Seven Languages in Seven Weeks: Io, Day 2

Today is Day 2 of Io in my Seven Languages in Seven Weeks series of blog posts. You can check out Day 1 of IO here.

Io, Day 2: Thoughts

Day 2 made some huge leaps and bounds over the basic syntax introduced in Day 1. The key learning from this day is that in Io, just about everything is a message sent to an object. There aren't separate semantics for calling functions, using control structures, or defining objects: those are all just objects reacting to some sort of message.

One of the most startling examples of this is the realization that even the basic operators in Io, such as +, -, and *, are actually messages. That is, the code "2 + 5" is actually understood as the message "+" being sent to the object 2 with 5 as a parameter. In other words, it could be re-written as "2 +(5)". The "+", then, is just a method defined on the number object that takes another number as a parameter.

This makes supporting operators on custom objects simple: all I have to do is define a "slot" with the operator's name. For example, here's an object for complex numbers that can be used with the "+" operator:

	Complex := Object clone do (
	setValues := method(real, imaginary,
	self real := real;
	self imaginary := imaginary;
	self
	)
	+ := method(other,
	result := Complex clone setValues(self real + other real, self imaginary + other imaginary)
	)
	)
	c1 := Complex clone setValues(1, 2)
	c2 := Complex clone setValues(3, 4)
	c3 := c1 + c2
	c3 println
	/*
	Complex_0x22ee90:
	imaginary = 6
	real = 4
	*/

view raw ComplexNumbers.io hosted with ❤ by GitHub

I found this fairly eye opening. As I think of the syntaxes of other languages I'm used to, such as Java, there are "special cases" all over the place. For example, the "+" operator has special code to handle addition for numbers and String concatenation and nothing else; for loops, while loops, if statements, defining classes, and so on are all special syntax features. In Io, they are all just objects responding to messages.

Io, Day 2: Problems

Fibonacci

Write a program to find the nth Fibonacci number. Both the recursive and iterative solutions are included:

	fib_recursive := method(n,
	if(n < 3, 1, fib_recursive(n - 1) + fib_recursive(n - 2))
	)
	fib_iterative := method(n,
	prev_prev := 0
	prev := 0
	sum := 1
	for(i, 2, n,
	prev_prev = prev
	prev = sum
	sum = prev + prev_prev
	)
	sum
	)
	"-- Recursive Fibonacci --" println
	for(i, 1, 10, fib_recursive(i) println)
	"" println
	"-- Iterative Fibonacci --" println
	for(i, 1, 10, fib_iterative(i) println)
	/*
	-- Recursive Fibonacci --
	1
	1
	2
	3
	5
	8
	13
	21
	34
	55
	-- Iterative Fibonacci --
	1
	1
	2
	3
	5
	8
	13
	21
	34
	55
	*/

view raw Fibonacci.io hosted with ❤ by GitHub

Safe division

How would you change the "/" operator to return 0 if the denominator is zero?

	(1 / 0) println // inf
	(1 / 2) println // 0.5
	Number originalDivision := Number getSlot("/")
	Number / := method(other,
	if (other == 0, 0, self originalDivision(other))
	)
	(1 / 0) println // 0
	(1 / 2) println // 0.5

view raw SafeDivision.io hosted with ❤ by GitHub

2d add

Write a program to add up all the values in a 2-dimensional array.

	sum2dArray := method(arr,
	arr flatten sum
	)
	arr := list(list(1, 2), list(3, 4), 5, list(6, 7, 8), 9, 10)
	sum2dArray(arr) println // 55

view raw Sum2dArray.io hosted with ❤ by GitHub

myAverage

Add a slot called "myAverage" to a list that computes the average of all the numbers in a list. Bonus: raise an exception if any item in the list is not a number.

	List myAverage := method(
	sum := 0
	self foreach(i, v, if(v type == "Number", sum = sum + v, Exception raise("#{v} is not a Number" interpolate)))
	sum / (self size)
	)
	list(1) myAverage println // 1
	list(3, 3, 3) myAverage println // 3
	list(1, 2, 3, 4, 5, 6, 7, 8, 9) myAverage println // 5
	list(1, "A", 3) myAverage println // Exception: A is not a Number

view raw myAverage.io hosted with ❤ by GitHub

Two Dimensional List

Write a prototype for a two-dimensional list. The dim(x, y) method should allocate a list of y lists that are x elements long. set(x, y, value) should set a value and get(x, y) should return that value. Write a transpose method so that new_matrix get(y, x) == original_matrix get(x, y). Write the matrix to a file and read the matrix from a file.

	TwoDList := Object clone do (
	init := method(
	self lists := list()
	)
	dim := method(x, y,
	self lists preallocateToSize(y)
	for(i, 0, y - 1, self lists append(list() preallocateToSize(x)))
	self
	)
	set := method(x, y, value,
	self lists at(y) atInsert(x, value)
	)
	get := method(x, y,
	self lists at(y) at(x)
	)
	transpose := method(
	transposedList := TwoDList clone dim(self lists size, self lists at(0) size)
	self lists foreach(y, subList,
	subList foreach(x, value,
	transposedList set(y, x, value)
	)
	)
	transposedList
	)
	println := method(
	self lists foreach(y, subList,
	subList foreach(x, value,
	if(x == 0 or x == subList size, "|" print)
	" #{get(x, y)} |" interpolate print
	)
	"" println
	)
	)
	toFile := method(name,
	File with(name) open write(self serialized) close
	)
	fromFile := method(name,
	doRelativeFile(name)
	)
	)
	list = TwoDList clone dim(2, 3)
	list set(0, 0, "A")
	list set(1, 0, "B")
	list set(0, 1, "C")
	list set(1, 1, "D")
	list set(0, 2, "E")
	list set(1, 2, "F")
	transposedList := list transpose
	transposedList toFile("transposed.txt")
	transposedListFromFile := TwoDList fromFile("transposed.txt")
	"2x3 list:" println
	list println
	"Transposed 3x2 list:" println
	transposedList println
	"Transposed 3x2 list from file:" println
	transposedListFromFile println
	/*
	2x3 list:
	| A | B |
	| C | D |
	| E | F |
	Transposed 3x2 list:
	| A | C | E |
	| B | D | F |
	Transposed 3x2 list from file:
	| A | C | E |
	| B | D | F |
	*/

view raw TwoDimensionalArray.io hosted with ❤ by GitHub

Guess Number

Write a program that gives you ten tries to guess a random number from 1-100. Give a hint of "hotter" or "colder" for each guess after the first one.

	// Can't use Random due to http://stackoverflow.com/questions/3481651/how-do-i-import-an-addon-in-the-io-language
	// toGuess := Random value(100) ceil
	// A random number as per http://xkcd.com/221/
	toGuess := 4
	guessCounter := 0
	previousDiff := nil
	currentDiff := nil
	while(guessCounter < 10,
	guessCounter = guessCounter + 1
	currentGuess := File standardInput readLine("Enter your guess: ") asNumber()
	currentDiff := (toGuess - currentGuess) abs
	if(currentDiff == 0) then (
	guessCounter = 10
	) else (
	if (previousDiff == nil) then("Try again" println) elseif(currentDiff == previousDiff) then ("You just guessed that!" println) elseif(currentDiff < previousDiff) then ("Hotter" println) else("Colder" println)
	previousDiff = currentDiff
	)
	)
	if(currentDiff == 0, "Correct!", "Sorry, you ran out of guesses.") println

view raw GuessNumber.io hosted with ❤ by GitHub

On to day 3!

Continue on to day 3 of Io here.