Eason Huang Eason0210

Notes and Exercises from Chapter 5 of Haskell Book

Benefits of a type system:

Many errors caught before program execution, at compile time
Compiler optimizations
Documentation of programs
Less code to write because you don't have to validate data at every step

Many, perhaps most, programming languages have type systems that feel like haggling with a petty merchant. Haskell provides a type system that more closely resembles a quiet, pleasant conversation with a colleague than an argument in the bazaar.

Install MSYS2

Manual is on the home page http://www.msys2.org/

Run MINGW32 (32 bit environment) and update it

pacman --needed -Syu

Install dependencies

Automatic python version plus venv

Goal

For easy editor integration and command-line usage, we'd like to be able to specify a Python version per project, with its own virtualenv to isolate its libraries from those of other projects.

We're willing to change $PATH globally once, but not per project. And we'd like to avoid having to run every python command invocation in a special subshell created by a shell wrapper. Instead, simply invoking "python" or "pip" etc. should do the right thing, based on the directory in which it is invoked.

It turns out this is possible!

Nix on macOS Catalina

I'm writing this gist for my own records but it might help someone else too.

Installing Nix

Support for Catalina has improved a lot since the update was first rolled out.

Note: See the NixOS manual for discussion of the --darwin-use-unencrypted-nix-store-volume option.

Debug with GDB on macOS 11

The big reason to do this is that LLDB has no ability to "follow-fork-mode child", in other words, a multi-process target that doesn't have a single-process mode (or, a bug that only manifests when in multi-process mode) is going to be difficult or impossible to debug, especially if you have to run the target over and over in order to make the bug manifest. If you have a repeatable bug, no big deal, break on the fork from the parent process and attach to the child in a second lldb instance. Otherwise, read on.

Install GDB

Don't make the mistake of thinking you can just brew install gdb. Currently this is version 10.2 and it's mostly broken, with at least two annoying bugs as of April 29th 2021, but the big one is https://sourceware.org/bugzilla/show_bug.cgi?id=24069

$ xcode-select install  # install the XCode command-line tools

	阿爸 a1'ba4 18137
	阿昌族 a1'chang1'zu2 50849
	阿斗 a1'dou3 42632
	阿飞 a1'fei1 48603
	阿富汗 a1'fu4'han4 3461
	阿訇 a1'hong1 34432
	阿拉伯数字 a1'la1'bo2'shu4'zi4 35937
	阿拉伯语 a1'la1'bo2'yu3 30476
	阿妈 a1'ma1 16220
	阿门 a1'men2 47913

	let
	fontOverlay = import ./font-overlays.nix;
	pkgsOverlay = import ./pkgs-overlay.nix;
	user = "anhduy";
	in

	{ config, pkgs, ... }:

	{
	imports = [ <home-manager/nix-darwin> ];

	# Instructions for fresh install

	$ sh <(curl -L https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume --daemon
	# reboot
	$ source /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh
	$ echo 'export NIX_PATH=darwin-config=$HOME/.nixpkgs/darwin-configuration.nix:$HOME/.nix-defexpr/channels${NIX_PATH:+:}$NIX_PATH' \| tee -a ~/.zshrc
	$ echo 'source $HOME/.nix-profile/etc/profile.d/hm-session-vars.sh' \| tee -a ~/.zshrc
	$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
	$ nix-channel --add https://github.com/LnL7/nix-darwin/archive/master.tar.gz darwin
	$ nix-channel --add https://github.com/nix-community/home-manager/archive/master.tar.gz home-manager