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Crystal

Crystal - Programming language

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Crystal is an open source programming language created in 2014 by Ary Borenszweig and Juan Wajnerman and Brian Cardiff.

Source code:
git clone https://github.com/crystal-lang/crystal
#61on PLDB 9Years Old 8kRepos

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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...


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"
# 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
Crystal Keywords
abstract do if nil? self unless alias else in of sizeof until as elsif include out struct when as? end instance_sizeof pointerof super while asm ensure is_a? 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

Language features

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

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