%% title = "Lua - a scripting language you can like"

% id = "01HRG2RJC1BATZJSGSSSF1XNFZ"
- TODO: this page could really use an interactive Lua interpreter. can we have that?

% id = "01HRG2RJC1J57MFVA0QFXP8WWW"
- Lua is a really cool language! did you know that?

% id = "01HRG2RJC1N1J4FTZ4M4MW72VZ"
- lots of people complain about it being really weird for various reasons, but these are generally superficial

    % id = "01HRG2RJC1637T8NPCWH90E5W0"
    - usually it's cosmetic stuff, so these aren't any arguments of technical merit, but…

    % id = "01HRG2RJC10G9GEGM5JCX32FE4"
    - stuff like indexing from 1 instead of 0, which is _just a design choice_ and does not impact your programming that much

        % id = "01HRG2RJC1MTW370DDEXQ0AN72"
        - in fact, one could argue that regular programmers are weird for counting from zero :thinking:

        % id = "01HRG2RJC1DH3WE4VGQCMEDN15"
        - the biggest impact this has is on rendering code, where you have to subtract 1 to position things relative to the origin - which is at `(0, 0)` (or `(0, 0, 0)` in 3D.)

    % id = "01HRG2RJC1VJ5FDDM8X9ECB3HR"
    - or using `~=` instead of `!=`, which is _just a syntax choice_, and you only have to get used to it once

    % id = "01HRG2RJC160QD16204NDAYTSW"
    - or using `do`..`end` style blocks instead of `{`..`}`, which again is _just a syntax choice_ and does not impact programming that much

        % id = "01HRG2RJC1D377M98MDT9BX8EQ"
        - it's a tad bit more line noise, but not that terrible. I [did design a language using `do`..`end` blocks][def:mica/repo] and it really doesn't look that bad

    % id = "01HRG3MJ0KRVRWEMRKX8TQFZAK"
    - TODO: this section could use some links to actual complaints or statistics or something. anecdotal evidence is not evidence.

% id = "01HRG2RJC1RTAJJ1MX2JZAMBW8"
- but I think Lua is a pretty damn genius programming language.

    % id = "01HRG2RJC11KMM8AVCSSQ96H26"
    - the use of tables as The One Data Structure for Literally Everything strikes me as a 200 IQ choice I could never come up with myself

        % id = "01HRG2RJC1SJSFQSR1X3TT638F"
        - partly because it's so fucking bold I can literally not imagine myself designing a language with a strong distinction between hash tables and arrays, and even tuples and records!
        but the designers of Lua had the restraint to just have One.

        % id = "01HRG2RJC13YK030EPGMKM9H8H"
        - tables are extremely powerful in what they can do, because they're more than just a way of structuring data - they also allow for interfacing with the language *syntax* through operator overloading

            % id = "01HRG2RJC1PDZFB2WBW7D827KF"
            + in fact object oriented programming in Lua is typically done by overloading the `[]` indexing operator.

                % id = "01HRG2RJC1HK3SG51X6DJFCD0B"
                - the way it works is that [`a.b` is just syntax sugar for `a["b"]`][branch:01HRG2RJC2PA5KE0DH0RRFGW9E], which means you overload `[]` to _fall back to another table_ - and that way you can achieve [prototype-based inheritance](https://en.wikipedia.org/wiki/Prototype-based_programming)!

                ```lua
                local fallback = { b = 2 }
                local base = { a = 1 }

                -- The __index field can be both a function *and* a table.
                -- { __index = the_table } is a shorthand for { __index = function (t, k) return the_table[k] end }
                setmetatable(base, { __index = fallback })
                assert(base.b == 2)
                ```

    % id = "01HRG2RJC23XH1053A69MQJD4N"
    - I'll be honest that I don't like the standard library of Lua from a usability standpoint, but maybe it *doesn't need to be bigger*.
    it's similar to the principles of [Go](https://go.dev/), where the language encourages using dumb constructs rather than super clever code with lots of abstraction.

        % id = "01HRG2RJC2P3832KTQMANBHGE6"
        - though unlike Go, Lua has the goal of being *small* because it needs to be *embeddable*, especially given it's used in very constrained environments in the real world. (microcontrollers!)

            % id = "01HRG2RJC2S3V38FM6DB0481WK"
            - therefore there are technical, not just ideological reasons to keep the library small.

        % id = "01HRG2RJC2KPZXH90Z6B92ZNB6"
        - and I really like that from an embedder's standpoint, it's possible to completely disable certain standard library modules for sandboxing!

    % id = "01HRG2RJC2W4MK96FMWRTS8QCJ"
    - Lua also knows *very* well how much syntax sugar to have to make writing code pleasant, but not to overdose it so much as to give you instant diabetes.

        % id = "01HRG2RJC28DT0TZT47WPABD65"
        + as an example, there's function call syntax: you can pass it a string or table *literal*, which is just enough to enable some really nice DSLs without making the grammar too complex.

            % id = "01HRG2RJC2CVKS9CFVQ9HJSBH4"
            - once upon a time I dreamed up a DSL for building GUIs using this sugar.

            ```lua
            render {
                width = 800, height = 600,
                title = "Hello, world!",

                vertical_box {
                    header1 "Hello, world!",
                    header2 "This is an example GUI.",
                }
            }
            ```

                % id = "01HRG2RJC2T7BF6XS3T7Q8AXW2"
                - ***JUST LOOK AT HOW CLEAN IT IS!*** with no need to [invent magic syntax](https://www.typescriptlang.org/docs/handbook/jsx.html) or anything!

