diff --git a/_en/basics/lua.md b/_en/basics/lua.md index 1be8486..eba6a30 100644 --- a/_en/basics/lua.md +++ b/_en/basics/lua.md @@ -9,8 +9,8 @@ redirect_from: /en/chapters/lua.html ## Introduction -In this chapter we will talk about scripting in Lua, the tools required, -and go over some techniques which you will probably find useful. +In this chapter we'll talk about scripting in Lua, the tools required +to assist with this, and some techniques which you may find useful. - [Code Editors](#code-editors) - [Coding in Lua](#coding-in-lua) @@ -27,8 +27,11 @@ and go over some techniques which you will probably find useful. ## Code Editors A code editor with code highlighting is sufficient for writing scripts in Lua. -Code highlighting gives different colours to different words and characters -depending on what they mean. This allows you to spot mistakes. +Code highlighting uses different colours for words and characters +depending on what they represent. This allows you to easily notice +mistakes and inconsistencies. + +For example: ```lua function ctf.post(team,msg) @@ -46,30 +49,32 @@ function ctf.post(team,msg) end ``` -For example, keywords in the above snippet are highlighted such as if, then, end, and return. -table.insert is a function which comes with Lua by default. +Keywords in this example are highlighted, including `if`, `then`, `end`, and `return`. +Functions which come with Lua by default, such as `table.insert`, are also highlighted. -Here is a list of common editors well suited for Lua. -Other editors are available, of course. +Commonly used editors which are well-suited for Lua include: -* Windows: [Notepad++](http://notepad-plus-plus.org/), [Atom](http://atom.io/), [VS Code](https://code.visualstudio.com/) -* Linux: Kate, Gedit, [Atom](http://atom.io/), [VS Code](https://code.visualstudio.com/) -* OSX: [Atom](http://atom.io/), [VS Code](https://code.visualstudio.com/) +* [VSCode](https://code.visualstudio.com/) - + open source (as Code-OSS or VSCodium), popular, and has + [plugins for Minetest modding](https://marketplace.visualstudio.com/items?itemName=GreenXenith.minetest-tools). +* [Notepad++](http://notepad-plus-plus.org/) - Windows-only +* [Atom](http://atom.io/) + +Other suitable editors are also available. ## Coding in Lua ### Program Flow -Programs are a series of commands that run one after another. -We call these commands "statements." -Program flow is how these statements are executed. -Different types of flow allow you to skip or jump over sets of commands. +Programs are a series of commands that run one after another. We call these +commands "statements." Program flow is how these statements are executed, and +different types of flow allow you to skip or jump over sets of commands. + There are three main types of flow: -* Sequence: Just run one statement after another, no skipping. -* Selection: Skip over sequences depending on conditions. -* Iteration: Repeating, looping. Keep running the same - statements until a condition is met. +* Sequence: runs one statement after another, with no skipping. +* Selection: skips over sequences depending on conditions. +* Iteration: repeats the same statements until a condition is met. So, what do statements in Lua look like? @@ -81,16 +86,21 @@ a = a + 10 print("Sum is "..result) ``` -Whoa, what happened there? - -a, b, and result are *variables*. Local variables are declared -by using the local keyword, and then given an initial value. -Local will be discussed in a bit, as it's part of a very important concept called +In this example, `a`, `b`, and `result` are *variables*. Local variables are +declared by using the `local` keyword, and then given an initial value. Local +will be discussed later, because it's part of a very important concept called *scope*. The `=` means *assignment*, so `result = a + b` means set "result" to a + b. -Variable names can be longer than one character unlike in mathematics, as seen with the "result" variable. -It's also worth noting that Lua is *case-sensitive*; A is a different variable to a. +Variable names can be longer than one character unlike in mathematics, as seen +with the "result" variable. It's also worth noting that Lua is *case-sensitive*; +A is a different variable to a. + +The `=` sign means *assignment*, so `result = a + b` means set the value of +`result` to the value of `a + b`. Variable names can be longer than one +character, as seen with the `result` variable. It's also worth noting that, like +most languages, Lua is *case-sensitive*; `A` is a different variable to `a`. + ### Variable Types @@ -102,14 +112,14 @@ It's good practice to make sure a variable is only ever nil or a single non-nil |----------|---------------------------------|----------------| | Nil | Not initialised. The variable is empty, it has no value | `local A`, `D = nil` | | Number | A whole or decimal number. | `local A = 4` | -| String | A piece of text | `local D = "one two three"` | -| Boolean | True or False | `local is_true = false`, `local E = (1 == 1)` | -| Table | Lists | Explained below | -| Function | Can run. May require inputs and may return a value | `local result = func(1, 2, 3)` | +| String | A piece of text. | `local D = "one two three"` | +| Boolean | True or False. | `local is_true = false`, `local E = (1 == 1)` | +| Table | Lists. | Explained below. | +| Function | Can run. May require inputs and may return a value. | `local result = func(1, 2, 3)` | ### Arithmetic Operators -Not an exhaustive list. Doesn't contain every possible operator. +Operators in Lua include: | Symbol | Purpose | Example | |--------|----------------|---------------------------| @@ -120,9 +130,12 @@ Not an exhaustive list. Doesn't contain every possible operator. | A ^ B | Powers | 2 ^ 2 = 22 = 4 | | A .. B | Join strings | "foo" .. "bar" = "foobar" | +Please note that this is not an exhaustive list; it doesn't contain every +possible