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Pico-8

Pico-8 lua is not standard

• it has some addition (+=, if() oneline, ..)
  • all, add - some which can be emulated on standard lua

• it lack some standard fonction (string.*n table.*) which may exist (or not in a different form).

• z8lua / github - a fork of Lua that implements the PICO-8 dialect.
  • to install: git clone + make => z8lua binary
  • does not support require? as such difficult to use for unit-testing - though It should be possible to patch it to support require 🚧
• Going from Lua 5.2 to PICO-8’s Lua

Lua Langage

Setup

$ sudo apt install lua5.2   # this is the closest to PICO-8 v0.2.5g

Table

Table can be treated as an array (list-like) or as a key-value dictionary.

-- Array
t = {1, 2, 3}

-- of dictionnary: Simple object-like table
Person = {
    name = "Alice",
    age = 25
}

Appending to a table

-- Array
table.insert(t, 4)  -- use add() in pico8

-- or assign to next index
t[#t + 1] = 5

for i, v in ipairs(t) do
    print(i, v)
end

-- for dictionnary just assign the key
Person["c"] = 3
Person.d = 4  -- shorthand for t["d"]

for k, v in pairs(Person) do
    print(k, v)
end

Removing Element

tables don’t have a fixed “remove” operator, but PICO-8 provides two handy functions:

Remove by value → del(tbl, value) This removes the first occurrence of the given value.

t = {10, 20, 30, 20}

del(t, 20)   -- removes the first 20
-- t = {10, 30, 20}

Remove by index → deli(tbl, index) This removes the element at a specific position.

t = {10, 20, 30, 40}

deli(t, 2)  -- removes element at index 2
-- t = {10, 30, 40}

Notes Both del() and deli() automatically shift later elements down so there are no gaps.

If the value isn’t found (for del) or the index is out of range (for deli), nothing happens.

Enum

Lua doesn’t have built-in enums like C, C#, or Java.

The closest to a C-style enum is simple table constants:

local Colors = {
    RED = 1,
    GREEN = 2,
    BLUE = 3
}

print(Colors.RED)   -- 1

static

Do not exist, see discussion

Currying

• Function currying for fun and….fun

Object / Struct

see Meta-table

Operators

== equal to
~= not equal to, Pico-8 support != as well
< less than
> greater than
<= less than or equal to
>= greater than or equal to

Unit Testing

• Popular Lua Testing Frameworks

busted

The most widely used Lua test framework.

Syntax could be lighten with Moonscript. 🚧

Setup

$ sudo apt-get install luarocks
$ sudo apt install liblua5.2-dev  # depending on lua -v
$ sudo luarocks install busted
$ busted --version # validate

Example

describe("math", function()
  it("adds numbers correctly", function()
    assert.is_equal(4, 2 + 2)
  end)
end)

Then run with

$ busted . # By default, it looks for *_spec.lua files in your project.

VSCode 🚧

see Busted Test Explorer by Vivien Henriet

Busted error: spawn /usr/local/bin/busted ENOENT
Busted exited with code -2

see also

• LuaRocks - the package manager for Lua modules.
• Piccolo – A Stackless Lua Interpreter / HN
• Lux / HN - a luxurious package manager for Lua