Lua Language Introduction

Identifiers and Variables

Lua supports identifiers starting with English letters and underscores as variable or function names.

Lebai's Lua interpreter extends this rule, supporting UTF-8 characters as identifiers.

In Lua, global variables can be used without declaration, defaulting to nil, with no quantity limit. To use local variables, add local before the declaration statement. Up to 200 local variables can be declared. Both local and global variables are garbage collected after program execution completes.

The following statements are all valid in Lebai robots:

local a = 0
b = a
_test = {}
variable = b

Comments

Single-line comments start with --:

-- I am a comment

Multi-line comments use two brackets [[ ]] after --:

--[[
    Multi-line comment
    Second line
--]]

To uncomment, add a - before --[[:

---[[
    a = 0
    b = a + 1
--]]

Types and Values

Lua is a dynamically typed language, you can use the type() function to get the type. Lua has 8 basic types:

1. nil type(nil) --> nil
2. boolean type(true) --> boolean
3. number type(10.4 * 3) --> number
4. string type("hello world") --> string
5. userdata type(io.stdin) --> userdata
6. function type(print) --> function
7. table type({}) --> table
8. thread

Undeclared global variables are nil, assigning nil to a variable deletes it.

In Lua, conditional tests treat all values except false and nil as true. Supports binary operators and and or, and unary operator not.

Common variable initialization:

count = (count or 0) + 1

Equivalent to:

if not count then
    count = 0
end
count = count + 1

Numbers

In Lua 5.2, the number type does not distinguish between integers and floats, both represented in double-precision floating-point format.

Lua 5.3 starts supporting integer types.

Number Constants

Decimal and scientific notation:

assert(1 == 1.0)
assert(-3 == -3.0)
assert(0.2e3 == 200)
assert(4.57e-3 == 0.00457)

Hexadecimal and formatting:

assert(0xff == 255)
assert(0x1A3 == 419)
assert(0x0.2 == 0.125)
assert(0x1p-1 == 0.5)
assert(0xa.bp2 == 42.75)
string.format("%a", 419) -- 0x1.a3p+8
string.format("%a", 0.1) -- 0x1.999999999999ap-4

Operations and Math Library

Arithmetic operations:

assert(13 + 15 == 28) -- Addition
assert(13.0 + 25 == 38.0) -- Addition
assert(-(3 * 6.0) == -18.0) -- Subtraction, multiplication, negation
assert(3 / 2 == 1.5) -- Division
assert(3 // 2 == 1) -- Floor division (Lua 5.3)
assert(3 % 2 == 1) -- Modulo
assert(2 ^ 3 == 8) -- Power

Relational operations:

assert(1 + 1 == 2) -- Equal
assert(1 + 1 ~= 3) -- Not equal
assert(1 < 3) -- Less than
assert(1 <= 3) -- Less than or equal
assert(3 > 1) -- Greater than
assert(3 >= 1) -- Greater than or equal

Random number generation:

math.randomseed(os.time()) -- Set random seed
print(math.random()) -- Generate random number in [0,1)
print(math.random(6)) -- Generate random number in [1,6]
print(math.random(10, 20)) -- Generate random number in [10, 20]

Rounding functions:

assert(math.floor(3.3) == 3) -- Floor
assert(math.ceil(3.3) == 4) -- Ceil
a, b = math.modf(3.5) -- Round toward zero
assert(a == 3 and b == 0.5)

Angle and trigonometric functions:

deg = 30
rad = math.rad(deg) -- Degrees to radians
print(math.deg(rad)) -- Radians to degrees

sin = math.sin(rad) -- Sine
print(math.asin(sin)) -- Arc sine

cos = math.cos(rad) -- Cosine
print(math.acos(cos)) -- Arc cosine

tan = math.tan(rad) -- Tangent
print(math.atan(tan)) -- Arc tangent

Other math functions:

assert(math.abs(-1) == 1) -- Absolute value
assert(math.min(1, 2, 3) == 1) -- Minimum
assert(math.max(1, 2, 3) == 3) -- Maximum

assert(math.sqrt(4) == 4^0.5) -- Square root
print(math.exp(10)) -- e^10
print(math.log(10)) -- Natural logarithm
print(math.log(10, 2)) -- Logarithm base 2

Math constants:

print(math.pi) -- Pi
print(math.huge) -- Infinity

Error Handling

When an error occurs, if not caught and handled, the task will exit abnormally.

To handle errors in Lua, use the pcall (protected call) function to wrap the code to be executed.

Syntax:

success, result1, result2, ... = pcall(function, arg1, arg2, ...)

Example:

function divide(a, b)
    if b == 0 then
        error("Cannot divide by zero")
    end
    return a / b
end

success, result = pcall(divide, 10, 0)
if not success then
    print("Error occurred: ", result)
else
    print("Result: ", result)
end