                % id = "01HRG2RJC2D69JYCWQXSF2FQNY"
                - the only missing thing then would be list comprehensions to be able to transform data into GUI elements, but even that can be ironed over using function literals:

                ```lua
                render {
                    width = 800, height = 600,
                    title = "Hello, world!",

                    vertical_box {
                        header1 "Hello, world!",
                        paragraph "This is an example GUI. Here's a horizontal list of numbers:",

                        horizontal_box {
                            function (t)
                                for i = 1, 10 do
                                    t[i] = paragraph(tostring(i))
                                end
                            end,
                        }
                    }
                }
                ```

                interpret this code however you want, but *damn* it looks clean. again with no magic syntax!

        % id = "01HRG2RJC2PA5KE0DH0RRFGW9E"
        - there is also the incredibly useful sugar for indexing tables by string literals: instead of `table["x"]` you can write down `table.x`

            % id = "01HRG2RJC2WDXCPW12JDD4749R"
            + and there is also the incredibly useful method call sugar `table:func()`, which gets transformed to `table.func(table)`;
            and function definitions like `function table:func() end` are sugar for `function table.func(self) end`. ain't that neat and simple, yet super useful?

                % id = "01HRG2RJC23955SMQXHWEA202J"
                - if you don't get the usefulness: this is needed because object oriented methods in Lua are implemented using regular functions; there is no magic `this` or `self` parameter.
                the parameter is explicit, there is just sugar for passing it into functions and declaring functions with it.

% id = "01HRG2RJC2FF05JWQ6KHS4Y5WF"
- I really wish Lua had at least *a* form of static typing though, since knowing about errors you make early is _really_ helpful during development.

    % id = "01HRG2RJC2JP3HRTVMAQ22HDVE"
    + it regularly happened to me that a type error I made only occured at *some point* later during runtime; and then you have to track down a reproduction case and make a fix at the source. not fun.

        % id = "01HRG3MJ0KGZ8T4KHMV6KZXDK4"
        - there's also the ugly case I had with a division by zero in the last rewrite of [Planet Overgamma][def:planet_overgamma/repo], which caused a NaN to propagate through physics and into rendering, causing a crash.

            % id = "01HRG3MJ0KKMR7MDXST9PCYF6Q"
            - this is precisely where [my hate for NaN propagation][branch:01HPEMVAH9JZWYPVN53GVFQNQY] was born.

    % id = "01HRG2RJC224TNYEWGRBCTJA0S"
    - there's [Teal](https://github.com/teal-language/tl) but last time I checked it didn't have support for inheritance, which is heavily used by [LÖVE](https://love2d.org/), which is my go-to Lua graphics framework.

    % id = "01HRG2RJC2JS0JXFM23SWHKTFN"
    - you can also compile [TypeScript to Lua](https://typescripttolua.github.io/), which is insanely silly, but has the advantage of using a language that's more familiar to a very wide group of people.
    I wouldn't use it though because TypeScript and Lua are very different languages, and I'm afraid certain transforms would be unobvious - which would make interfacing with existing Lua code harder.
    I think I prefer the bolt-a-type-system-onto-Lua approach of Teal in that regard.

% id = "01HRG2RJC29C751N6A90G8RENK"
- and it's really a bummer that Lua is not that strict!

    % id = "01HRG2RJC2EGS11ERP93BY5BVK"
    - global variables by default are a pretty bad design choice in my opinion. having any form of uncontrolled globals hurts local reasoning and makes it harder to tell whatever your code is going to do.

        % id = "01HRG2RJC2VMCBATX88ZE7SYA0"
        - but fortunately it is possible to freeze your global variables by overloading the indexing operators of `_G` - the table that represents the global scope.

        ```lua
        setmetatable(_G, {
            __index = function (t, k)
                -- Only tell the programmer about undeclared variables. We still want access to
                -- builtins like `require`.
                if t[k] == nil then
                    -- The error message is purposefully generic because this will probably happen
                    -- the most when misspelling variables.
                    error("variable '"..k.."' was not declared in this scope")
                end
                return rawget(t, k)
            end
            __newindex = function (t, k, v)
                -- Assigning to global variables usually happens due to typos with local variables,
                -- so again - the error message is intentionally generic.
                error("variable '"..k.."' was not declared in this scope")
            end
        })
        ```

% id = "01HRG2RJC229JBT8YQFE3P1V8C"
- there are also some bits of syntax that arguably haven't aged very well.

    % id = "01HRG2RJC2N52T5X32YKPWP317"
    - as much as people [complain about cosmetics][branch:01HRG2RJC1VJ5FDDM8X9ECB3HR], I think there's a particular design choice that has aged very poorly in the face of modern, functional programming - function literals.

    these tend to be quite verbose in Lua which hurts readability in functional code:

    ```lua
    local u = map(t, function (v) return v + 2 end)
    ```

    compare that to JavaScript's arrow functions `=>`, which I think are a prime example of good syntax sugar that encourages more function-oriented programming:

    ```javascript
    let u = t.map(v => v + 2)
    ```

        % id = "01HRG2RJC2CS2MA98TTHK7MBQ9"
        - the lack of a pipelining operator `|>` is also an annoyance, albeit most modern imperative languages don't have it either.