Toy/using-toy.md

# Using Toy

This tutorial assumes that you've managed to embed Toy into your program by following the tutorial [Embedding Toy](embedding-toy).

Here, we'll look at some ways in which you can utilize Toy's C API within your host program.

Be aware that when you create a new Literal object, you must call `freeLiteral()` on it afterwards! If you don't, your program will leak memory as Toy has no internal tracker for such things.

## Embedded API Macros

The functions intended for usage by the API are prepended with the C macro `TOY_API`. The exact value of this macro can vary by platform, or even be empty. In addition, the macros defined in [literal.h](https://github.com/Ratstail91/Toy/blob/0.6.0/source/literal.h) are available for use when manipulating literals. These include:

* `IS_*` - check if a literal is a specific type
* `AS_*` - cast the literal to a specific type
* `TO_*` - create a literal of a specific type
* `IS_TRUTHY` - check if a literal is truthy
* `MAX_STRING_LENGTH` - the maximum length of a string in Toy (can be altered if needed)

## Structures Used Throughout Toy

The main unit of data within Toy's internals is `Literal`, which can contain any value that can exist within the Toy langauge. The exact implementation of `Literal` may change or evolve as time goes on, so it's recommended that you only interact with literals directly by using the macros and functions outlined [above](#embedded-api-macros). See the [types](types) page for information on what datatypes exist in Toy.

There are two main "compound structures" used within Toy's internals - the `LiteralArray` and `LiteralDictionary`. The former is an array of `Literal` instances stored sequentially in memory for fast lookups, while the latter is a key-value hashmap designed for efficient lookups based on a `Literal` key. These are both accessible via the language as well.

These compound structures hold **copies** of literals given to them, rather than taking ownership of existing literals.

## Compiling Toy Scripts

Please see [Compiling Toy](compiling-toy) for more information on the process of turning scripts into bytecode.

## Interpreting Toy

The `Interpreter` structure is the beating heart of Toy - You'll usually only need one interpreter, as it can be reset as needed.

The four basic functions are used as follows:

```c
//assume "tb" and "size" are the results of compilation
Interpreter interpreter;

initInterpreter(&interpreter);
runInterpreter(&interpreter, tb, size);
resetInterpreter(&interpreter); //You usually want to reset between runs
freeInterpreter(&interpreter);
```

In addition to this, you might also wish to "inject" a series of usable libraries into the interpreter, which can be `import`-ed within the language itself. This process only needs to be done once, after initialization, but before the first run.

```c
injectNativeHook(&interpreter, "standard", hookStandard);
```

A "hook" is a callback function which is invoked when the given library is imported. `standard` is the most commonly used library available.

```
import standard;
```

Hooks can simply inject native functions into the current scope, or they can do other, more esoteric things (though this is not recommended).

```c
//a utility structure for storing the native C functions
typedef struct Natives {
	char* name;
	NativeFn fn;
} Natives;

int hookStandard(Interpreter* interpreter, Literal identifier, Literal alias) {
	//the list of available native C functions that can be called from Toy
	Natives natives[] = {
		{"clock", nativeClock},
		{NULL, NULL}
	};

	//inject each native C functions into the current scope
	for (int i = 0; natives[i].name; i++) {
		injectNativeFn(interpreter, natives[i].name, natives[i].fn);
	}

	return 0;
}
```

## Calling Toy from C

In some situations, you may find it convenient to call a function written in Toy from the host program. For this, a pair of utility functions have been provided:

```c
TOY_API bool callLiteralFn(Interpreter* interpreter, Literal func, LiteralArray* arguments, LiteralArray* returns);
TOY_API bool callFn       (Interpreter* interpreter, char* name,   LiteralArray* arguments, LiteralArray* returns);
```

The first argument must be an interpreter. The third argument is a pointer to a `LiteralArray` containing a list of arguments to pass to the function, and the fourth is a pointer to a `LiteralArray` where the return values can be stored (an array is used here for a potential future feature). The contents of the argument array is consumed and left in an indeterminate state (but is safe to free), while the returns array always has one value - if the function did not return a value, then it contains a `null` literal.

The second arguments to these functions are either the function to be called as a `Literal`, or the name of the function within the interpreter's scope. The latter API simply finds the specified `Literal` if it exists and calls the former. As with most APIs, these return `false` if something went wrong.