Hi Thomas, The hack works as intended. But it has also made me cautious about the compiler behaviour. Just because the code works in repl, there is no guarantee it will work in a compiled state. That means more tests for me.
Thank you for the hack and the explanation provided. - Joe On Sun, Dec 7, 2014 at 9:16 AM, Thomas Chust <[email protected]> wrote: > On Sat, 6 Dec 2014, Joe Python wrote: > > I was experimenting with a coroutine example which i got from the c2 >> website. see link below for code. >> >> http://paste.call-cc.org/paste?id=cf4489b9de4820b330dc34371ea3b7 >> 3a18115a4b#a0 >> >> I get the expected output when I run the code using csi >> [...] >> However when i run the executable which i compiled with csc, i get [...] >> unexpected output. >> [...] >> > > Hello Joe, > > this seems to have something to do with the fact that the toplevel behaves > slightly differently in compiled and interpreted code. While the toplevel > expressions of each compilation unit essentially form a single procedure > body, the toplevel expressions fed to the interpreter are processed > independently. This can make a difference when capturing the continuation > of a toplevel expression. > > Furthermore, the control flow in your code is probably not what you expect > it and want it to be: Your coroutine constructor arranges for the > continuation of the *first* coroutine invocation to be captured and used > for returns of *every* yield statement. > > You can easily verify the combined effect of these phenomena by inserting > some print statements around the coroutine invocations at the end of your > program. In the interpreted case, the captured continuation incidentally > returns control to the surrounding read eval loop, however in the compiled > case the captured continuation returns you to the place in the program > between the first an second explicit coroutine invocation, effectively > constructing an endless loop around the second invocation. > > A quick fix for the problem would be to actually use the new return > continuations returned by the yield expressions upon re-entry into the > coroutine: Simply replace every call of (yield WHATEVER) in your coroutine > body by (set! yield (yield WHATEVER)) and the program will behave > identically (and correctly, I might add) in compiled and interpreted mode. > > If you find that solution inelegant, you might want to encapsulate this > behaviour of yield into a macro or use parameters to implement a global > yield procedure instead. > > I hope this helps :-) > > Ciao, > Thomas > > > -- > When C++ is your hammer, every problem looks like your thumb. > >
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