Dinesh Narayanan ndchandar

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Yoneda Intuition from Humble Beginnings

Let's explore the Yoneda lemma. You don't need to be an advanced Haskeller to understand this. In fact I claim you will understand the first section fine if you're comfortable with map/fmap and id.

I am not out to motivate it, but we will explore Yoneda at the level of terms and at the level of types.

Openssl commands:

openssl genrsa -out self-ssl.key
openssl req -new -key self-ssl.key -out self-ssl.csr -config csr.conf
openssl x509 -req -days 365 -in self-ssl.csr -signkey self-ssl.key -out self-ssl.crt -extensions req_ext -extfile csr.conf

Sign from Root CA: openssl x509 -req -days 365 -extensions req_ext -extfile csr.conf -CA RootCA.crt -CAkey RootCA.key -in self-ssl.csr -out self-ssl.crt

Achieving warp speed with Rust

Applied Functional Programming with Scala - Notes

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

Symbol	Explanation	Hint
`\/`	Right-leaning Either	Split ways, go one way or the other
`-\/`	Left value of `\/`	- is on the left side
`\/-`	Right value of `\/`	- is on the right side
`>>=`	`flatMap`	shove result into
`>>`	`flatMap(_ => ..)`	shove into, but ignore the result
`\|@\|`	Applicatives into Tuple	Scream operator
`\|+\|`	Append via Monoid	+ was taken
`>	`	`fa.map(_ => b)`

This blog post series has moved here.

You might also be interested in the 2016 version.

This is material to go along with a 2014 Boston Haskell talk.

We are going to look at a series of type signatures in Haskell and explore how parametricity (or lack thereof) lets us constrain what a function is allowed to do.

Let's start with a decidedly non-generic function signature. What are the possible implementations of this function which typecheck?

wrangle :: Int -> Int

	/*
	scalaVersion := "2.12.7"

	resolvers += Resolver.sonatypeRepo("snapshots")

	libraryDependencies += "co.fs2" %% "fs2-core" % "1.0.1-SNAPSHOT"
	*/
	import cats._
	import cats.implicits._
	import cats.effect._

	import akka.stream._
	import akka.stream.scaladsl._
	/***
	* Example based on numBuckets = 3
	* --- bucket 1 flow --- ~mapAsync(parallelism)~ ---
	* \|------------------\| / \\|---------------\|
	* Open inlet[A] --- \| Partition Fan Out\| --- bucket 2 flow --- ~mapAsync(parallelism)~ -----\| Merge Fan In \| --- Open outlet[B]
	* \|------------------\| \ /\|---------------\|
	* --- bucket 3 flow --- ~mapAsync(parallelism)~ ---
	*

	import java.io.PrintWriter

	import cascading.stats.CascadingStats
	import com.twitter.scalding._

	/**
	* Writes all custom counters into a tsv file args("counters-file") if this property is set.
	*
	* Output format:
	* counter_name value