Think Julia

Chapter 4. Case Study: Interface Design

This chapter presents a case study that demonstrates a process for designing functions that work together.

It introduces turtle graphics, a way to create programmatic drawings. Turtle graphics are not included in the standard library, so to use them you’ll have to add the ThinkJulia module to your Julia setup.

The examples in this chapter can be executed in a graphical notebook on JuliaBox, which combines code, formatted text, math, and multimedia in a single document (see Appendix B).

Turtles

A module is a file that contains a collection of related functions. Julia provides some modules in its standard library. Additional functionality can be added from a growing collection of packages.

Packages can be installed in the REPL by entering the Pkg REPL mode using the key ] and using the add command:

(v1.0) pkg> add https://github.com/BenLauwens/ThinkJulia.jl

This can take some time.

Before we can use the functions in a module, we have to import it with a using statement:

julia> using ThinkJulia

julia> 🐢 = Turtle()
Luxor.Turtle(0.0, 0.0, true, 0.0, (0.0, 0.0, 0.0))

The ThinkJulia module provides a function called Turtle that creates a Luxor.Turtle object, which we assign to a variable named 🐢(\:turtle: TAB).

Once you create a turtle, you can call a function to move it around. For example, to move the turtle forward:

@svg begin
    forward(🐢, 100)
end

The @svg keyword runs a macro that draws an SVG picture (Figure 4-1). Macros are an important ...