operator. + ### Selection -The most basic selection is the if statement. It looks like this: +The most basic method of selection is the if statement. For example: ```lua local random_number = math.random(1, 100) -- Between 1 and 100. @@ -133,12 +146,14 @@ else end ``` -That example generates a random number between 1 and 100. It then prints -"Woohoo!" if that number is bigger than 50, otherwise it prints "No!". -What else can you get apart from '>'? +This generates a random number between 1 and 100. It then prints "Woohoo!" if +that number is bigger than 50, and otherwise prints "No!". + ### Logical Operators +Logical operators in Lua include: + | Symbol | Purpose | Example | |---------|--------------------------------------|-------------------------------------------------------------| | A == B | Equals | 1 == 1 (true), 1 == 2 (false) | @@ -151,7 +166,9 @@ What else can you get apart from '>'? | A or B | either or. One or both must be true. | (2 > 1) or (1 == 2) (true), (2 > 4) or (1 == 3) (false) | | not A | not true | not (1 == 2) (true), not (1 == 1) (false) | -That doesn't contain every possible operator, and you can combine operators like this: +Please note that this doesn't contain every possible operator. + +It is also possible to combine operators. For example: ```lua if not A and B then @@ -159,10 +176,10 @@ if not A and B then end ``` -Which prints "Yay!" if A is false and B is true. +This prints "Yay!" if A is false and B is true. -Logical and arithmetic operators work exactly the same; -they both accept inputs and return a value which can be stored. +Logical and arithmetic operators work the same way; they both accept inputs and +return a value which can be stored. For example: ```lua local A = 5 @@ -175,22 +192,23 @@ end ## Programming Programming is the action of taking a problem, such as sorting a list -of items, and then turning it into steps that a computer can understand. +of items, and turning it into steps that a computer can understand. Teaching you the logical process of programming is beyond the scope of this book; however, the following websites are quite useful in developing this: * [Codecademy](http://www.codecademy.com/) is one of the best resources for - learning to 'code', it provides an interactive tutorial experience. -* [Scratch](https://scratch.mit.edu) is a good resource when starting from - absolute basics, learning the problem-solving techniques required to program.\\ - Scratch is **designed to teach children** how to program and isn't a serious + learning to write code. It provides an interactive tutorial experience. +* [Scratch](https://scratch.mit.edu) is a good resource for starting from + absolute basics, and learning the problem-solving techniques required to program.\\ + Scratch is *designed to teach children* how to program and isn't a serious programming language. ## Local and Global Scope -Whether a variable is local or global determines where it can be written to or read to. -A local variable is only accessible from where it is defined. Here are some examples: +Whether a variable is local or global determines where it can be written to or +read from. A local variable is only accessible from where it is defined. Here +are some examples: ```lua -- Accessible from within this script file @@ -207,25 +225,8 @@ function myfunc() end ``` -Whereas global variables can be accessed from anywhere in the script file, and from any other mod. - -```lua -my_global_variable = "blah" - -function one() - my_global_variable = "three" -end - -print(my_global_variable) -- Output: "blah" -one() -print(my_global_variable) -- Output: "three" -``` - - -### Locals should be used as much as possible - -Lua is global by default (unlike most other programming languages). -Local variables must be identified as such. +In contrast, global variables can be accessed from anywhere in the script file, and +from any other mod. ```lua function one() @@ -240,11 +241,9 @@ one() two() ``` -dump() is a function that can turn any variable into a string so the programmer can -see what it is. The foo variable will be printed as "bar", including the quotes -which show it is a string. - -This is sloppy coding and Minetest will, in fact, warn about this: +Local variables should be used whenever possible. Mods should only create one +global at most, with the same name as the mod. Creating other globals is sloppy +coding, and Minetest will warn about this: Assignment to undeclared global 'foo' inside function at init.lua:2 @@ -263,12 +262,11 @@ one() two() ``` -Remember that nil means **not initialised**. -The variable hasn't been assigned a value yet, -doesn't exist, or has been uninitialised (ie: set to nil). +Remember that nil means **not initialised**. The variable hasn't been assigned a +value yet, doesn't exist, or has been uninitialised (meaning set to nil). -The same goes for functions. Functions are variables of a special type, and -should be made local, as other mods could have functions of the same name. +Functions are variables of a special type, but should also be made local, +because other mods could have functions with the same names. ```lua local function foo(bar) @@ -276,7 +274,9 @@ local function foo(bar) end ``` -API tables should be used to allow other mods to call the functions, like so: +To allow mods to call you functions, you should create a table with the same +name as the mod and add your function to it. This table is often called an API +table or namespace. ```lua mymod = {} @@ -308,6 +308,5 @@ local ret = dofile(minetest.get_modpath("modname") .. "/script.lua") print(ret) -- Hello world! ``` -Later chapters will discuss how to split up the code of a mod in a lot of detail. -However, the simplistic approach for now is to have different files for different -types of things - nodes.lua, crafts.lua, craftitems.lua, etc. +[Later chapters](../quality/clean_arch.html) will discuss how best to split up +code for a mod.