Macros

Metaprogramming

Julia code is itself data and can be manipulated by the language while it is running

Large influence from Lisp
Since Julia is entirely written in Julia, it is particularly well suited for metaprogramming

Let’s start with something simple:

2 + 3

How is this run internally?

The string "2 + 3" gets parsed into an expression:

Meta.parse("2 + 3")

Then that expression gets evaluated:

eval(Meta.parse("2 + 3"))

They resemble functions and just like functions, they accept as input a tuple of arguments

BUT macros return an expression which is compiled directly rather than requiring a runtime eval call

So they execute before the rest of the code is run

Macro’s names are preceded by @ (e.g. @time)

Julia comes with many macros and you can create your own with:

macro <name>()
    <body>
end