jump out of while,repeat, for

functions

 1-- normal function
 2function function_name (a, b, ...)
 3  -- something
 4  -- access ... with arg[]
 5  return a, b
 6end
 7
 8-- anonymous function, useful in closures
 9function ()
10  return "foo"
11end
12
13-- assign function_name to some_table
14function some_table.function_name ()
15  return "foo"
16end
17
18-- locally scoped function
19local function function_name ()
20  return "foo"
21end

tables

• t = {}: empty table
• t = { "foo"="bar" }: t["foo"] = "bar"
• t = { "foo", "bar" }: t[1] = "foo", t[2] = "bar"

errors

• error("some error"): raise an error
• assert(condition, "some error"): assert, raise an error
• pcall(some_function): catch an error, returns true + values or false + error

special tables

ref lua 5.4 index

• arg: table of args, for scripts, functions with variable args
• _G: table holding globals
• coroutine: coroutine functions, create, yield, resume, ...
• table: table manipulation: insert, remove, sort, concat, ...
• string: string manipulation: len, lower, upper, char, byte, sub, rep, reverse, format, find, gsub, gfind, ...
• io: io functions: lines, read, write, input, output, open, flush, close, stdin, stdout, stderr, ...
  • open: return a file handle with functions: lines, read, write, seek, flush close, ...
• os: date, time, difftime, getenv, execute, exit, ...
• math: ...
• utf8: ...
• debug: ...