var = 1
$foo = Proc.new { var }
var = 2

def foo
 $foo.call
end

p foo    # => 2

def foo
 proc { return }
end

foo.call
# => in `call': return from proc-closure (LocalJumpError)

def foo
 proc { retry }
end

foo.call
# => in `call': retry from proc-closure (LocalJumpError)

# 没问题
(1..5).each { break }

# 在ruby 1.6.7, 1.8中没问题。在1.6.8中则发生异常
proc = Proc.new { break }
(1..5).each(&proc)

# 在ruby 1.6 中是 LocalJumpError
# 在ruby 1.8 中，再次运行each
proc = Proc.new { retry }
(1..5).each(&proc)
#=> retry from proc-closure (LocalJumpError)

Proc.new
Proc.new { ... }

def foo
  pr = Proc.new
  pr.call(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]

def foo
  pr = Proc.new
  pr.call(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]
这与下例相同
def foo
 yield(1,2,3)
end
foo {|args| p args }
# => [1, 2, 3]

def foo
 Proc.new
end
foo
# => -:2:in `new': tried to create Proc object without a block (ArgumentError)
     from -:2:in `foo'
     from -:4

# 判断西历的年是否为闰年的处理
leap = Proc.new do |year|
 year % 4 == 0 && year % 100 != 0 || year % 400 ==0
end
　
p leap.call(2000)  #=> true
p leap[2013]     #=> false
p leap[2016]     #=> true

double = Proc.new do |*args|
 args.map{|i| i * 2 }  # 所有元素乘两倍
end
　
p double.call(1, 2, 3)  #=> [2, 3, 4]
p double[2, 3, 4]     #=> [4, 6, 8]