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Lua crash course
Following crash course is an extremely condensed extract from the official Lua reference manual. For more details refer to the Lua website and to the numerous examples contained in the demo scenes.
Lexical conventions
Lua is a case sensitive language. "and", "And" or "AND" are not the same.
Following are Lua keywords:
and break do else elseif
end false for function if
in local nil not or
repeat return then true until while
Following strings denote other tokens:
+ - * / % ^ #
== ~= <= >= < > =
( ) { } [ ]
; : , . .. ...
Literal strings can be delimited by matching single or double quotes (e.g. 'hello' or "hello")
A comment starts with a double hyphen (--) anywhere outside of a string. e.g.:
a=4 -- variable a is now 4!
Types and values
Lua is a dynamically typed language which means that variables do not have types; only values do.
There are 8 basic types in Lua:
nil type of the value nil whose main property is to be different from any other value.
It usually represents the absence of a useful value
bool values false and true (both nil and false make a condition false;
any other value makes it true)
number both integer and floating-point numbers (has internally two distinct
representations: integer and float)
string arrays of characters (strings may contain any 8-bit character,
including embedded zeros)
function Lua functions
userdata can hold arbitrary C data (corresponds to a block of raw memory)
thread independent threads of execution used to implement coroutines
table arrays that can hold values of any type except nil
Variables
There are 3 kinds of variables: global variables, local variables and table fields. Any variable is assumed to be global unless explicitely declared as local
Before the first assignment to a variable, its value is nil
Square brackets are used to index a table (e.g. value=table[x]). The first value in a table is at position 1 (and not 0 as for C arrays)
Statements
Lua allows multiple assignments. The syntax for assignments 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:
x,y,z = myTable[1],myTable[2],myTable[3]
Relational operators (always result in false or true)
== equality
~= negation of equality
< smaller than
> bigger than
<= smaller or equal than
>= bigger or equal than
If control structure (by example):
if value1==value2 then
print('value1 and value2 are same!')
end
For control structure (by example):
for i=1,4,1 do -- count from 1 to 4 with increments of 1
print(i)
end
While control structure (by example):
i=0
while i~=4 do
i=i+1
end
Repeat control structure (by example):
i=0
repeat
i=i+1
until i==4
Table operations (by example):
myTable={'firstValue',2,3} -- builds a table with 3 values
print(myTable[1]) -- prints the first element in the table
table.insert(myTable,4) -- appends the number 4 to the table
Concatenation (by example):
a=' hello'
b=' world'
c=a..b -- c contains 'hello world'
Length operator #:
stringLength=#'hello world'
tableSize=#{1,2,3,4,5}
Bitwise operators
Lua supports the following bitwise operators:
&: bitwise AND
|: bitwise OR
~: bitwise exclusive OR
>>: right shift
<<: unary bitwise NOT
~: unary bitwise NOT
Coroutines or threads
Coroutines are easily created and resumed with:
-- Create a coroutine:
corout=coroutine.create(coroutineMain)
-- Start/resume a coroutine:
if coroutine.status(corout)~='dead' then
local ok,errorMsg=coroutine.resume(corout)
if errorMsg then
error(debug.traceback(corout,errorMsg),2)
end
end
-- The coroutine itself:
function coroutineMain()
while true do
-- some code
end
end
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