Quick Lua tutorial
By UZ
Saturday, February 14, 2004
This tutorial is by no means complete; it is provided as a simple helper when starting to learn Lua.
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
Assignments
-----------
Lua allows multiple assignments: list of variables on the left side, list of expressions on the right side.
The elements in both lists are separated by commas.
First, all values on the right side and eventual indices on the left side are evaluated, and then assignments are made.
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
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