# Intrinsics First, let me define what I mean when I say "intrinsic". I am referring to anything that is available to Cosmo without having to install a package. For example: the `puts` and `gets` functions are global intrinsics, and the `HTTP` and `System` libraries are imported intrinsics. ## Written in Cosmo If you want to write any code in Cosmo that will be intrinsic to Cosmo, just create a new Cosmo file in [`libraries/`](https://github.com/cosmo-lang/cosmo/tree/master/libraries) and code away. Each file in `libraries/` becomes an importable, except for `global.⭐`, which is injected into the global scope. When creating an importable intrinsic in Cosmo, the name to import will be the file name without the extension. For example: if I created `libraries/colors.⭐`, it would be importable via `colors`. ```sql use * from "colors" ``` ## Written in Crystal If you want to define Cosmo intrinsics that rely on Crystal to run (or are performance intensive), you can refer to [`src/cosmo/runtime/intrinsic`](https://github.com/cosmo-lang/cosmo/tree/master/src/cosmo/runtime/intrinsic). There are two types of intrinsics you can create via Cosmo's Crystal API: [`Lib`](https://cosmo-lang.github.io/cosmo/Cosmo/Intrinsic/Lib.html)s, and [`IFunction`](https://cosmo-lang.github.io/cosmo/Cosmo/Intrinsic/IFunction.html)s. ### Intrinsic::Lib A `Lib` is just a table behind the scenes, and holds associated `IFunction`s or other values. It contains an `inject` method which assigns any associated values into the scope.

The FileLib#inject method

As you can see, it defines a hash called `file` and assigns all of the `File` library's functions into it. It then assigns the `file` hash to the name `File` in the scope. ### Intrinsic::IFunction An `IFunction` is just a regular function, just without a body node. They are called like normal functions, besides having to interpret the function body. Arity checks are done just like normal functions as well. The below example of an `IFunction` (taken from `Math::atan`) has an arity of 1, meaning that it will throw if any more or any less arguments are provided. It also uses the [`TypeChecker#assert`](https://cosmo-lang.github.io/cosmo/Cosmo/TypeChecker.html#assert%28typedef%3AString%2Cvalue%3AValueType%2Ctoken%3AToken%29%3ANil-instance-method) method to make sure the input is a float or an integer.
### Declaring/Importing Intrinsics written in Cosmo are **not** importable **OR** in the global scope by default. To finally implement your intrinsic, navigate to the [`Interpreter#declare_globals`](https://github.com/cosmo-lang/cosmo/blob/c87d84797940a6ff3a956657a6fed04ab49d203d/src/cosmo/runtime/interpreter.cr#L43) method. Each call to `declare_intrinsic` declares it as global. To make it importable, call the `importable` method. The first argument to the `importable` method is the name that it will be importable by. So for example, importing `MathLib` would look like: ```sql use sin, cos, π from "math" ```