The latest instance of the course can be found at: O1: 2024
Luet oppimateriaalin englanninkielistä versiota. Mainitsit kuitenkin taustakyselyssä osaavasi suomea. Siksi suosittelemme, että käytät suomenkielistä versiota, joka on testatumpi ja hieman laajempi ja muutenkin mukava.
Suomenkielinen materiaali kyllä esittelee englanninkielisetkin termit.
Kieli vaihtuu A+:n sivujen yläreunan painikkeesta. Tai tästä: Vaihda suomeksi.
Chapter 6.3: Collections and Snakes
About This Page
Questions Answered: How do higher-order methods make collections easy and pleasant to work with?
Topics: Methods on collections. We’ll also continue to use function literals a lot.
What Will I Do? Read and program.
Rough Estimate of Workload:? Three or four hours.
Points Available: A35 + B100.
Introduction
This chapter will introduce you to a diverse set of higher-order methods that you can use instead of loops, or in combination with them. All of these methods have a couple of things in common: they are provided by the collection classes of the Scala API and they take in functions that specify what to do with the elements of the target collection. The methods respond to needs such as these:
How can I repeat an operation on each element of a collection?
How can I examine a collection’s overall properties (e.g., whether all of its elements are similar to each other in some respect)?
How can I select some of a collection’s elements (e.g., all the elements that match a particular criterion)?
How can I combine elements to produce a result (e.g., the sum of squares of all elements, or a combination of all the pictures in a collection)?
How can I compute a separate result from each of a collection’s element? (E.g., given a vector of person objects, how can I produce a vector of their social security numbers?)
We expect that you’ll find the upcoming methods very convenient. You can use them to write code that is expressive and to-the-point. These methods are especially typical of functional programming (more on which in 11.2), whereas imperative programming had tended to favor loops.
Much of this chapter consists of small examples of API methods. In that respect, we pick up where we left off in Chapter 4.2, which introduced a variety of first-order methods on collections.
For simplicity, many of the examples below feature integer vectors. However, the same methods work for other collection types, too, and for non-integer elements.
Many of the examples use function literals (Chapter 6.2) — both in the full form and abbreviated with underscores — so before you continue, please ensure that you understand those notations.
Repeating an Operation with foreach
In a sense, the most generic of all the higher-order methods on Scala collections is
foreach
. As a first example, let’s use this method to print out the squares of each
number in a collection.
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.foreach( n => println(n * n) )100 25 16 25 400
As its name suggests, foreach
performs the given operation
on each element of the collection. In this case, it computes
the square of each element and prints it out.
Even though the method name contains two English words, it is
(against convention and somewhat confusingly) spelled with a
lower-case E
.
You probably noticed already that foreach
does pretty much the same thing as
repeatForEachElement
, the higher-order function you wrote in Chapter 6.1. The main
difference is that foreach
is a library method available on all collections, and
you can use it in any Scala program.
foreach
expects to be given a function that returns Unit
. Any function that you pass
to foreach
should therefore bring about an effect of some sort, such as printing (as
above) or modifying an object’s state.
Loops vs. methods on collections
As was already mentioned, the methods in this chapter can be used for similar purposes
as loops. This is especially obvious in our first method, foreach
. After all, you
can also write:
for n <- numbers do
println(n * n)
And indeed these two do the same thing:
for element <- elements do Do something with the element.
elements.foreach( element => Do something with the element. )
As a matter of fact, a for
loop such as the above is simply a different way of writing
a foreach
call. The Scala compiler automatically translates it into a method call.
As another example, here is one of the methods from Chapter 5.5’s AuctionHouse
class:
def nextDay() =
for current <- this.items do
current.advanceOneDay()
We could have just as well written:
def nextDay() =
this.items.foreach( _.advanceOneDay() )
Which one is more elegant and easier to read depends on context and on the programmer’s personal taste.
In O1, we’ll use foreach
often, but we’ll continue to use the for
loop as well. Feel
free to use whichever you prefer, but an educated Scala programmer needs to be familiar
with both.
A+ presents the exercise submission form here.
Interlude: Levels of Abstraction
Examining a Collection
Checking properties with exists
and forall
The exists
method is an easy way to determine whether or not any of the elements in
the collection meets a particular criterion:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.exists( _ < 0 )res0: Boolean = true numbers.exists( _ < -100 )res1: Boolean = false
We give exists
a function that takes an element and returns
a Boolean
indicating whether the element meets a particular
condition. Here, for instance, we pass in a function that
determines whether its parameter is a negative number.
