Ekrem Dinçel EkremDincel

Method for Emulating Higher-Kinded Types in Rust

Intro

I've been fiddling about with an idea lately, looking at how higher-kinded types can be represented in such a way that we can reason with them in Rust here and now, without having to wait a couple years for what would be a significant change to the language and compiler.

There have been multiple discussions on introducing higher-ranked polymorphism into Rust, using Haskell-style Higher-Kinded Types (HKTs) or Scala-looking Generalised Associated Types (GATs). The benefit of higher-ranked polymorphism is to allow higher-level, richer abstractions and pattern expression than just the rank-1 polymorphism we have today.

As an example, currently we can express this type:

	from contextlib import contextmanager
	from timeit import default_timer as timer
	try:
	import matplotlib
	except ModuleNotFoundError:
	PLOT = False
	else:
	PLOT = True

	class Profiler:

	def windows(sequence, step):
	i = 0
	while i < len(sequence):
	yield sequence[i: i + step]
	i += step

	def filled_windows(sequence, step):
	i = 0
	while i + step <= len(sequence):
	yield sequence[i: i + step]

	#![feature(allocator_api)]
	use core::alloc::Layout;
	use std::alloc::Allocator;
	use std::alloc::Global;

	fn new_array<T, const N: usize>(mut initializer: impl FnMut() -> T) -> Box<[T; N]> {
	// allocate the array with default allocator by using low level API
	let ptr: *mut T = Global
	.allocate(Layout::new::<[T; N]>())
	// panic on Out of Memory

	class EnumMetaDict(dict):

	def __init__(self):
	self.n = -1

	def __getitem__(self, item):
	if item.isupper():
	self.n += 1
	self[item] = self.n
	return self.n

	from functools import reduce, partial
	import itertools as it
	from operator import itemgetter, methodcaller

	def reversed_partial(f, args, *kwargs):
	def wrapper(_args, *_kwargs):
	f(_args, args, _kwargs, kwargs)
	return wrapper

	def unpack(iterable):

	digit = ['sıfır', 'bir', 'iki', 'üç', 'dört', 'beş', 'altı', 'yedi', 'sekiz', 'dokuz']
	digit2 = ['', 'on', 'yirmi', 'otuz', 'kırk', 'elli', 'altmış', 'yetmiş', 'seksen', 'doksan']
	digit3 = ['milyon', 'milyar', 'trilyon', 'katrilyon', 'kentilyon', 'sekstilyon', 'septilyon', 'oktilyon', 'nonilyon', 'desilyon', 'andesilyon', 'dodesilyon', 'tredesilyon', 'katordesilyon', 'kendesilyon', 'seksdesilyon', 'septendesilyon', 'oktodesilyon', 'novemdesilyon', 'vicintilyon', 'anvicintilyon', 'dovicintilyon', 'trevicintilyon', 'katorvicintilyon', 'kenkavicintilyon', 'sesvicintilyon', 'septemvicintilyon', 'oktovicintilyon', 'novemvicintilyon', 'tricintilyon', 'antricintilyon']


	onluk = lambda i: (digit[i] if i<10 else digit2[i // 10] + " " + digit[i % 10]) if i%10 else digit2[i // 10]
	yüzlük = lambda i: onluk(i) if i < 100 else ("yüz " + onluk(i - 100) if i-100 else "yüz") if i < 200 else digit[i // 100] + " yüz " + onluk(i % 100) if i%100 else digit[i // 100] + " yüz"
	binlik = lambda i: ("bin" if i == 1 else yüzlük(i) + "

	import json
	import socket
	from struct import Struct, calcsize
	from select import select

	__all__ = ("Server", "Client", "localhostname", "localhost", "LAN", "WAN")

	_int = "H" # 0 <= number <= 65535 == 2 ** 16 -1
	_size = calcsize(_int)
	_struct = Struct("!" + _int)

	import ast

	with open("module.py", "r") as f: # we will analysis this file
	data = f.read()

	tree = ast.parse(data)

	classes = {} # {class: [parents]}

	for i in tree.body:

	class MyEnum():
	(ONE,
	TWO,
	THREE,
	FOUR,
	FIVE) = range(5)