Function Calls

3.4.10 – Function Calls

A function call in Lua has the following syntax:

functioncall ::= prefixexp args

In a function call, first prefixexp and args are evaluated. If the value of prefixexp has type function, then this function is called with the given arguments. Otherwise, the prefixexp "call" metamethod is called, having as first parameter the value of prefixexp, followed by the original call arguments (see §2.4).

The form

functioncall ::= prefixexp ‘:’ Name args

can be used to call "methods". A call v:name(args) is syntactic sugar for v.name(v,args), except that v is evaluated only once.

Arguments have the following syntax:

args ::= ‘(’ [explist] ‘)’
args ::= tableconstructor
args ::= LiteralString

All argument expressions are evaluated before the call. A call of the form f{fields} is syntactic sugar for f({fields}); that is, the argument list is a single new table. A call of the form f'string' (or f"string" or f[[string]]) is syntactic sugar for f('string'); that is, the argument list is a single literal string.

A call of the form return functioncall is called a tail call. Lua implements proper tail calls (or proper tail recursion): in a tail call, the called function reuses the stack entry of the calling function. Therefore, there is no limit on the number of nested tail calls that a program can execute. However, a tail call erases any debug information about the calling function. Note that a tail call only happens with a particular syntax, where the return has one single function call as argument; this syntax makes the calling function return exactly the returns of the called function. So, none of the following examples are tail calls:

return (f(x))        -- results adjusted to 1
return 2 * f(x)
return x, f(x)       -- additional results
f(x); return         -- results discarded
return x or f(x)     -- results adjusted to 1