Our example collection contains (at least) one negative element. It doesn’t contain even a single element less than -100.
forall
similarly checks whether all the elements of the collection fulfill the given
criterion:
numbers.forall( _ > 0 )res2: Boolean = false numbers.forall( _ > -100 )res3: Boolean = true
In this example, we first checked whether all the elements are positive; they aren’t. Then we determined that all the elements are greater than -100.
Getting to know count
, exists
, and forall
A+ presents the exercise submission form here.
An afterthought
In the question above, why was one of the expressions written like this?
// Version 1 (which works)
elements.forall( !myCriterion(_) )
Couldn’t we have simply written this?
// Version 2 (which doesn't work)
elements.forall( !myCriterion )
As noted in Chapter 6.2, there are different ways to write a function literal. However, Version 2 doesn’t work, because it doesn’t actually define a function literal.
forall
, like many other methods on collections, expects to be given a function
that it can apply to each element in turn. However, the expression !myCriterion
does not refer to any function, not even if there exists a function named myCriterion
.
To pass in the reverse of myCriterion
, you need to formulate a function that
calls myCriterion
and applies the negation operator !
to the result. To that
end, you can either use an underscore, as above, or the full arrow notation, as
below.
// Version 3 (which works)
elements.forall( elem => !myCriterion(elem) )
Selecting Elements from a Collection
Using find
, filter
, takeWhile
, and dropWhile
The find
method goes through the collection and returns the first element it finds that
meets the given criterion. For instance, you could look for the first number that’s less
than five:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.find( _ < 5 )res4: Option[Int] = Some(4)
Notice that find
returns an Option
wrapped around the value that was found. If the
search results in a miss, you get None
:
numbers.find( _ == 100 )res5: Option[Int] = None
filter
is similar to find
except that it returns a collection of all the elements
that match the criterion. Our vector contains four positive numbers:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.filter( _ > 0 )res6: Vector[Int] = Vector(10, 5, 4, 5)
In Chapter 4.2, you saw a take
method that returns a partial collection with the
given number of elements from the beginning of the original collection (say,
numbers.take(3)
). take
’s higher-order cousin is takeWhile
:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.takeWhile( _ >= 5 )res7: Vector[Int] = Vector(10, 5)
As shown above, the method takes elements from the beginning of the collection until it runs into an element that doesn’t meet the given criterion.
A+ presents the exercise submission form here.
filter
vs. filterNot
; takeWhile
vs. dropWhile
Assignment: Reimplementing Election (Part 1 of 2)
This was a good activity. My code is so much shorter now.
In Chapter 5.6, you wrote a number of methods for class District
in module Election.
(If you didn’t, do that now or see the example solution.) At that time,
you (probably) used loops to implement the methods.
Rewrite two of the methods, namely printCandidates
and candidatesFrom
. For each one,
there exists a simple implementation that uses one of the methods introduced above. Use
those methods instead of for
loops.
We’ll get back to the other District
methods later.
A+ presents the exercise submission form here.
Mapping a Collection of Elements: map
and flatMap
It is remarkably often useful to “map” a collection of elements to another.
The higher-order method map
returns a new collection whose elements have been generated
by applying map
’s parameter function to each of original collection’s elements. In the
example below, we use map
to compute each element’s absolute value and obtain a new
vector that contains each of the results in order:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) numbers.map( _.abs )res8: Vector[Int] = Vector(10, 5, 4, 5, 20)
The following expression determines, for each element, whether or not it is at least five. The output vector contains the resulting Booleans in order:
numbers.map( _ >= 5 )res9: Vector[Boolean] = Vector(true, true, false, true, false)
You can use map
in combination with a wide variety of parameter functions. Like the
other methods of this chapter, map
is also available on collections other than
vectors. For instance, you can call it on the Range
object that you get by writing
1 to 10
(Chapter 5.6):
(1 to 10).map( n => n * n )res10: IndexedSeq[Int] = Vector(1, 4, 9, 16, 25, 36, 49, 64, 81, 100)
One more example, this time with Double
s as elements and a named function as a
parameter:
import scala.math.sqrtval data = Vector(100.0, 25.0, 12.3, 2, 1.21)data: Vector[Double] = Vector(100.0, 25.0, 12.3, 2.0, 1.21) data.map(sqrt)res11: Vector[Double] = Vector(10.0, 5.0, 3.5071355833500366, 1.4142135623730951, 1.1)
map
ping the square-root function to each element gives us
a collection with all the roots.
