Crystal 编译型的编程语言

Crystal 是一个编译型的编程语言。特性：

• 语法类似 Ruby Ruby-inspired syntax.

• 无需指定变量类型和方法参数类型 Never have to SPEcify the type of a variable or method argument.

• 可以调用 C 代码 Be able to call C CODE by writing BINDings to it in Crystal.

• 编译时代码模拟和生成 Have comPILe-time evaLuation and geneRATion of code, to avoid Boilerplate code.

• 编译成高效的本机代码 Compile to efficIEnt native code.

示例代码：

# Compute prime numbers up to 100 with the Sieve of Eratosthenes
max = 100
 
sieve = Array.new(max + 1, true)
sieve[0] = false
sieve[1] = false
 
(2...max).each do |i|
  if sieve[i]
    (2 * i).step(max, i) do |j|
      sieve[j] = false
    end
  end
end
 
sieve.each_with_index do |prime, number|
  puts number if prime
end