callcc Semantics

[Bill Atkins]

What is the purpose of the block passed to callc? Is there a reason
that callcc doesn't just return the Continuation object?

Bill

 

[Mikael Brockman]

What is the purpose of the block passed to callc? Is there a reason
that callcc doesn't just return the Continuation object?

The block isn't part of the continuation. Try writing

| catch :break do
| callcc do |$k|
| puts 'hello'
| throw :break
| end
| puts 'world'
| end

using only returncc.

 

[Eric Hodel]

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What is the purpose of the block passed to callc? Is there a reason
that callcc doesn't just return the Continuation object?

This has been discussed at least once in the past, see the ruby-talk
email archives:

http://www.google.com/search?q=3Dsite:ruby-talk.org+callcc

I will say that call-with-current-continuation cannot work without the
block passed to it. IOW, call (this block of code) with the current
continuation (which gets passed to it as an argument).

x =3D callcc do |cc| ... end
^^
Here || is the "current continuation" for callcc. Without the block,
you can't return here and not do whatever was done in the block. This
is very important, without it you can't do much truly interesting stuff.

--=20
Eric Hodel - (e-mail address removed) - http://segment7.net
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