The jakt programming language

jakt is a memory-safe systems programming language.

It currently transpiles to C++.

NOTE: The language is under heavy development.

Usage

jakt file.jakt
clang++ -std=c++20 -Iruntime -Wno-user-defined-literals output.cpp

Goals

Memory safety
Code readability
Developer productivity
Executable performance
Fun!

Memory safety

The following strategies are employed to achieve memory safety:

Automatic reference counting
Strong typing
Bounds checking
No raw pointers in safe mode

In jakt, there are three pointer types:

T (Strong pointer to reference-counted class T.)
weak T? (Weak pointer to reference-counted class T. Becomes empty on pointee destruction.)
raw T (Raw pointer to arbitrary type T. Only usable in unsafe blocks.)

Null pointers are not possible in safe mode, but pointers can be wrapped in Optional, i.e Optional<T> or T? for short.

Note that weak pointers must always be wrapped in Optional. There is no weak T, only weak T?.

Math safety

Integer overflow (both signed and unsigned) is a runtime error.
Numeric values are not automatically coerced to int. All casts must be explicit.

For cases where silent integer overflow is desired, there are explicit functions that provide this functionality.

Code readability

Far more time is spent reading code than writing it. For that reason, jakt puts a high emphasis on readability.

Some of the features that encourage more readable programs:

Function calls

When calling a function, you must specify the name of each argument as you're passing it:

rect.set_size(width: 640, height: 480)

There are two exceptions to this:

If the parameter in the function declaration is declared as anonymous, omitting the argument label is allowed.
When passing a variable with the same name as the parameter.

Structures and classes

There are two main ways to declare a structure in Jakt: struct and class.

`struct`

Basic syntax:

struct Point {
    x: i64
    y: i64
}

Structs in Jakt have value semantics:

Variables that contain a struct always have a unique instance of the struct.
Copying a struct instance always makes a deep copy.

let a = Point(x: 10, y: 5)
let b = a
// "b" is a deep copy of "a", they do not refer to the same Point

jakt generates a default constructor for structs. It takes all fields by name. For the Point struct above, it looks like this:

Point(x: i64, y: i64)

Struct members are public by default.

`class`

Same basic syntax as struct:

class Size {
    width: i64
    height: i64

    public function area(this) => width * height
}

Classes in Jakt have reference semantics:

Copying a class instance (aka an "object") copies a reference to the object.
All objects are reference-counted by default. This ensures that objects don't get accessed after being deleted.

Class members are private by default.

Member functions

Both structs and classes can have member functions.

There are three kinds of member functions:

Static member functions don't require an object to call. They have no this parameter.

class Foo {
    function func() => println("Hello!")
}

// Foo::func() can be called without an object.
Foo::func()

Non-mutating member functions require an object to be called, but cannot mutate the object. The first parameter is this.

class Foo {
    function func(this) => println("Hello!")
}

// Foo::func() can only be called on an instance of Foo.
let x = Foo()
x.func()

Mutating member functions require an object to be called, and may modify the object. The first parameter is mutable this.

class Foo {
    x: i64

    function set(mutable this, anonymous x: i64) {
        this.x = x
    }
}

// Foo::set() can only be called on a mutable Foo:
let mutable foo = Foo(x: 3)
foo.set(9)

Arrays

Dynamic arrays are provided via a built-in Array<T> type. They can grow and shrink at runtime.

Array is memory safe:

Out-of-bounds will panic the program with a runtime error.
Slices of an Array keep the underlying data alive via automatic reference counting.

Declaring arrays

// Function that takes an Array<i64> and returns an Array<String>
function foo(numbers: [i64]) -> [String] {
    ...
}

Shorthand for creating arrays

// Array<i64> with 256 elements, all initialized to 0.
let values = [0; 256]

// Array<String> with 3 elements: "foo", "bar" and "baz".
let values = ["foo", "bar", "baz"]

