October 2014
Intermediate to advanced
280 pages
7h 20m
English
Content preview from Programming Elixir
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Macros Are Hygienic
It is tempting to think of macros as some kind of textual substitution—a macro’s body is expanded as text and then compiled at the point of call. But that’s not the case. Consider this example:
| macros/hygiene.ex | |
| | defmodule Scope do |
| | defmacro update_local(val) do |
| | local = "some value" |
| | result = quote do |
| | local = unquote(val) |
| | IO.puts "End of macro body, local = #{local}" |
| | end |
| | IO.puts "In macro definition, local = #{local}" |
| | result |
| | end |
| | end |
| | defmodule Test do |
| | require Scope |
| | |
| | local = 123 |
| | Scope.update_local("cat") |
| | IO.puts "On return, local = #{local}" |
| | end |
Here’s the result of running that code:
| | In macro definition, local = some value |
| | End of macro body, local = cat |
| |
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.