debug.debug () Enters an interactive mode with the user, running each string that the user enters. Using simple commands and other debug facilities, the user can inspect global and local variables, change their values, evaluate expressions, and so on. A line containing only the word cont finishes this function, so that the caller continues its execution. Note that commands for debug.debug are not lexically nested within any function and so have no direct access to local variables.

coroutine.yield (···) Suspends the execution of the calling coroutine. Any arguments to yield are passed as extra results to resume.

coroutine.wrap (f) Creates a new coroutine, with body f. f must be a function. Returns a function that resumes the coroutine each time it is called. Any arguments passed to the function behave as the extra arguments to resume. Returns the same values returned by resume, except the first boolean. In case of error, propagates the error.

coroutine.status (co) Returns the status of coroutine co, as a string: "running", if the coroutine is running (that is, it called status); "suspended", if the coroutine is suspended in a call to yield, or if it has not started running yet; "normal" if the coroutine is active but not running (that is, it has resumed another coroutine); and "dead" if the coroutine has finished its body function, or if it has stopped with an error.

coroutine.running () Returns the running coroutine plus a boolean, true when the running coroutine is the main one.

coroutine.resume (co [, val1, ···]) Starts or continues the execution of coroutine co. The first time you resume a coroutine, it starts running its body. The values val1, ... are passed as the arguments to the body function. If the coroutine has yielded, resume restarts it; the values val1, ... are passed as the results from the yield. If the coroutine runs without any errors, resume returns true plus any values passed to yield (when the coroutine yields) or any values returned by the body

coroutine.isyieldable () Returns true when the running coroutine can yield. A running coroutine is yieldable if it is not the main thread and it is not inside a non-yieldable C function.

coroutine.create (f) Creates a new coroutine, with body f. f must be a function. Returns this new coroutine, an object with type "thread".

3.3.4 – Control Structures The control structures if, while, and repeat have the usual meaning and familiar syntax: stat ::= while exp do block end stat ::= repeat block until exp stat ::= if exp then block {elseif exp then block} [else block] end Lua also has a for statement, in two flavors (see §3.3.5). The condition expression of a control structure can return any value. Both false and nil are considered false. All values different from nil and false are considered true (in particular,

3.4.6 – Concatenation The string concatenation operator in Lua is denoted by two dots ('..'). If both operands are strings or numbers, then they are converted to strings according to the rules described in §3.4.3. Otherwise, the __concat metamethod is called (see §2.4).