Getting to know map
A+ presents the exercise submission form here.
The flatMap
method
Chapter 6.1 mentioned a method that “flattens” a collection of collections:
val nested = Vector(Vector(3, -10, -4), Vector(5, -10, 1), Vector(-1), Vector(4, 4))nested: Vector[Vector[Int]] = Vector(Vector(3, -10, -4), Vector(5, -10, 1), Vector(-1), Vector(4, 4)) nested.flattenres14: Vector[Int] = Vector(3, -10, -4, 5, -10, 1, -1, 4, 4)
It’s fairly common that we want to first map
a collection to produce a nested
collection, then flatten
the result. Here’s a toy example:
val numbers = Vector(10, 5, 4, 5, -20)numbers: Vector[Int] = Vector(10, 5, 4, 5, -20) val experiment = numbers.map( n => Vector(-n.abs, 0, n.abs) )experiment: Vector[Vector[Int]] = Vector(Vector(-10, 0, 10), Vector(-5, 0, 5), Vector(-4, 0, 4), Vector(-5, 0, 5), Vector(-20, 0, 20)) experiment.flattenres15: Vector[Int] = Vector(-10, 0, 10, -5, 0, 5, -4, 0, 4, -5, 0, 5, -20, 0, 20)
It’s possible to combine map
and flatten
into a single method call:
numbers.flatMap( n => Vector(-n.abs, 0, n.abs) )res16: Vector[Int] = Vector(-10, 0, 10, -5, 0, 5, -4, 0, 4, -5, 0, 5, -20, 0, 20)
That is, collection.flatMap(myFunc)
does the same as collection.map(myFunc).flatten
.
You may well be wondering whether combining map
with flatten
is so useful that
it merits a separate flatMap
method. Yes, it really is. You’ll see as your programming
experience grows during the rest of O1 and later.
Example: users and addresses
For a somewhat more interesting example of map
and flatMap
, consider the following
class.
class User(val id: String, val emailAddresses: Vector[String]):
override def toString = this.id + " <" + this.emailAddresses.mkString(",") + ">"
Let’s imagine we’re working on an application that stores User
objects in a vector. In
the example below, our vector contains just two users, but of course there could be many
more.
val allUsers = Vector( User("sophia", Vector("sophia.student@aalto.fi", "sophia.student@iki.fi", "sophia.student@gmail.com")), User("megadestroyer", Vector("teemu.teekkari@aalto.fi", "teemuteekkari@gmail.com")) )allUsers: Vector[User] = Vector(sophia <sophia.student@aalto.fi,sophia.student@iki.fi,sophia.student@gmail.com>, megadestroyer <teemu.teekkari@aalto.fi,teemuteekkari@gmail.com>)
How can we now get a list of all the id
s of all the users? What about a list of all
the email addresses of all the users?
Sure, we could write a loop, but the just-introduced methods get the job done with minimal effort.
The map
method gives us each user’s identifier if we pass in a function that maps a
user object to its id
.
allUsers.map( _.id )res17: Vector[String] = Vector(sophia, megadestroyer)
We can also use map
to access the email addresses. This gives us a nested collection
(which, depending on our purposes, may or may not be convenient):
allUsers.map( _.emailAddresses )res18: Vector[Vector[String]] = Vector(Vector(sophia.student@aalto.fi, sophia.student@iki.fi, sophia.student@gmail.com), Vector(teemu.teekkari@aalto.fi, teemuteekkari@gmail.com))
Assuming we want a single “flat” collection of all the emails, we can use flatMap
instead:
allUsers.flatMap( _.emailAddresses )res19: Vector[String] = Vector(sophia.student@aalto.fi, sophia.student@iki.fi, sophia.student@gmail.com, teemu.teekkari@aalto.fi, teemuteekkari@gmail.com)
The next programming assignment is not only about methods on collections, but it does provide opportunities to use them.
Assignment: Snake
Snake is a classic computer game that originates from the 1970s. The player controls a “snake” or “worm” that turns about on a two-dimensional field, looking to eat and grow. In the 1990s, Snake renewed its popularity as a mobile game, which has in turn attracted nostalgic attention in recent years. By the time you read this, the game may have already reverted to passé retro kitch.
Snake is also a classic as a programming exercise. Let us join the tradition.
Concepts in Snake
The key components of a game of Snake are the snake itself and the food that the snake seeks to swallow. At any given moment, there is a single item of food available for the snake, located somewhere on the playing field. When the snake eats the food — that is, when the snake’s head is about to hit it — the snake grows and a new item of food appears.
You can think of the playing field as a grid (see image). The food is located in a single space on the grid. The snake consists of segments (“pieces”), each of which takes up a space.
The only thing the player can do is press one of the arrow keys to make the snake turn in that direction. The snake can move only in the four main compass directions.
As time passes, the snake moves step by step: its first segment, or “head”, moves in the latest direction chosen by the player and the other segments follow (see the second image). However, if the head enters the food space, the snake eats the food and grows by a single segment: a new segment appears where the food was and all the other segments remain where they were.
The game is over when the snake’s head hits something other than food.
Classes in Snake
The Snake module contains a partial implementation for the game. The overall design
of the program resembles that of FlappyBug: we have a SnakeGame
class that represents
the mutable state of a game and a GUI (in SnakeApp.scala
) that displays the state and
receiving commands from the player.
So, an instance of SnakeGame
represents a single session of Snake. Calling that
instance’s methods changes its state. The SnakeGame
object tracks:
the next item of food: where is it on the grid?
the location of the snake: where on the grid are its segments?
the direction of the (head of the) snake: which of the four compass directions has it been ordered to go?
Our class needs to manipulate locations on the grid as well as directions. For that, we
have tools on hand in package o1
:
The classes GridPos
and CompassDir
Class GridPos
represents coordinates on a grid. Each coordinate is an integer.
This class resembles the
Pos
you know but is specifically designed for use with grids and provides some convenient methods to that end.We therefore distinguish between two things: which space something is located at (
GridPos
), and which spot within a particular image something should be drawn at (Pos
).The
GridPos
is part of the program domain’s internal logic (i.e., the rules of Snake). ThePos
is a feature of the GUI.This is similar to what we did in the Stars module, where we distinguished between a
StarCoords
on a map and aPos
within an image.
The class CompassDir
represents compass directions such as north (up) and
west (left):
It’s well suited for representing the snake’s heading.
It combines well with the methods on
GridPos
. For instance, we can ask aGridPos
object which coordinates neighbor it in a particular direction.
Both classes are documented within the O1Library module.
A couple of mini-assignments as groundwork
The answers to these questions should help you along as you tackle the main task of implementing the snake game.
A+ presents the exercise submission form here.
A+ presents the exercise submission form here.
The main task
In SnakeGame.scala
and SnakeApp.scala
, find the locations where something is missing
and implement the missing parts. We suggest that you proceed as follows.
Step 0 of 5: preparations
Run the given program. You should see a playing field with a food item and a single-segment snakeling. (There is no visible grid like in the illustrations above; that’s intentional.) The snake doesn’t move yet.
Study class SnakeGame
. Observe that there are parts missing. Note how the given code uses
the classes GridPos
and CompassDir
. In the Scaladocs for those other classes, read at
least the introductions at the top; there’s no need to wade through all the methods. (The
Snake module itself has no Scaladocs. All the information you need is in this chapter and
in the Scala code.)
You may want to take a look at SnakeApp.scala
, too. As the clock ticks, the GUI calls
the advance
method of the appropriate SnakeGame
object. advance
is supposed to
move the snake. The given version doesn’t do anything, however.
Step 1 of 5: a mobile snake
For now, write a partial implementation for advance
: make it move the snake’s head to
the next space. Don’t worry about growing the snake yet.
Hints:
The
segments
variable refers to a single-element vector that contains the location of the (head of the) snake. This is avar
. Replace its value with a single-element vector containing the neighboring location towards the current heading.There is a convenient method in
GridPos
for determining that location.
Run the modified program. See the single segment slither.
The game ends when the snake hits an edge. You control the snake with the arrow keys (or WASD). The snake ignores the food.
Step 2 of 5: snake snacks
Develop advance
further. The method must now additionally move the food into a new
random location whenever the snake hits it. That relocation of the food happens as part
of the same movement step (i.e., the same call to advance
) that puts the snake’s only
segment in the current food space. The advance
method should first move the snake,
then the food; the food is moved only in case the snake found the food at its current
location.
You can do that by updating the value of the nextFood
variable. Use the given method
randomEmptyLocation()
to pick a new location. (The method is defined on SnakeGame
.
You don’t have to understand its implementation now; it’s enough to call it and use the
GridPos
that it returns.)
Try running your program. Food gets eaten, but the snake doesn’t grow.
There’s a GameSpeed
constant in SnakeApp.scala
. You may adjust it to your liking. You
could slow down the game while testing, for instance.
Step 3 of 5: a growing snake
In this step, you’ll make the snake grow (although the growth won’t visible onscreen just yet).
Finish up advance
. Each time the method is called, the snake either eats (and grows)
or moves, but not both. In other words: 1) when the head is just about to hit the food,
add a segment; 2) otherwise, move the snake but don’t add a segment.
Earlier, we assumed that the segments
vector always holds just one single element.
This assumption no longer holds.
In Step 1 above, you wrote a line of code that replaces the value of segments
with a
new single-element vector. Remove that line. In its place, write some new code to handle
both of the cases: the head either finds food, or doesn’t.
That is, replace the value of segments
with a new vector that contains all the snake’s
locations after the move. There should be either exactly as many segments as before, or
one more.
Instructions and hints:
Grow the snake from the front. When the snake’s head would end up moving to a food square, don’t move the snake at all. Instead, add a new segment where the food is; it becomes the snake’s new head. (The frontmost segment becomes the second-from-front. All existing segments stay where they are. See the illustration on the right.)
The food must be relocated as part of the same
advance
call that brings the snake’s head to where the food is. (When anadvance
call ends, the food is never where the Snake’s head is.)To form the new vector, you can use the tools from 4.2, which were just revisited in the mini-assignment above.
The segments are identical. You don’t have to move each segment separately. All the middle segments remain within the snake: if you take care of the first and last segments, that’s enough to create the illusion of movement.
You may choose to reveal the additional hint below.
Hint for moving the snake segments
When the snake advances without eating, you need to construct a vector that contains the head’s new location followed by all the snake’s earlier locations except the last. The solution is fundamentally identically with what you did with an
Int
vector in the preceding mini-assignment.Also remember that just creating a vector doesn’t store the vector anywhere. You’ll need to do that explicitly.
Try running your program after you complete this step. The snake still doesn’t seem to grow. In fact, it does grow, but you don’t see it because the GUI draws only the head.
Step 4 of 5: sorting out the graphics
Turn to the GUI in SnakeApp.scala
and the makePic
method defined there. Observe:
The method places only a single copy of
SegmentPic
(reddish picture of a snake segment) against the background.makePic
uses an auxiliary functiontoPixelPos
, which is defined in the same file. That function takes in aGridPos
and determines where in the GUI image that space should be drawn.makePic
also uses aplaceCopies
method from classPic
. As its first parameter, that method takes a picture. As its second parameter, it takes a vector ofPos
objects. That method works just like the familiarplace
method, except that it places multiple copies of the same image. Which doesn’t help much yet, since the given code passes in only a single-element vector.
Edit makePic
so that it draws all the segments as identical round shapes. Here’s how:
Use
toPixelPos
to determine each segment’s position within the image. You don’t need a loop. Use one of the collection methods from this chapter.Call
placeCopies
, passing in a vector that contains aPos
for each segment.
The snake grows!
Step 5 of 5: collisions
It is ordained by the tradition of snake gaming that snakes die if they collide with their
own body. Attend to this in class SnakeGame
: the isOver
method should indicate that
the game is over not only when the snake hits a wall but also if its head shares a location
with any of the other segments. (That is, the game is over when the head is already in
the same location as another segment, not before.)
You can again turn to Chapter 4.2 for tooling.
Additional hint
The snake has a head and a tail. Your method should determine whether the head’s location is among the tail’s locations — that is, whether the tail contains the head. As noted, the tools for doing just that are in Chapter 4.2.
A special case
What should happen when a two-segment snake turns 180 degrees? Does its head segment collide with the single tail segment or not? Or maybe the snake should be prevented from doing that altogether? You choose. The automatic tests for this assignment don’t test that case.
