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Contents
h1. An Example
This comes from the "Advanced Ruby Course":http://pragmaticstudio.com/ruby/
h1. Continuation
<div style="width: 50%; float: right">
:code code/control/basic_continuation.rb[class=code-normal]
</div>
<div style="width: 50%">
* Construct using @callcc@
** pass it a block
** block receives @Continuation@ object
** invoke that object's @call@ method, and control passes to the end of that block
</div>
h1. Continuations Are Closures
:code code/control/closure_continuation.rb
h1. But...
:code code/control/closure_continuation_2.rb
h1. But...
<div>
:code code/control/closure_continuation_2.rb
<div style="position: relative; left: 60%; top: -3em; font-size: 400%; color: #6b6">Why?</div>
</div>
h1. Implementing throw...catch
Let's try to implement throw and catch so that the following works as expected:
:code code/control/cc_throw_catch.rb[body]
h1. Implementing throw...catch
* We need a thread-local stack of all current catch blocks
* When we see a @catch@, we store the symbol and a continuation for the block on the stack. If that continuation gets called, execution resumes after the block (which is what @catch@ does)
* When we see a @throw@ we traverse it looking for the entry
with the corresponding system.
* When we find that entry, we call the corresponding continuation
bq{font-size="50%"}. This implementation is based on code from Jim Weirich
h1. Catch and Throw
:code code/control/cc_throw_catch.rb[CC class=code-tiny]
h1. And the stack
:code code/control/cc_throw_catch.rb[stack class=code-tiny]
h1. Continuations.
* Can't invoke across threads
* Can carry stale state around with them
* Can use up a lot of memory
* Are not fun to debug
But...
* They'll impress your friends
Version data entries
7 entries across 7 versions & 5 rubygems