Dictionaries

Creating dictionaries
Indexing dictionaries
Assigning into indexes (aka lvalue)

function main() {
    let dict = ["a": 1, "b": 2]

    println("{}", dict["a"]!)
}

Tuples

Creating tuples
Index tuples
Tuple types

function main() {
    let x = ("a", 2, true)

    println("{}", x.1)
}

Enums and Pattern Matching

Enums as sum-types
Generic enums
Enums as names for values of an underlying type (partial)
match expressions
Enum scope inference in match arms
Nested match patterns
Traits as match patterns
Support for interop with the ?, ?? and ! operators

enum MyOptional<T> {
    Some: T
    None
}

function value_or_default<T>(anonymous x: MyOptional<T>, default: T) -> T {
    return match x {
        Some(value) => value
        None => default
    }
}

// Not yet implemented:
enum Foo {
    StructLikeThingy {
        field_a: i32
        field_b: i32
    }
}

function look_at_foo(anonymous x: Foo) -> i32 {
    match x {
        StructureLikeThingy(field_a: a, field_b: b) => {
            return a + b
        }
    }
}

Generics

Generic types
Generic type inference
Traits

Jakt supports both generic structures and generic functions.

function id<T>(anonymous x: T) -> T {
    return x
}

function main() {
    let y = id(3)

    println("{}", y + 1000)
}

struct Foo<T> {
    x: T
}

function main() {
    let f = Foo(x: 100)

    println("{}", f.x)
}

Type casts

There are four built-in casting operators in jakt.

Casts for all types

as? T: Returns an Optional<T>, empty if the source value isn't convertible to T.
as! T: Returns a T, aborts the program if the source value isn't convertible to T.

Casts specific to numeric types

as truncated T: Returns a T with out-of-range values truncated in a manner specific to each type.
as saturated T: Returns a T with the out-of-range values saturated to the minimum or maximum value possible for T.

Namespaces

(Not yet implemented)

namespace Foo {
    function bar() => 3
}

function main() {
    println("{}", Foo::bar())
}

Traits

(Not yet implemented)

To make generics a bit more powerful and expressive, you can add additional information to them:

trait Hashable {
    function hash(self) -> i128
}

class Foo implements Hashable {
    function hash(self) => 42
}

type i64 implements Hashable {
    function hash(self) => 100
}

The intention is that generics use traits to limit what is passed into a generic parameter, and also to grant that variable more capabilities in the body. It's not really intended to do vtable types of things (for that, just use a subclass)

Safety analysis

(Not yet implemented)

To keep things safe, there are a few kinds of analysis we'd like to do (non-exhaustive):

Preventing overlapping of method calls that would collide with each other. For example, creating an iterator over a container, and while that's live, resizing the container
Using and manipulating raw pointers
Calling out to C code that may have side effects

Error handling

Functions that can fail with an error instead of returning normally are marked with the throws keyword:

function task_that_might_fail() throws -> usize {
    if problem {
        throw Error::from_errno(EPROBLEM)
    }
    ...
    return result
}

function task_that_cannot_fail() -> usize {
    ...
    return result
}

Unlike languages like C++ and Java, errors don't unwind the call stack automatically. Instead, they bubble up to the nearest caller.

If nothing else is specified, calling a function that throws from within a function that throws will implicitly bubble errors.

Syntax for catching errors

If you want to catch errors locally instead of letting them bubble up to the caller, use a try/catch construct like this:

try {
    task_that_might_fail()
} catch error {
    println("Caught error: {}", error)
}

There's also a shorter form:

try task_that_might_fail() catch error {
    println("Caught error: {}", error)
}

Rethrowing errors

(Not yet implemented)

Inline C++

For better interoperability with existing C++ code, as well as situations where the capabilities of jakt within unsafe blocks are not powerful enough, the possibility of embedding inline C++ code into the program exists in the form of cpp blocks:

let mutable x = 0
unsafe {
    cpp {
        "x = (i64)&x;"
    }
}
println("{}", x)

reaganmcf / jakt

The jakt programming language

Usage

Goals

Memory safety

Math safety

Code readability

Function calls

Structures and classes

`struct`

`class`

Member functions

Arrays

Declaring arrays

Shorthand for creating arrays

Dictionaries

Tuples

Enums and Pattern Matching

Generics

Type casts

Casts for all types

Casts specific to numeric types

Namespaces

Traits

Safety analysis

Error handling

Syntax for catching errors

Rethrowing errors

Inline C++

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