A+ presents the exercise submission form here.
Summary of Key Points
The collection classes of the Scala API define a whole bunch of higher-order methods that operate on the elements of collections.
Methods in common use include
foreach
,exists
,forall
,find
,filter
,map
, andflatMap
. You’ll see more later.These methods provide generic solutions to common problems and are often a convenient alternative to loops.
Processing collections in this manner is especially common in so-called functional programming, which Scala encourages.
Links to the glossary: higher-order function; collection; level of abstraction.
Why This Chapter Matters
We’ll make frequent use of the methods introduced above. They will serve you well in upcoming programming assignments.
You’ll need to read a lot of given code that uses these methods.
You may initially struggle to recall each method. Then again, you don’t need to. You can return to this chapter for reference, or use our Scala Reference.
The important thing for now is to bear in mind the general idea: there is a wide selection of convenient higher-order methods on offer.
Bonus teaser about for
–yield
expressions
It’s already come up in the ebook that the for
–do
loops that
we’ve written are just another way of writing a foreach
method
call. These two do the same thing:
numbers.foreach( n => println("The square is " + n * n) )
for n <- numbers do
println("The square is " + n * n) )
Scala’s for
construct can be used for a bunch of other things,
too. (But you don’t have to in O1.) For instance, you can write
a map
method call as a for
expression. These two do the same
thing:
val squares = numbers.map( n => n * n )
val squares = for n <- numbers yield n * n
yield
is a reserved word that you can
use to make a for
expression produce a
result other than Unit
.
And below, you’ll find a flatMap
call and a for
–yield
structure that’s equivalent to it. Both code fragments traverse a
numbers
vector twice and produce all possible two-element sums:
val sums = for first <- numbers; second <- numbers yield first + second
val sums = numbers.flatMap( first => numbers.map( second => first + second ) )
You may split a for
–yield
expression across multiple lines.
Here’s one way to do that:
val sums =
for
first <- numbers
second <- numbers
yield first + second
Feedback
Please note that this section must be completed individually. Even if you worked on this chapter with a pair, each of you should submit the form separately.
Credits
Thousands of students have given feedback and so contributed to this ebook’s design. Thank you!
The ebook’s chapters, programming assignments, and weekly bulletins have been written in Finnish and translated into English by Juha Sorva.
The appendices (glossary, Scala reference, FAQ, etc.) are by Juha Sorva unless otherwise specified on the page.
The automatic assessment of the assignments has been developed by: (in alphabetical order) Riku Autio, Nikolas Drosdek, Kaisa Ek, Joonatan Honkamaa, Antti Immonen, Jaakko Kantojärvi, Niklas Kröger, Kalle Laitinen, Teemu Lehtinen, Mikael Lenander, Ilona Ma, Jaakko Nakaza, Strasdosky Otewa, Timi Seppälä, Teemu Sirkiä, Anna Valldeoriola Cardó, and Aleksi Vartiainen.
The illustrations at the top of each chapter, and the similar drawings elsewhere in the ebook, are the work of Christina Lassheikki.
The animations that detail the execution Scala programs have been designed by Juha Sorva and Teemu Sirkiä. Teemu Sirkiä and Riku Autio did the technical implementation, relying on Teemu’s Jsvee and Kelmu toolkits.
The other diagrams and interactive presentations in the ebook are by Juha Sorva.
The O1Library software has been developed by Aleksi Lukkarinen and Juha Sorva. Several of its key components are built upon Aleksi’s SMCL library.
The pedagogy of using O1Library for simple graphical programming (such as Pic
) is
inspired by the textbooks How to Design Programs by Flatt, Felleisen, Findler, and
Krishnamurthi and Picturing Programs by Stephen Bloch.
The course platform A+ was originally created at Aalto’s LeTech research group as a student project. The open-source project is now shepherded by the Computer Science department’s edu-tech team and hosted by the department’s IT services. Markku Riekkinen is the current lead developer; dozens of Aalto students and others have also contributed.
The A+ Courses plugin, which supports A+ and O1 in IntelliJ IDEA, is another open-source project. It has been designed and implemented by various students in collaboration with O1’s teachers.
For O1’s current teaching staff, please see Chapter 1.1.
Additional credits appear at the ends of some chapters.
foreach
takes in a function that takes in a single element (here: anInt
), such as the anonymous function that we have in this example.