# Q&

## About

A single-pass byte code interpreter with the ability to pre-compile executables
into a format that can be efficiently executed by the runtime.
It serves many features, which are listed a bit further down below.

This would have officially been the fourth iteration of my language (sqript4),
but I thought I'd stop with the numbers as people would ask what happened to the
previous three languages.

Q& (or Qamp for Q Ampersand) was originally made for my contributions to the 
Advent Of Code 2025, but I thought it's a nice and stable enough concept to be
sharing it to the public anyway.

## Usage

To build **Q&**, you need nothing more than a C# compiler that supports .NET10.
There are .NET8 compatible versions available, but they are not recommended,
as **Q&** utilizes all of the performance optimizations .NET10 has to offer.

After cloning, a simple `dotnet build ./` in the root directory will suffice.

You can execute pre-compiled .sqi files using `qamp.runtime.exe <filepath> [parameters]`,
or the REPL/CLI using `qamp.cli.exe [parameters]`.
If you want to build your own source into pre-compiled instruction files,
use `qamp.digest.exe <dirpath>` - the digester will look for an `Init()` function
declared in any of the files, and build the instructions from there.

## Language & Syntax

You are free to choose between the classic sqript-style dialect `*~ q <~ 0xf;` or
the standard dialect, which is strongly inspired by the C# standard: `var q = 0xf;`.

All of the following examples are written in the classic dialect `--dialect=sqr` or `-d=q`.

### Syntax

Most basic Usage:
```cs
                                            # this is a comment.
*~ q <~ 12;                                 # q == 12
*~ f <~ (n) <: n < 2 ? n : f(n-1) + f(n-2); # fibonacci
f(12);                                      # 233
*~ a <~ [1, 2, 3];                          # a = [1, 2, 3]
*~ x <~ a:0 + a:2;                          # x == 4
```

### Assignments

**Q&** has two distinct ways to assign a value to a variable: 
 - By reference `<&`, or 
 - By value `<=`.

Using the auto-assignment operator `<~`, **Q&** will choose the correct assignment based on what
type the right-hand expression consists of.
Primitive types will be assigned by value, any object values will be assigned by reference.
This is strongly inspired by the behaviour that most interpeters implement.

#### What happens if...
##### I assign an object by value?
The entire object will be deep-copied and transfered to the new location.
See it as a free clone method on basically anything that is considered an object.
##### I assign a primitive by reference?
So, assuming that `x` is a primitive (value type), given the instruction `*~ y <& x;`,
`y` will be assigned as a reference value _pointing_ to the location of `x` - somewhat like a
pointer in C, but a little smarter.
##### I do not praise the god emperor of mankind?
You will be duly punished.

#### Variable Declaration

```
*~ q <~ 0xf;
```

#### Variable Declaration

## Customization & Extras

Some more information about extending and customizing Q& to your needs.

### Implementing external Libraries

Implementation is easy.
Q& is written in C#, and supports basically anything you can wrap in C#.
All you have to do in order to implement a library is referencing the SDK dll
which should be located within your `./Build/` folder after building as described above.

Here's a quick example of how you would implement virtually any library:
```cs
using Qrakhen.Qamp.Core;

// This is an intentionally bad implementation of a linked list.
[ExportType("llist")]
public class LinkedListNode : Obj
{
   [HideProperty]
   public LinkedListNode? Next { get; private set; }   

   public Value Value { get; private set; }  

   public LinkedList(Value value) {
      // ...internal setup
      this.Value = value;
   }

   // Q& constructors, if needed, have to be explicitely declared to return a value type.
   [ExportConstructor]
   public static Value Ctor(params Value[] args) {
      current = this;
      while (current.Next != null)
         current = current.Next;
     
      // This simply returns a new pointer to an already existing
      // oject inside the heap, rather than actually create a new one.
      // It wraps a pointer to the provided object inside a value that
      // has the 'Ptr' type flag, passing it to the Q& runtime.
      return Obj.Create(current);
   }

   // Tell the type mapper to export this method
   [ExportMethod]
   public Value Last() {
      // This simply returns a new pointer to an already existing type.
      // The call ddoes not actually create a new object.
      var current = this;
      while (current.Next != null) {
         current = current.Next;
      return Obj.Create();
   }

   // Value is the base type of anything in Q&.
   // An object is just a value of type 'Ptr' (value.IsPtr),
   // and primitives have their value stored in the 8 byte
   // buffer of the value itself (value.Data).
   [ExportMethod]
   public void Add(Value value) {
      var current = this;
      while (current.Next != null)
         current = current.Next;
      current.Next = new LinkedList(value);
   }

   // Methods that accept a primitive will automatically try 
   // retrieve that type from the provided arguments as Values.
   // You may always simply declare to accept Values aswell,
   // which gives you some dynamic flexibility if needed.
   [ExportMethod]
   public Value? GetItem(long index) {
      long current = 0;
		var node = this;
      while (current < index) {
	      current++;
	      node = node.Next;
      }
      return node;
   }
}
```

You may manually register all types inside an assembly by calling 
```
   Library:Load("mylib.dll");
```
directly in Q&.
Usage of the type described above would look somewhat like this:
```
   *~ list = new llist();
   list.Add(5);
   list.Add('test');
   list.Add([1, 2, 3]);
   print(list.GetItem(1));    // 'test'
   print(list.Last());        // [ 1, 2, 3 ]
   *~ protected = list.Value; // will throw an exception, as we did not expose that property.
```

That's it - although this being a very simple example, more is possible.
I will add a few basic implementations of very common libraries in a separate repository soon.