Continuation

[michele]

Why does the following code print "doing other stuff" twice?

def cc
puts "do A"
puts "----> 1. #{caller}"
callcc { |cont| return cont}
puts "----> 2. #{caller}"
puts "do B"
end

puts "calling cc"
cont = cc()
puts "doing other stuff"
cont.call() if cont
puts "end of work"
puts

result:

calling cc
do A
----> 1. remove2.rb:59
doing other stuff
----> 2. remove2.rb:59
do B
doing other stuff
end of work

[steve_d555]

How 'bout something like this:
def cc
puts "do A"
puts "----> 1. #{caller}"
puts "doing other stuff"
callcc { |cont| return cont}
puts "----> 2. #{caller}"
puts "do B"
end

puts "calling cc"
cont = cc()
cont.call() if cont
puts "end of work"
puts

[michele]

The idea was that I wanted to leave cc's work in the middle, to do some work somewhere else and return to cc. Your code will of course work, but it doesn't show my intentions.

[BlackEdder]

It really seems like a bug.. You can see that the line codes are the same in both calls, ----> 2. remove2.rb:59
so clearly the "program" thinks it's being called from that line and returns there, resulting in the code in the middle being execute4d twice. Strangely the code works normally in irb

[michele]

That's because it remembers the context from where it returned - i.e. from callcc { |cont| return cont} in cc()

[BlackEdder]

Oops I kinda read over that line apparently.. What happens is this (let's see if I can explain it in words:)

cc is called from the line cont=cc()... It puts in a call_sign with the callcc and then immediately returns to the "main" program. Then: puts "doing other stuff". Then returns to the call sign, and as you remember cc() was called from the cont=cc() line so as soon as it ends the method cc() it will return to that line and redo: puts "doing other stuff"..

[michele]

http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/36708767909d56fa/6f42acf8c0a259d3#6f42acf8c0a259d3

You can follow this thread at Google Groups. I has some good answers.