Remove information on basic Lua programming, link to PiL
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@ -13,14 +13,10 @@ In this chapter we'll talk about scripting in Lua, the tools required
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to assist with this, and some techniques which you may find useful.
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- [Programming](#programming)
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- [Coding in Lua](#coding-in-lua)
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- [Code Editors](#code-editors)
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- [Coding in Lua](#coding-in-lua)
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- [Program Flow](#program-flow)
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- [Variable Types](#variable-types)
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- [Arithmetic Operators](#arithmetic-operators)
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- [Selection](#selection)
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- [Logical Operators](#logical-operators)
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- [Local and Global Scope](#local-and-global-scope)
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- [Locals should be used as much as possible](#locals-should-be-used-as-much-as-possible)
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- [Including other Lua Scripts](#including-other-lua-scripts)
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@ -41,6 +37,13 @@ however, the following websites are quite useful in developing this:
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* [Programming with Mosh](https://www.youtube.com/user/programmingwithmosh) is
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a good YouTube series to learn programming.
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### Coding in Lua
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It's also beyond the scope of this book to teach Lua coding.
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The [Programming in Lua](https://www.lua.org/pil/contents.html) book is an
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excellent introduction to Lua programming.
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## Code Editors
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A code editor with code highlighting is sufficient for writing scripts in Lua.
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@ -79,128 +82,6 @@ Commonly used editors which are well-suited for Lua include:
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Other suitable editors are also available.
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## Coding in Lua
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### Program Flow
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Programs are a series of commands that run one after another. We call these
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commands "statements." Program flow is how these statements are executed, and
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different types of flow allow you to skip or jump over sets of commands.
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There are three main types of flow:
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* Sequence: runs one statement after another, with no skipping.
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* Selection: skips over sequences depending on conditions.
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* Iteration: repeats the same statements until a condition is met.
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So, what do statements in Lua look like?
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```lua
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local a = 2 -- Set 'a' to 2
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local b = 2 -- Set 'b' to 2
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local result = a + b -- Set 'result' to a + b, which is 4
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a = a + 10
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print("Sum is "..result)
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```
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In this example, `a`, `b`, and `result` are *variables*. Local variables are
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declared by using the `local` keyword, and then given an initial value. Local
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will be discussed later, because it's part of a very important concept called
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*scope*.
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The `=` sign means *assignment*, so `result = a + b` means set the value of
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`result` to the value of `a + b`. Variable names can be longer than one
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character, as seen with the `result` variable. It's also worth noting that, like
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most languages, Lua is *case-sensitive*; `A` is a different variable to `a`.
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### Variable Types
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A variable will be only one of the following types and can change type after an
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assignment.
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It's good practice to make sure a variable is only ever nil or a single non-nil type.
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| Type | Description | Example |
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|----------|---------------------------------|----------------|
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| Nil | Not initialised. The variable is empty, it has no value | `local A`, `D = nil` |
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| Number | A whole or decimal number. | `local A = 4` |
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| String | A piece of text. | `local D = "one two three"` |
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| Boolean | True or False. | `local is_true = false`, `local E = (1 == 1)` |
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| Table | Lists. | Explained below. |
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| Function | Can run. May require inputs and may return a value. | `local result = func(1, 2, 3)` |
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### Arithmetic Operators
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Operators in Lua include:
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| Symbol | Purpose | Example |
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|--------|----------------|---------------------------|
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| A + B | Addition | 2 + 2 = 4 |
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| A - B | Subtraction | 2 - 10 = -8 |
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| A * B | Multiplication | 2 * 2 = 4 |
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| A / B | Division | 100 / 50 = 2 |
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| A ^ B | Powers | 2 ^ 2 = 2<sup>2</sup> = 4 |
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| A .. B | Join strings | "foo" .. "bar" = "foobar" |
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Please note that this is not an exhaustive list; it doesn't contain every
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possible operator.
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### Selection
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The most basic method of selection is the if statement. For example:
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```lua
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local random_number = math.random(1, 100) -- Between 1 and 100.
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if random_number > 50 then
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print("Woohoo!")
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else
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print("No!")
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end
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```
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This generates a random number between 1 and 100. It then prints "Woohoo!" if
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that number is bigger than 50, and otherwise prints "No!".
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### Logical Operators
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Logical operators in Lua include:
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| Symbol | Purpose | Example |
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|---------|--------------------------------------|-------------------------------------------------------------|
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| A == B | Equals | 1 == 1 (true), 1 == 2 (false) |
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| A ~= B | Doesn't equal | 1 ~= 1 (false), 1 ~= 2 (true) |
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| A > B | Greater than | 5 > 2 (true), 1 > 2 (false), 1 > 1 (false) |
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| A < B | Less than | 1 < 3 (true), 3 < 1 (false), 1 < 1 (false) |
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| A >= B | Greater than or equals | 5 >= 5 (true), 5 >= 3 (true), 5 >= 6 (false) |
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| A <= B | Less than or equals | 3 <= 6 (true), 3 <= 3 (true) |
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| A and B | And (both must be correct) | (2 > 1) and (1 == 1) (true), (2 > 3) and (1 == 1) (false) |
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| A or B | either or. One or both must be true. | (2 > 1) or (1 == 2) (true), (2 > 4) or (1 == 3) (false) |
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| not A | not true | not (1 == 2) (true), not (1 == 1) (false) |
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Please note that this doesn't contain every possible operator.
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It is also possible to combine operators. For example:
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```lua
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if not A and B then
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print("Yay!")
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end
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```
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This prints "Yay!" if A is false and B is true.
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Logical and arithmetic operators work the same way; they both accept inputs and
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return a value which can be stored. For example:
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```lua
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local A = 5
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local is_equal = (A == 5)
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if is_equal then
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print("Is equal!")
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end
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```
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## Local and Global Scope
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@ -239,6 +120,9 @@ one()
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two()
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```
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### Locals should be used as much as possible
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Local variables should be used whenever possible. Mods should only create one
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global at most, with the same name as the mod. Creating other globals is sloppy
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coding, and Minetest will warn about this:
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