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Writing Functionally Pure Code

Is all my code going to be pure?

Nope. No program can be composed 100% of pure code because every program must do I/O work, which is inherently stateful. Most programs also need to carry around some amount of internal state, to one degree or another. The goal of functional programming, then, is to maximize the proportion of pure code to impure code in your program.

Pure vs. Impure

What does it mean for data and code to be pure? The short answer is that pure things are immutable, but this is not quite accurate: all pure things are immutable, but not all immutable things are pure. Pure things are not only unmodifiable but also definitional.

Mosh (mobile shell) is a gift from the Gods(tm). Anyone with spotty internet or wireless connection has suffered the pain of a lost SSH session. Sure, one can fire up screen (or tmux as the kids are using these days), but that's an extra step and you are still using the SSH protocol.

I'm not here to tout the benefits of Mosh, you came here to open it up in your firewall.

Create the following file as /etc/firewalld/services/mosh.xml
firewall-cmd --add-service=mosh --permanent
firewall-cmd --reload

If you tend to have a lot of sessions (not recommended), you can increase the ports, but the default should be fine for most applications.

Functional Programming Javascript: using Partials

Partials are basically functions that return functions with some already predefined arguments and need some arguments to be completed. Let's say you have a function with several arguments to be set, but you don't want to set the majority of arguments over and over again because you need it more than once.

# my useless function to write something to the dom
function writeSomethingToDom(element, content){
	element.append(content);
}

# use the function repeatedly

This is not intended to be comprehensive or authoritative, just free online resources I've found valuable while learning more about Erlang.

	# An implementation of the Maybe monad for Nim
	# This implements the traditional operations, bind(called chain)
	# and return(called box) as well as a few useful operators for
	# cleaning up usage of the monad. Also implemented the functor
	# operation fmap(called map) which allows a procedure to be called
	# on a wrapped value

	type
	Maybe*[T] = object
	case valid*: bool

	# check swap usage
	sysctl vm.swapusage

	# disable encrypted swap - SNOW LEOPARD
	sudo defaults write /Library/Preferences/com.apple.virtualMemory UseEncryptedSwap -boolean no

	# disable encrypted swap - LION
	sudo defaults write /Library/Preferences/com.apple.virtualMemory DisableEncryptedSwap -boolean yes

	# disable swap

	;(use '[clojure.tools.macro :only [symbol-macrolet]])

	(defmacro letrec
	"Like let, but the bindings may be mutually recursive, provided that
	the heads of all values can be evaluated independently.

	This means that functions, lazy sequences, delays and the like can
	refer to other bindings regardless of the order in which they
	appear in the letrec form."
	[bindings & body]

	# Makefile for building keil projects
	KEIL=wine "/home/bliker/.wine/drive_c/Keil/UV4/UV4.exe"
	TMP=/tmp/keil.out
	NULL=/dev/null

	# Will prevent it from exiting even when somehing failied
	build:
	-@$(KEIL) -j0 -b -o $(TMP) *.uvproj 2> $(NULL);
	@cat $(TMP)

Crosstyan crosstyan

Writing Functionally Pure Code

Is all my code going to be pure?

Pure vs. Impure

Functional Programming Javascript: using Partials

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	$ redis-cli
	> config set stop-writes-on-bgsave-error no