Quick Lua tutorial

General

• Lua is a dynamically typed language. This means that variables do not have types; only values do. Therefore, there are no type definitions in the language
• All values carry their own type
• Lua is a case-sensitive language

Variables

• Global variables in Lua do not need to be declared.
• Any variable is assumed to be global unless explicitly declared local.
• Local variables may be declared anywhere inside a block: local varname [= initvalue].
• The scope of local variables begins after the declaration and lasts until the end of the block
• The unit of execution of Lua is called a chunk. A chunk is simply a sequence of statements, which are executed sequentially.
• A semicolon can optionally follow each statement.

Identifiers

• They can be any string of letters, digits, and underscores, not beginning with a digit
• As a convention, identifiers starting with underscore followed by uppercase letters (such as _INPUT) are reserved for internal variables
• Reserved words: and, break, do, else, elseif, end, for, function, if, in, local, nil, not, or, repeat, return, then, until, while
• Reserved strings used for operators: ~= <= >= < > == = + - * / ( ) { } [ ] ; , . .. ...

Comments

Start anywhere outside a string with a double hyphen (--) and run until the end of the line

Literal strings

• Delimited by matching single or double quotes, or by matching ... . Literals in this bracketed form may run for several lines, may contain nested ... pairs, and do not interpret escape sequences.
• They can contain the C-like escape sequences `\a' (bell), `\b' (backspace), `\f' (form feed), `\n' (newline), `\r' (carriage return), `\t' (horizontal tab), `\v' (vertical tab), `\\' (backslash), `\"' (double quote), `\'' (single quote), and `\newline' (that is, a backslash followed by a real newline, which results in a newline in the string).
• A character in a string may also be specified by its numerical value, through the escape sequence `\ddd', where ddd is a sequence of up to three decimal digits. Strings in Lua may contain any 8-bit value, including embedded zeros, which can be specified as `\000'

Numerical constants

• May be written with an optional decimal part and an optional decimal exponent.
• Examples: 3    3.0    3.1416    314.16e-2    0.31416E1

Control structures

• Three control structures are available, with the following syntax:

while expression do
         block
end
 
repeat
         block
until expression
 
if expression1 then
         block
elseif expression2 then
         block
else
         block
end

• In addition, when using a numeric index, the for construct is available:

for index = start, end, step do
         block
end

• step is optional; if absent, it is considered = 1; variable index is local to the loop; you can use a break statement to exit a for loop; in this case, assign index to another variable if you need it outside the loop.
• The condition expression of a control structure may return any value.All values different from nil are considered true; only nil is considered false.
• The return statement is used to return values from a function or from a chunk. Functions or chunks may return more than one value; the syntax for the return statement is
• return expression1 [expression2] (note that there are no brackets).
• The break statement can be used to terminate the execution of a loop, skipping to the next statement after the loop.
• A break ends the innermost enclosing loop (while, repeat, or for).
• For syntactic reasons, return and break statements can only be written as the last statements of a block.
• Use the structure do return end to insert a return in the middle of a block