pat.cr

module Pat
  macro match(&block)
    case {{block.body.cond}}
    {% for whens in block.body.whens %}
      {% if whens.conds.first.is_a?(Cast) %}
        when {{whens.conds.first.to}}
          {{whens.conds.first.obj}} = {{block.body.cond}}
          {{whens.body}}
      {% elsif whens.conds.first.is_a?(ArrayLiteral) %}
        when {{block.body.cond}}.is_a?(Array) && {{block.body.cond}}.as(Array).size == {{whens.conds.first.size}}
          {{whens.body}}
      {% else %}
        when {{whens.conds.first}} 
          {{whens.body}}
        {% end %}
    {% end %}
      else
        {{block.body.else}}
    end
  end
end

include Pat

def foo(x : String|Int|Array(String|Int))
  match {
    case x
    when y.as(String) # introduces a new variable y : String
      puts "String = #{y}"
    when 1
      puts "one"
    else
      puts "Int = #{x}"
    end
  }
end
foo "a"
foo 1
foo 10