The Crystal Programming Language

# A very basic HTTP server require "http/server" server = HTTP::Server.new do |context| context.response.content_type = "text/plain" context.response.print "Hello world, got #{context.request.path}!" end address = server.bind_tcp(8080) puts "Listening on http://#{address}" # This call blocks until the process is terminated server.listen

require "http/client" require "json" response = HTTP::Client.get("https://crystal-lang.org/api/versions.json") json = JSON.parse(response.body) version = json["versions"].as_a.find! { |entry| entry["released"]? != false }["name"] puts "Latest Crystal version: #{version || "Unknown"}"

loop do case message = gets # type is `String | Nil` when Nil break when "" puts "Please enter a message" else # In this branch, `message` cannot be `Nil` so we can safely call `String#upcase` puts message.upcase end end

channel = Channel(Int32).new 3.times do |i| spawn do 3.times do |j| sleep rand(100).milliseconds # add non-determinism for fun channel.send 10 * (i + 1) + j end end end 9.times do puts channel.receive end

# Define the lib bindings and link info: @[Link("m")] lib LibM fun pow(x : LibC::Double, y : LibC::Double) : LibC::Double end # Call a C function like a Crystal method: puts LibM.pow(2.0, 4.0) # => 16.0

macro upcase_getter(name) def {{ name.id }} @{{ name.id }}.upcase end end class Person upcase_getter name def initialize(@name : String) end end person = Person.new "John" person.name # => "JOHN"