## CrossLang Handbook

This is a book for my language found [here](https://crosslang.tesseslanguage.com/)

## Statements and loops



#### Declare a variable (it is an expression)

You can (the var is optional but should be used if the root environment has the same variable and you don't want to set it)

```js
var myVariable = 42;
```

#### Set a variable (it is an expression)

```js
myVariable = "I have set the variable to a string";
```

#### Reflective variables

```js
var nameOfVariable = "Var 1";
.[nameOfVariable] = 42; //the variable name in this instance will be Var 1
Console.WriteLine(.[nameOfVariable]); //prints 42


var nameOfVariable2 = "Var 2";
var nameOfField = "This field has spaces and \n New Lines";
.[nameOfVariable2] = {
    .[nameOfField] = "Hello, world"
};

Console.WriteLine(.[nameOfVariable2].[nameOfField]); //should print Hello, world

```


#### If statements

The {} are optional if you only need one statement

```js
var myExpression = 0; 
var myOtherExpression = {
    mol = 42
};

if(myExpression)
{
    Console.WriteLine("myExpression is truthy");
}
else if(myOtherExpression)
{
    //this will run based on the condition
    Console.WriteLine("myExpression is falsey but myOtherExpression is truthy");
}
else {
     Console.WriteLine("both myExpression and myOtherExpression are falsey");
}
```

#### For loop

Note: i will leak, also you can use curly brackets like if

```js
for(var i = 0; i < 42; i++)
    Console.WriteLine(i);
```

#### Each loop

```js
enumerable MyItterator()
{
    yield 42;
    yield 100;
    yield 88;
}
each(var item : MyItterator())
{
    Console.WriteLine(item);
}


each(var item : [3,7,12])
{
    Console.WriteLine(item);
}


/*
    This should output
    42
    100
    88
    3
    7
    12
*/
```

#### While loop

```js
while(conditionLikeIf)
{
    Console.WriteLine("Hi");
}

//If conditionLikeIf is falsey we never print Hi
//If conditionLikeIf is truthy we print Hi until it is falsey
```

#### Do loop

```js
do(conditionLikeIf)
{
    Console.WriteLine("Hi");
}

//If conditionLikeIf is falsey we print Hi once
//If conditionLikeIf is truthy we print Hi until it is falsey
```



#### Try statement

NOTE: you can't return undefined (but you can return other types) (It will just return from try and will still execute the body past the try statement) due to the try statement being a closure (you can still break and continue due to special TObjects being returned)

```js
try {
    Console.WriteLine("God is good.");
    throw "my error";
    Console.WriteLine("I am lonely, I am never called.");
} 
catch(ex)
{
     Console.WriteLine($"I got an error {ex}.");
} 
finally {
     Console.WriteLine("For God so loved the world that he gave his only begotten Son, that whoever believes in him should not perish but have eternal life.");  
}


/*
    This should print
    God is good.
    I got an error my error.
    For God so loved the world that he gave his only begotten Son, that whoever believes in him should not perish but have eternal life.
*/
```

#### Switch statement

NOTE: you can use dictionaries with overloaded equals operator (we will pass the switch's expression as the argument)

```js
o = {
    operator== = (this,v) => {
          //this is implicitly passed by runtime, but you must declare it if you want it
          return (v * 7) == 42;
    }
};

var val = 6;

switch(val)
{
    case 4:
        Console.WriteLine("I am four");
        break;
    case 5:
        Console.WriteLine("I am five");
        break;
    case o:
        Console.WriteLine("Hitchhiker's guide to the galaxy meaning of life");
        break;
    default:
        Console.WriteLine("We don't support it we are sorry");
}
```



#### Function declaration

```go
//you can create functions on dictionaries so long as they are on root environment (they are declared there before root scope is evaluated so this is possible)
My.Func.Joel = 59; //Because My.Func.Is.A.Few.Deep creates the dictionaries via runtime

func My.Func.Is.A.Few.Deep(a, b)
{
    return a * b;
}
func main(args)
{
    Console.WriteLine(My.Func.Is.A.Few.Deep(6,7));
}
```

