3.3.3 – Assignment Lua allows multiple assignments. Therefore, the syntax for assignment defines a list of variables on the left side and a list of expressions on the right side. The elements in both lists are separated by commas: stat ::= varlist ‘=’ explist varlist ::= var {‘,’ var} explist ::= exp {‘,’ exp} Expressions are discussed in §3.4. Before the assignment, the list of values is adjusted to the length of the list of variables. If there are more values than needed, the excess valu

3.4.2 – Bitwise Operators Lua supports the following bitwise operators: &: bitwise AND |: bitwise OR ~: bitwise exclusive OR >>: right shift <<: left shift ~: unary bitwise NOT All bitwise operations convert its operands to integers (see §3.4.3), operate on all bits of those integers, and result in an integer. Both right and left shifts fill the vacant bits with zeros. Negative displacements shift to the other direction; displacements with absolute values equal to o

3.3.1 – Blocks A block is a list of statements, which are executed sequentially: block ::= {stat} Lua has empty statements that allow you to separate statements with semicolons, start a block with a semicolon or write two semicolons in sequence: stat ::= ‘;’ Function calls and assignments can start with an open parenthesis. This possibility leads to an ambiguity in Lua's grammar. Consider the following fragment: a = b + c (print or io.write)('done') The grammar could see it in two ways:

3.3.2 – Chunks The unit of compilation of Lua is called a chunk. Syntactically, a chunk is simply a block: chunk ::= block Lua handles a chunk as the body of an anonymous function with a variable number of arguments (see §3.4.11). As such, chunks can define local variables, receive arguments, and return values. Moreover, such anonymous function is compiled as in the scope of an external local variable called _ENV (see §2.2). The resulting function always has _ENV as its only upvalue, even if

3.4.3 – Coercions and Conversions Lua provides some automatic conversions between some types and representations at run time. Bitwise operators always convert float operands to integers. Exponentiation and float division always convert integer operands to floats. All other arithmetic operations applied to mixed numbers (integers and floats) convert the integer operand to a float; this is called the usual rule. The C API also converts both integers to floats and floats to integers, as needed. M

collectgarbage ([opt [, arg]]) This function is a generic interface to the garbage collector. It performs different functions according to its first argument, opt: "collect": performs a full garbage-collection cycle. This is the default option. "stop": stops automatic execution of the garbage collector. The collector will run only when explicitly invoked, until a call to restart it. "restart": restarts automatic execution of the garbage collector. "count": returns the total memory

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).

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,

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

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.