On Fri, Jan 22, 2021 at 09:47:24AM -0500, jbranso--- via Bug reports for GUILE, GNU's Ubiquitous Extension Language wrote: > Ricardo Wurmus <rek...@elephly.net> writes: > > > Hi Joshua, > > > >> When I look at > >> > >> #+BEGIN_SRC scheme > >> (define (thunk) > >> (lambda (x) > >> x)) > >> #+END_SRC > > > > […] > > > >> My thought is, this is clearly a mistake. This person needs to change > >> the above code. > > > > How is this clearly a mistake? The definition of “thunk” above is > > perfectly fine and also common. > > Thanks again for responding. I'm still learning scheme, and it's cool > that this email chain has helped clarify some things. :) > > Ahh. I see now that the proper way to call thunk is to do this: > ((thunk) "the") > $1 = "the" > > I had assumed that every time one called thunk, it would result in a > runtime error. I did not realize that there was a way to properly call > thunk. Wow. Scheme is truly impressive. > > Interestingly, I had wrongly assumed that > > #+BEGIN_SRC scheme > (thunk "test\n") ;; I assumed program execution would stop here > (display "Hello World\n") > #+END_SRC > > program execution would stop at (thunk "test\n"). But it actually > caries on with execution of the program:
What happens is an "exception". It can be handled (then it's up to the exception handler to end the program or do something else). > #+BEGIN_SRC scheme > <stdin>:5:0: warning: possibly wrong number of arguments to `thunk' > ice-9/boot-9.scm:1669:16: In procedure raise-exception: > Wrong number of arguments to #<procedure thunk ()> > > Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. > Hello World > #+END_SRC This is the REPL's exception handler talking to you. It's there to help you debug the problem. Were it a standalone program, it would have terminated right away. (note that I'm not the most appropriate person to explain such things, I can barely wrap my head around them :-) Cheers [1] https://www.gnu.org/software/guile/docs/master/guile.html/Exceptions.html - tomás
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