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ewasm “WRC20” token contract coding challenge

This document describes a simple contract in pseudocode and gives a couple of test cases for it.

The challenge is designed to be fairly easy to implement in a language of choice, compiled to wasm and interacted with. It is loosely based on the ERC20 token standard, named "WRC20", where the W stands for WebAssembly.

External interface

The contract has two features:

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.
Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

Render PDF from Markdown that using mermaid

You will need:

Pandoc

This guide is based on Ubuntu, for other OS, use their package manager instead.

prerequisites

Compile the program in gcc with debug symbols enabled (-g)
Do NOT strip the binary
To generate assembly code using gcc use the -S option: gcc -S hello.c

	# This example using
	# Nim: 0.18.0
	# Jester: 0.2.1
	# Using Jester >= 0.3.0 is preferrable if your Nim version > 0.18.0
	# In case you're using Jester >= 0.3.0, look the syntax different
	# in its example because it's not backward compatible

	import db_sqlite, asyncdispatch, json, strformat, strutils, sequtils

	import jester

	/*
	Copyright (C) 2018 Rich Talbot-Watkins

	This file is part of VirtualBeeb.

	VirtualBeeb is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	"""
	nim_magic.py
	Jupyter cell magic for your favorite programming language.

	This is now also available as a proper repo:
	https://github.com/apahl/nim_magic

	All further changes will be tracked there.

	Requirements: Nim (https://nim-lang.org), nimpy (`nimble install nimpy`, thanks to @yglukhov for this great library!)

	import asyncdispatch
	import asynctools
	import docopt
	import json
	import nre
	import os
	import ospaths
	import sequtils
	import sha256/sha256sum
	import strutils

	import macros

	macro lc(init, body): untyped =
	# analyse the body, find the deepest expression 'it' and replace it via
	# 'result.add it'
	let res = genSym(nskVar, "lcResult")

	proc detectForLoopVar(n: NimNode): NimNode =
	if n.kind == nnkForStmt:
	result = n[0]