From: Mick Macamhlaoibh <mick.macamhlaoibh@...>
Date: 2007-08-14T10:11:17+09:00
Subject: Can a lambda or Proc object yield a value to a block?

I've searched quite a bit on the web and through "Programming Ruby - the
Pragmatic Programmer's Guide" and I can't find a satisfactory answer to
the question:

Can a lambda or Proc object yield a value to a block?

For example when I try this
  yieldArg = lambda {|arg| yield arg}
  yieldArg.call(23) {|y| puts("y="+y.to_s)}
in Interactive Ruby I get
  "LocalJumpError: no block given"

So I try
   yieldArg = lambda {|arg| puts "no block given" unless block_given? ;
yield arg}
to print some indication of whether the block really has been "given"
and I get
  no block given
  LocalJumpError: no block given

So then I try to wrap the block in a lambda and pass it as a param
   putsY = lambda {|y| puts("y="+y.to_s)}
   yieldArg.call(23) {|y| puts("y="+y.to_s)}
   yieldArg.call(23, &putsY)
but with the same negative result.

So can a lambda or Proc object yield a value to a block? If so, how is
it done?

Thanks in advance.

Interactive Ruby session shown below.

irb(main):001:0>  yieldArg = lambda {|arg| yield arg}
=> #<Proc:0x02dfebf0@(irb):1>
irb(main):002:0> yieldArg.call(23) {|y| puts("y="+y.to_s)}
LocalJumpError: no block given
        from (irb):1
        from (irb):2:in `call'
        from (irb):2
irb(main):003:0> yieldArg = lambda {|arg| puts "no block given" unless
block_given? ; yield arg}
=> #<Proc:0x02df58e8@(irb):3>
irb(main):004:0> yieldArg.call(23) {|y| puts("y="+y.to_s)}
no block given
LocalJumpError: no block given
        from (irb):3
        from (irb):4:in `call'
        from (irb):4
irb(main):005:0> putsY = lambda {|y| puts("y="+y.to_s)}
=> #<Proc:0x02dede2c@(irb):5>
irb(main):006:0> yieldArg.call(23, &putsY)
no block given
LocalJumpError: no block given
        from (irb):3
        from (irb):6:in `call'
        from (irb):6
irb(main):007:0>
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