From: Eric Hodel <drbrain@...7.net>
Date: 2003-08-06T16:53:16-07:00
Subject: Re: Why does Ruby have callcc?


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Eric Hodel (drbrain@segment7.net) wrote:

> Ben Giddings (ben@thingmagic.com) wrote:
>=20
> > Is there some reason that Continuation.new couldn't work?
>=20
> I don't know if this is 100% correct:
>=20
> class Continuation
>   def self.new
>     if block_given? then
>       callcc { |c| yield(c) }
>     else
>       callcc { |c| return c }
>     end
>   end
> end

Oh yes, and there is this problem:

irb(main):007:0> c =3D Continuation.new; puts 'hi'
hi
=3D> nil
irb(main):008:0> c.call
hi
=3D> nil
irb(main):009:0> c.call
NoMethodError: undefined method `call' for nil
        from (irb):9

Which is easily avoided with the block:

irb(main):012:0> cx =3D nil
=3D> nil
irb(main):013:0> callcc { |c| cx =3D c }; puts 'hi'
hi
=3D> nil
irb(main):014:0> cx.call
hi
=3D> nil
irb(main):015:0> cx.call
hi
=3D> nil
irb(main):016:0> cx.call
hi
=3D> nil

The block makes this easy.

--=20
Eric Hodel - drbrain@segment7.net - http://segment7.net
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