#### Function inside a function

Oh yeah functions can have exclusively a expression as a body which does not need a return keyword

```go
func main(args)
{
    func MyOther(a,b) a * b;
    Console.WriteLine(MyOther(a,b));
}
```

#### Document a function

```go
/^ 
    This function returns 42
^/
func MyFunction() 42;
```

#### Return statement

You can also return nothing

```js
return 42;
return;
```

#### Yield statement

This will halt the function's execution and return the running function object (were you can pop the item and resume it)

To automaticly make a function enumerable (with each statement) you must use ``enumerable`` instead of func when declaring your function

```js
yield 42;
```

#### Throw statement

You can catch this with ``try statement`` with ``catch`` clause

```js
throw "You can replace me with another string or any other object";
```

#### Defer statement

Your code will be called when your scope is destroyed

```go
{
    defer {
        Console.WriteLine("In defer");
    }
    Console.WriteLine("About to leave scope");
}
Console.WriteLine("Left scope");


/*
The output should be

About to leave scope
In defer
Left scope
*/
```

## Expressions

We will place it as a parameter to a function ``doThing`` but these will work anywhere like setting a variable or another expression

#### Undefined

```js
doThing(undefined);
```

#### Null

```js
doThing(null);
```

#### Boolean

```js
doThing(false);
doThing(true);
```

#### Long

A signed 64 bit number

```js
doThing(94);
doThing(599929022);
```

#### Double

A 64 bit floating pointer number

```js
doThing(5.25);
doThing(942.90204);
```

#### Char

Yes we support single character strings (this escapes a double quote)

```csharp
doThing('\"');
```

#### String

Second is an interopolated string

```csharp
doThing("Hi");
doThing($"My name is {name}");
```

#### List

```js
doThing(
    [4,5,9,42,true,"Hi",'\n']
);
```

#### Dictionary

```js
doThing(
    {
        a = "This is an option",
        b = 42,
        c = 9
    }
);
```

###### Enumerating a dictionary

```js
var dict = { a = 5, b = 42};
each(var item : Dictionary.Items(dict))
{
    Console.WriteLine($"Key: {item.Key}");
    Console.WriteLine($"Value: {item.Value}");
    Console.WriteLine();
}
/*
This prints
Key: a
Value: 5

Key: b
Value: 42

*/
```



###### Getting a value from dictionary

```go
func doThing(data)
{
   Console.WriteLine(data.b); //will print 42
}
```

###### Setting a value to dictionary

```go
func doThing(data)
{
    data.a = true; //replace a with a different value
    data.someFieldThatDoesNotExist = 9; //define a new field entirely

}
```

###### Methods

Note that this is optional but if you do have it it must be the first argument, the this argument points to the dictionary

```go
var item = {
      myMethod = (this, a, b) => {
            return a * b;
      }
};

Console.WriteLine(item.myMethod(6,7)); //prints 42
```

Or

```go
var item = {};
func item.myMethod(this, a, b)
{
    return  a * b;
}
Console.WriteLine(item.myMethod(6,7)); //prints 42
```

###### Properties

They are declared like every other method except they are prefixed with ``get`` or ``set``

```go
var item = {
      getProp = (this)=>{
          return 42;  
      },
      setProp = (this,v)=>{
           //do something with v
      }
};

Console.WriteLine(item.Prop); //equivalent to Console.WriteLine(item.getProp());

item.Prop = 100; //equivalent to item.setProp(100); will do nothing in this example

```

###### Operator overloading

```js
var item = {
        operator+ = (this,right) => {
             return 4 + a;
        }
        operator- = (this,right) => {
            return 4 - right; //be careful right may be undefined if the negate operator is used
        }
};

Console.WriteLine(item + 5); //prints 9
```

