Book Image

Julia 1.0 Programming. - Second Edition

By : Ivo Balbaert
Book Image

Julia 1.0 Programming. - Second Edition

By: Ivo Balbaert

Overview of this book

The release of Julia 1.0 is now ready to change the technical world by combining the high productivity and ease of use of Python and R with the lightning-fast speed of C++. Julia 1.0 programming gives you a head start in tackling your numerical and data problems. You will begin by learning how to set up a running Julia platform, before exploring its various built-in types. With the help of practical examples, this book walks you through two important collection types: arrays and matrices. In addition to this, you will be taken through how type conversions and promotions work. In the course of the book, you will be introduced to the homo-iconicity and metaprogramming concepts in Julia. You will understand how Julia provides different ways to interact with an operating system, as well as other languages, and then you'll discover what macros are. Once you have grasped the basics, you’ll study what makes Julia suitable for numerical and scientific computing, and learn about the features provided by Julia. By the end of this book, you will also have learned how to run external programs. This book covers all you need to know about Julia in order to leverage its high speed and efficiency for your applications.
Table of Contents (17 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Evaluation and interpolation


With the definition of type Expr from the preceding section, we can also build expressions directly from the constructor for Expr. For example: e1 = Expr(:call, *, 3, 4) returns :((*)(3, 4)) (follow along with the code in Chapter 7\eval.jl).

The result of an expression can be computed with the eval function, eval(e1), which returns 12 in this case. At the time an expression is constructed, not all the symbols have to be defined, but they have to be defined at the time of evaluation, otherwise an error occurs.

For example, e2 = Expr(:call, *, 3, :a) returns :((*)(3, a)), and eval(e2) then gives ERROR: UndefVarError: a not defined. Only after we say, for example, a = 4 does eval(e2) return 12.

Expressions can also change the state of the execution environment, for example, the expression e3 = :(b = 1) assigns a value to b when evaluated, and even defines b, if it doesn't exist already.

 

To make writing expressions a bit simpler, we can use the $ operator to do interpolation...