Jordan Mackie jmackie

NOTE: a more up-to-date version of this can be found on my blog

nix-shell and Shebang Lines

A few days ago, version 1.9 of the Nix package manager was released. From the release notes:

nix-shell can now be used as a #!-interpreter. This allows you to write scripts that dynamically fetch their own dependencies.

This is the process of setting up erlang, rebar3, and cowboy for a Hello World, starting with a clean Debian 8 install.

Update apt and install deps:

root@046edcaea45a:~# apt-get update
root@046edcaea45a:~# apt-get install erlang erlang-dev gcc
root@046edcaea45a:~# wget https://s3.amazonaws.com/rebar3/rebar3
root@046edcaea45a:~# mkdir ~/bin/
root@046edcaea45a:~# mv rebar3 ~/bin/
root@046edcaea45a:~# chmod +x ~/bin/rebar3

Statically checked overloaded strings

This gist demonstrates a trick I came up with which is defining IsString for Q (TExp a), where a is lift-able. This allows you to write $$("...") and have the string parsed at compile-time.

On GHC 9, you are able to write $$"..." instead.

This offers a light-weight way to enforce compile-time constraints. It's basically OverloadedStrings with static checks. The inferred return type

Github "Verified" commits using GPG key with private email

It's nice to see a Verified message next to each commit for peace of mind.

Using GPG or S/MIME, you can sign tags and commits locally. These tags or commits are marked as verified on GitHub so other people can be confident that the changes come from a trusted source.

Install latest gpg

If using a mac use homebrew

	name=coursecal-d7
	port=$(shell docker inspect -format='{{(index (index .NetworkSettings.Ports "22/tcp") 0).HostPort}}' $(name))


	# launches a debug shell into the latest intermediate docker image
	debug_latest:
	docker run -t -i `docker images -q \| head -n 1` /bin/bash

	# DESTROYS all containers (!!) and all images without a tag
	# NB:

	#! python3.4
	from setuptools import setup
	import os
	import py2exe
	import matplotlib

	includes = ["sip",
	"PyQt5",
	"PyQt5.QtCore",
	"PyQt5.QtGui",

	--Roughly based on https://github.com/Gabriel439/Haskell-Morte-Library/blob/master/src/Morte/Core.hs by Gabriel Gonzalez et al.

	data Expr = Star \| Box \| Var Int \| Lam Int Expr Expr \| Pi Int Expr Expr \| App Expr Expr deriving (Show, Eq)

	subst v e (Var v') \| v == v' = e
	subst v e (Lam v' ta b ) \| v == v' = Lam v' (subst v e ta) b
	subst v e (Lam v' ta b ) = Lam v' (subst v e ta) (subst v e b )
	subst v e (Pi v' ta tb) \| v == v' = Pi v' (subst v e ta) tb
	subst v e (Pi v' ta tb) = Pi v' (subst v e ta) (subst v e tb)
	subst v e (App f a ) = App (subst v e f ) (subst v e a )

	with import <nixpkgs> {};

	let
	jdk = openjdk;
	node = nodejs-10_x;
	sdk = androidenv.androidsdk {
	platformVersions = [ "23" ];
	abiVersions = [ "x86" ];
	useGoogleAPIs = true;
	useExtraSupportLibs = false;

	{-# LANGUAGE BlockArguments #-}
	{-# LANGUAGE DeriveFunctor #-}
	{-# LANGUAGE DeriveGeneric #-}
	{-# LANGUAGE FlexibleContexts #-}
	{-# LANGUAGE MonoLocalBinds #-}
	{-# LANGUAGE RecordWildCards #-}
	{-# LANGUAGE TypeApplications #-}
	module Main where

	import Control.Applicative (Alternative (..))

	// Reference: http://stackoverflow.com/questions/4822471/count-number-of-lines-in-a-git-repository

	$ git ls-files \| xargs wc -l