###### Array operator overloading

```js
var item = {
    GetAt = (index)=>{
        return index * 2; //we multiply index by two and return
    },
    SetAt => (index,value)=>{
        Console.WriteLine($"The index was {index} and value was {value}");
    }
};

Console.WriteLine(item[21]); //prints 42
item["Hi"] = "John"; //prints The index was Hi and value was John
```

#### ByteArray

```js
var bA = new ByteArray(1);
ba[0] = 42;
Console.WriteLine(ba.ToString()); //prints *
```

###### ByteArray from string

```js
var bA = new ByteArray("Hi");
//we can get bytes like this bA[0] which will be 72
//we can get length by bA.Count or bA.Length
```

#### Embedding files (you can't do this easily in C/C++ and C# not as easy as this)

```js
var bA = embed("myFile.png"); //will embed the file res/myFile.png
//it is stored as a RESO in the crvm file and bA is a ByteArray
//note the argument MUST be a constant string
//note you can access a subdirectory of res as well just use dir/file.bin
```

#### Streams



###### From an existing file

```js
var strm = FS.Local.OpenFile("file.bin","rb");

var data = new ByteArray(1024);
var read = strm.Read(data,0,data.Count); 
//use ReadBlock to ensure you have 1024 bytes if not near end of stream

//use WriteBlock to ensure you write the amount you say you need

strm.Close();
```

#### VFS

```js
var myVFS = FS.Local; //FS.Local is the local filesystem


myVFS.CreateDirectory("myDir"); //creates directory in current dir (only local)

myVFS.DeleteDirectory("myDir"); //now we delete it


myVFS.CreateDirectory(Path.FromString(Env.Downloads) / "Folder in Downloads"); //Create a folder in downloads
```



#### Path

```js
var path = / "Path" / "To" / "Directory";
var relativePath = ./"another"/"path";
var combined = path / relativePath;
var someString = "joel";
var combinedAndStr = combined / someString;
var combinedWithExtension = combined + ".mp4";
Console.WriteLine(combined); // outputs /Path/To/Directory/another/path
Console.WriteLine(combined); // outputs /Path/To/Directory/another/path/joel
Console.WriteLine(combinedWithExtension); //outputs /Path/To/Directory/another/path.mp4
//these paths are used with vfs


//to get parent directory use combined.GetParent();
//to get filename use combined.GetFileName();
//to get extension use combinedWithExtension.GetExtension();, it will be the extension including .
//to change the extension use combinedWithExtension.ChangeExtension(".mkv");
//to remove the extension use combinedWithExtension.ChangeExtension(null); or combinedWithExtension.ChangeExtension();
```

#### Html Litterals
```go
//comments are just crosslang ones

//we will be setting to myHtml for the html (returns a string) (it is already html escaped)
myHtml = <h1>{someStringExpression}</h1>;

//a link, in this example we have a dictionary named node with string fields href and text
//lets say node.text equaled List<int> and href contained ./mypage?name=Joel&file=steve.bin myHtml would be equal to "<a target=\"_blank\" href=\"./mypage?name=Joel&amp;file=steve.bin\">List&lt;int&gt;</a>" (the \ are just there to make this a valid string for demonstration purposes, there aren't really backslashes)
myHtml = <a target="_blank" href={node.href}>{node.text}</a>;


//for (works like for loop but is in html form, the for part is not rendered in the final string)
myHtml = <for(var i = 0; i < 42; i++)>
         <h6>{i}</h6> 
       </for>;

//each
myHtml = <each(var item : list)></each>;

//do
myHtml = <do(expr == 42)></do>;

//while
myHtml = <while(expr == 42)></while>;

//if

myHtml = <if(expr == 42)>
    <true>
        //if expr is 42
    </true>
    <false>
        //if expr is not 42
        //you would use another if here instead of else if
    </false>
</if>;

myHtml = <null>Hello</null>; //would just be Hello (useful for templating as it works just like div but the null part is not emited into string)

myHtml = <raw(stringExpr)>; //allowing you to emit unescaped html from string into html litteral (useful for templating)
```