mys 0.12.0

Strongly typed Python to C++ transpiler.

🐁 Mys

The Mys (/maɪs/) programming language - an attempt to create a statically typed Python-like language that produces fast binaries.

Mys is heavily inspired by Python’s syntax and Rust’s packaging.

Project homepage: https://github.com/eerimoq/mys

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IMPORTANT INFORMATION

Mys is currently this README (the language specification), the examples folder that contains Mys packages, and the tests folder that contains Mys source code (.mys) and it’s manually written “generated” C++ code (.mys.cpp).

The language and build system implementation is hardcoded to build and run the Hello World appliaction, so it’s not yet useful to anyone.

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Installation

$ pip install mys

You must also have a recent versions of g++ and make installed.

Tutorial

First of all, create a package called foo and enter it. This package is used in throughout the tutorial.

$ mys new foo
$ cd foo

Two files are created; Package.toml and src/main.mys. Package.toml contains the package configuration and src/main.mys the application source code.

The source code is the hello world application looks like this:

def main():
    print('Hello, world!')

Build and run the application with mys run. It prints Hello, world!, just as expected.

$ mys run
Hello, world!

Replace the code in src/main.mys with the code below. It examplifies how to use functions, classes, exceptions, types and command line arguments. The syntax is almost identical to Python, so most readers should easily understand it.

def func_1(a: int) -> (int, Final[str]):
    return 2 * a, 'Bar'


def func_2(a: int, b: int=1) -> int:
    for i in range(b):
        a += i * b

    return a


def func_3(a: Optional[int]) -> int:
    if a is None:
        return 0
    else:
        return 2 * a


def func_4(a: int) -> {int: [float]}:
    return {
        1: [],
        10 * a: [7.5, -1.0]
    }


def func_5():
    try:
        raise Exception()
    except:
        print('func_5():      An exception occurred.')


class Calc:

    def __init__(self, value: int):
        self.value = value

    def triple(self):
        self.value *= 3


def main(args: [str]):
    value = int(args[1])
    print('func_1(value):', func_1(value))
    print('func_2(value):', func_2(value))
    print('func_3(None): ', func_3(None))
    print('func_3(value):', func_3(value))
    print('func_4(value):', func_4(value))
    func_5()
    calc = Calc(value)
    calc.triple()
    print('calc:         ', calc)

Build and run it.

$ mys run 5
func_1(value): (5, 'Bar')
func_2(value): 7
func_3(None):  0
func_3(value): 10
func_4(value): {1: [], 50: [7.5, -1,0]}
func_5():      An exception occurred.
calc:          Calc(value=15)

Built-in functions and classes

Built-in functions and classes
abs()	all()	any()	bool()	bytes()
chr()	dict()	divmod()	enumerate()	f32()
f64()	float()	format()	int()	len()
list()	min()	max()	open()	ord()
print()	range()	reversed()	round()	s8()
s16()	s32()	s64()	str()	sum()
tuple()	u8()	u16()	u32()	u64()
zip()

All built-ins aims to behave like their Python counterparts, with the following differences.

• abs() only supports integer and floating point numbers.

• all() and any() only supports lists of bool().

• u8(), u16(), u32(), u64(), s8(), s16(), s32() and s64() behaves like int().

• f32() and f64() behaves like float().

• min() and max() only supports lists of integer and floating point numbers, and a fixed number of integer and floating points parameters.

• sum() only supports lists of integer and floating point numbers.

Types

Variables may all be set to None if declared as Optional.

Variables declared as Final can’t be modified.

Type	Example	Comment
int	1, -1000	An integer. Usually 32 or 64 bits.
u8, u16, u32, u64	5, 200	An 8/16/32/64 bits unsigned integer.
s8, s16, s32, s64	-33, 100	An 8/16/32/64 bits signed integer.
float	5.5, -100.0	A floating point number. Usually 32 bits.
f32, f64	5.3, -100.0	A 32/64 bits floating point number.
str	'Hi!'	A unicode string.
bytes	b'\x00\x43'	A sequence of bytes.
tuple(T1, T2, ...)	(5.0, 5, 'foo')	A tuple with items of types T1, T2, etc.
list(T)	[5, 10, 1]	A list with items of type T.
dict(TK, TV)	{5: 'a', -1: 'b'}	A dictionary with keys of type TK and values of type TV.

Memory management

Integers and floating point numbers are allocated on the stack, passed by value to functions and returned by value from functions, just as any C++ program.

Strings, bytes, tuples, lists, dicts and classes are normally allocated on the heap and managed by C++ shared pointers. Objects that are known not to outlive a function are allocated on the stack.

There is no garbage collector, as there is no garbage to collect. Reference counting is used instead.

Major differences to Python

• All variables must have a known type at compile time. The same applies to function parameters and return value.

• Threads can run in parallel. No GIL exists.

  WARNING: Data races will occur when multiple threads uses a variable at the same time, which will likely make the program crash.

• Integers and floats have a platform dependent maximum size, usually 32 or 64 bits.

• Decorators does not exist.

• Variable function arguments *args and **kwargs are not supported, except to some built-in functions.

• Async is not supported.

• Generators are not supported.

• The majority of the standard library is not implemented.

• Dictionary keys must be integers, floats, strings or bytes.

• Strings, bytes and tuple items are mutable by default. Mark them as Final to make them immutable.

• Classes and functions are private by default. Decorate them with @public to make them public. Variables are always private.

Text editor settings

Visual Code

Use the Python language for *.mys files by modifying your files.associations setting.

See the official Visual Code guide for more detils.

"files.associations": {
    "*.mys": "python"
}

Emacs

Use the Python mode for *.mys files by adding the following to your .emacs configuration file.

(add-to-list 'auto-mode-alist '("\\.mys\\'" . python-mode))

Performance

ToDo: Create a benchmark and present its outcome in this section.

Build time

Mys should be slower.

Startup time

Mys should be faster.

Runtime

Mys should be faster.

Memory usage

Mys should use less memory.

Build process

mys run and mys build does the following:

1. Uses Python’s parser to transform the source code to an Abstract Syntax Tree (AST).

2. Generates C++ code from the AST.

3. Compiles the C++ code with g++.

4. Statically links the program with g++.