Crystal

Crystal is a programming language created in 2014 by Ary Borenszweig.

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In computer software programming languages, Crystal is a general-purpose, object-oriented programming language, designed and developed by Ary Borenszweig and Juan Wajnerman and more than 200 contributors. With syntax inspired by the language Ruby, it is a compiled language with static type-checking, but specifying the types of variables or method arguments is generally unneeded. Types are resolved by an advanced global type inference algorithm. Read more on Wikipedia...

Crystal website
Crystal Wikipedia page
Crystal is developed on GitHub and has 17,909 stars
PLDB has 2 documentation sites for Crystal: crystal-lang.org, devdocs.io
There are at least 7,522 Crystal repos on GitHub
Crystal first developed in https://forum.crystal-lang.org/
file extensions for Crystal include cr
Crystal on Twitter
The Google BigQuery Public Dataset GitHub snapshot shows 767 users using Crystal in 1k repos on GitHub
There are 4,118 members in the Crystal subreddit
There are 14 Project Euler users using Crystal
In the 2021 StackOverflow developer survey Crystal programmers reported a median salary of $72,400. 1% of respondents reported using Crystal. 466 programmers reported using Crystal, and 790 said they wanted to use it
Explore Crystal snippets on Rosetta Code
Crystal ranks #24 in the TIOBE Index
Crystal LSP implementation
Pygments supports syntax highlighting for Crystal
GitHub supports syntax highlighting for Crystal
Official Blog page for Crystal
Frequently Asked Questions for Crystal
crystal-lang.org was registered in 2013
See also: (10 related languages)IA-32, FreeBSD, Ruby, C, Rust, Go, C#, Python, LLVM IR, CSP
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Example from Compiler Explorer:

# Type your code here, or load an example.

# compile with --prelude=empty
fun square(num : Int32) : Int32
  num &* num
end

Example from Riju:

puts "Hello, world!"

Example from hello-world:

puts "Hello World"

Example from the Hello World Collection:

# Hello world in Crystal

puts "Hello World"

Example from Linguist:

#!/usr/bin/env bin/crystal --run
require "../../spec_helper"

describe "Type inference: declare var" do
  it "types declare var" do
    assert_type("a :: Int32") { int32 }
  end

  it "types declare var and reads it" do
    assert_type("a :: Int32; a") { int32 }
  end

  it "types declare var and changes its type" do
    assert_type("a :: Int32; while 1 == 2; a = 'a'; end; a") { union_of(int32, char) }
  end

  it "declares instance var which appears in initialize" do
    result = assert_type("
      class Foo
        @x :: Int32
      end

      Foo.new") { types["Foo"] }

    mod = result.program

    foo = mod.types["Foo"] as NonGenericClassType
    foo.instance_vars["@x"].type.should eq(mod.int32)
  end

  it "declares instance var of generic class" do
    result = assert_type("
      class Foo(T)
        @x :: T
      end

      Foo(Int32).new") do
        foo = types["Foo"] as GenericClassType
        foo_i32 = foo.instantiate([int32] of Type | ASTNode)
        foo_i32.lookup_instance_var("@x").type.should eq(int32)
        foo_i32
    end
  end

  it "declares instance var of generic class after reopen" do
    result = assert_type("
      class Foo(T)
      end

      f = Foo(Int32).new

      class Foo(T)
        @x :: T
      end

      f") do
        foo = types["Foo"] as GenericClassType
        foo_i32 = foo.instantiate([int32] of Type | ASTNode)
        foo_i32.lookup_instance_var("@x").type.should eq(int32)
        foo_i32
    end
  end

  it "declares an instance variable in initialize" do
    assert_type("
      class Foo
        def initialize
          @x :: Int32
        end

        def x
          @x
        end
      end

      Foo.new.x
      ") { int32 }
  end
end

Example from Wikipedia:

channel = Channel(Int32).new

spawn do
  puts "Before first send"
  channel.send(1)
  puts "Before second send"
  channel.send(2)
end

puts "Before first receive"
value = channel.receive
puts value # => 1

puts "Before second receive"
value = channel.receive
puts value # => 2

Keywords in Crystal

abstract do if nil? self unless alias else in of sizeof until as elsif include out struct when as? end instancesizeof pointerof super while asm ensure isa? private then with begin enum lib protected true yield break extend macro require type case false module rescue typeof class for next return uninitialized def fun nil select union

Feature	Supported	Token	Example
While Loops	✓
Conditionals	✓
Functions	✓
Classes	✓
File Imports	✓	require	require "../../spec_helper"
Booleans	✓	true false
Strings	✓	"	"Hello world"
Print() Debugging	✓	puts
Comments	✓		# A comment
Line Comments	✓	#	# A comment
Type Inference	✓
Semantic Indentation	X
MultiLine Comments	X

title	authors	year	publisher
Crystal Clear: A Human-Powered Methodology for Small Teams: A Human-Powered Methodology for Small Teams	Cockburn, Alistair and Paul Becker, Alistair	2004	Addison-Wesley Professional
Crystal Reports .net Programming	Bischof and Brian	2004	Bischof Systems
Crystal Reports Professional Results	Peck, George	2003	McGraw-Hill Education
Crystal Programming: A project-based introduction to building efficient, safe, and readable web and CLI applications	Dietrich, George and Bernal, Guilherme	2022	Packt Publishing
Crystal Reports XI Official Guide	Fitzgerald, Neil and et al.	2006	Sams Publishing

title	authors	year	citations	influentialCitations
Crystal engineering with DNA	Christine R Laramy and Matthew N. O’Brien and C. Mirkin	2019	103	1
FOX: Modular Approach to Crystal Structure Determination from Powder Diffraction	V. Favre-Nicolin and R. Černý	2004	34	0
Crystal Gazer	Shoaib Akram and Jennifer B. Sartor and K. McKinley and L. Eeckhout	2019	7	0
Crystal Reference Manual Version 3.0	M. Jacquemin and J. A. Yang	1991	3	0
3DStructGen: an interactive web-based 3D structure generation for non-periodic molecule and crystal	Pin Chen and Yu Wang and Hui Yan and Sen Gao and Zexin Xu and Yangzhong Li and Qing Mo and Junkang Huang and Jun Tao and Gechuanqi Pan and Jiahui Li and Yunfei Du	2020	2	0
Simulation of a micro-milling single crystal copper process based on crystal plastic constitutive theory	Luan Yihan and Meng Xiangyue and Xue Liang and S. Liang and L. Xiaohong	2020	1	0

Keywords in Crystal

Language features

Books about Crystal from ISBNdb

Publications about Crystal from Semantic Scholar