calebsander

CC = clang-with-asan
CFLAGS = -Wall -Wextra

graph: function.o graph.o main.o
	$(CC) $(CFLAGS) -lm $^ -o $@

%.o: %.c
	$(CC) $(CFLAGS) -c $^ -o $@

calebsander

An introduction to monads (in Haskell)

Motivation

Consider how stateful computations could be expressed in a pure functional language like Haskell. We will use a mutable stack as an example, but we'll see later that the same ideas generalize to any sort of mutable state.

A stack is a simple data structure used extensively to model imperative computation. It is an ordered collection of values where all modifications happen at one end of the collection. In Java, for example, a Stack is accessed/manipulated with the following two methods:

calebsander

(module
	;; Memory layout
	;; 0 - 63: lookup
	;; 64 - 186: revLookup
	;; 187 - : input, followed by output
	(global $INPUT (export "INPUT") i32 (i32.const 187))
	(memory (export "memory") 1)
	(data (i32.const 0) "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
	(func (export "init")
		(local $i i32)

calebsander

Arrays

• Create a new array with n elements, each initialized to x

new Array(n).fill(x)

• Create a new array with n elements, each initialized as f()

// Imperatively
const a = []
for (let i = 0; i < n; i++) a[i] = f()

calebsander

#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
  #include <avr/power.h>
#endif

#define START_PIN 3
#define NUM_STRIPS 3
#define NUM_PIXELS 150

// Parameter 1 = number of pixels in strip

calebsander

function Fraction(n, d) {
  this.n = n;
  if (d) this.d = d;
  else this.d = 1;
}

Fraction.prototype.reciprocal = function() {
  return {n: this.d, d: this.n};
}