Module 1: Values, Tuples and Pattern Matching

Introduction

As you have never programmed before we will start slowly.

Livebook is an interactive development environment that is accessed through a browser. You work is organized in notebooks which are physically stored on the machine that hosts Livebook. You have now seen two of these; first the Start one and then this Module 1 one. If such a notebook is associated with a filename then it will be automatically saved. You can make sure this is the case by ckicking on the disk/save icon in the lower right corner of this screen. No need to do it for this notebook though, as it has already been done.

A notebook is structured in sections. In each such section one can place cells with markdown code (such as this one), Elixir code or a few other things. Markdown is a form of structured text. If you click this text and click the edit icon that then appears above it to the right, you can edit the text.

When you move the mouse in between two cells you will be presented with a number of options for adding a cell. When the mouse overs over an existing cell you will be presented with options for interacting with this cell. An Elixir cell, for instance, can be evaluated by pressing ➤ Evaluate just above the cell to the left.

Preparation

Values and Expressions

All valid Elixir code will evaluate to a value. Here are a few simple examples:

"Hello, World"

42

1+2

:math.pi

Tuples

Data can be organized in tuples. This is a form of data structure that represents a sequence of a fixed number of values. A tuple can be treated as a single value even if it contains multiple values. Here are a few examples of tuples:

{1,2}

{1,2,3}

{"a", 1}

{1,{2,3}}

Pattern matching

Elixir has a match operator = which attempts to bind whatever is at the left-hand side of the operator to the value that the expression on the right-hand side of it evaluates to. This is typically used for two purposes:

1. To check that something is the case. For instance, to check that a value has a specific structure. Here, you can use the _ character to mark elements that you have no need to refer to.
2. To bind variable names to parts of a structure. This means that a name is introduced (that we can refer to at a later point in the code), and that this name is associated with a value.

A few examples:

pi = :math.pi

pi

t = {1, 2}

{42, {tx, _}} = {42, t}

tx

{x, _y} = t

x

_y

That last one should produce a warning stating that Elixir does not know about the variable _y. This is because it starts with an underscore character and thus hasn’t been bound on the line where x was bound.

Exercise

A circle has a diameter of $30.9$:

d = 30.9

Calculate the radius (by dividing the value of d by two) and bind the variable r to the result of this calculation:

r = d/2

A circle with radius $r$ has the circumference $2 \pi r$. Calculate the circumference of the circle in the following cell:

c = 2*:math.pi*r

To the right of the ➤ Evaluate button, you will find a drop-down menu. This menu contains an option for automatically evaluating a cell when the contents of the previous code cell has changed.

Now, you should:

1. Make sure the two previous Elixir cells are configured to automatically evaluate.
2. Change the definition of d in the above cell to have the value :math.pi.
3. Observe the result of the previous cell.

Next step …

Good, we have now covered the basics. Lets continue with the next exercise here.