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[Caml-list] kprintf with user formatters
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Date: | 2004-07-16 (17:44) |
From: | Markus Mottl <markus@o...> |
Subject: | Re: [Caml-list] kprintf with user formatters |
On Fri, 16 Jul 2004, Pierre Weis wrote: > Hmm, this sounds extremely lazy to me; so this suggests thunk > programming; hey, we have that in the language, so let's go! > > let log level thunk = > if may_log level then thunk ();; > > ... > > log 2 (fun () -> > eprintf "Argument 1 is hard to compute %d\n" (ackermann x x)) I have used thunks (and lazy values) before, but they are usually syntactically ugly. Instead of: log (fun () -> sprintf "%d" n) I'd rather want to write log "%d" n without having the log function compute a string from an integer if this is not necessary. Would this really be so difficult to support? > That's the way we use to log in the OcamlP3l compiler: we've got no > runtime penalty if there is no necessity to log. Well, you have to create a thunk, but this cost is acceptable to me. I just don't want to clutter my code with thunks + additional sprintf statements. > Moreover, this solution is general enough to accomodate threads, > side effects, or whatever. You always need mutexes if you want to prevent that your output gets messed up by multiple threads. > To me the (fun () -> ) additional verbosity is not so bad: it clearly > emphasizes that nothing at all is evaluated when logging is unnecessary. It's rather the other way round: people using format strings may get the wrong idea that arguments are not converted if there is no output. > To go beyond that, we would need some help from the language that > would offer some provision for debugging from a special debug keyword, > semantically reminiscent to lazy and assert (as a kind of combined > semantics of both constructs). A compiler flag would then > automatically remove the debugging code (as is done for assert with > the -noassert flag) and the compiler will automatically insert the > (fun () -> ) as it already does in the case of lazy ... I don't think it is necessary or even useful to introduce new keywords. A customized, beautiful solution would be possible with camlp4, thunks solve the problem semantically, but look ugly, and some support for a kind of zprintf would be ideal :-) Regards, Markus -- Markus Mottl http://www.oefai.at/~markus markus@oefai.at ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners