Hi, On +2022-07-27 14:31:32 -0400, Maxim Cournoyer wrote: > Hi, > > Tobias Geerinckx-Rice <m...@tobias.gr> writes: > > > Hi Maxim, > > > > Maxim Cournoyer 写道： > >> I'd suggest we revisit 8cb1a49a3998c39f315a4199b7d4a121a6d66449 to > >> use > >> 'unspecified (the symbol) instead of *unspecified*, which *can* be > >> serialized without any fuss in gexps. > > > > Bah. Could we provide our own reader? > > > > I'd much rather this be addressed in Guile (or failing that, > > transparently by Guix) than have to deal with some magical > > symbol. IIRC that was the argument for using *unspecified* in the > > first place, and I think it makes sense. > > > > This looks more like an unexplored oversight than a well-reasoned > > restriction to me. > > This was my original impression, but thinking more about it, it became > apparent that *unspecified* is well, unspecified and shouldn't be relied > on by people to be something well defined. For some background reading, > see [0]. So it seems wrong in Scheme to actively set things to > *unspecified*, and give a specific meaning to that. > > I think the semantic of the language is that it is to be used as the > lack of a return value from a procedure or syntax, e.g.: > > (unspecified? (if #f 'one-arm-if)) -> #t > > Having 'unspecified?' even defined in Guile seems to go against that > idea; perhaps because Wingo themselves seems to disagree in [0]. > > I'm also thinking 'unspecified being too close to *unspecified* is > probably going to cause confusion down the line. Reverting to the > originally used 'disabled may be the lesser evil. > > Other thoughts? > > Thanks, > > Maxim > > [0] > https://scheme-reports.scheme-reports.narkive.com/QSQtJSAh/unspecified-values > > >
Lots of systems are dealing with this issue, it seems, judging from [1] https://en.wikipedia.org/wiki/Bottom_type I think the problem is you really need a tuple to return both data and metadata unambiguously from anything that produces a result (or not, which is a result). Something like read-delimited with the 'split option, or using catch. Personally, if I were designing a language :), my goal would be to have nothing unspecified, and no undefined behaviour outside of physical failures ;-) *unspecified* seems me like an ok word for the unasserted/high-impedance state of tri-state memory address bus electronic logic, but IMO the example above --8<---------------cut here---------------start------------->8--- > (unspecified? (if #f 'one-arm-if)) -> #t --8<---------------cut here---------------end--------------->8--- is not nice. (A nit, but For one thing "specified?" ought to be the question IMO, if you are ging to have that concept, not "unspecified?" :) What about using characters from some private upper unicode section to represent various kinds of unspecified things? E.g., as guile named chars, #\unspecified_function_retval #\unspecified_function_error #\unspecified_macro_err #\unspecified_exception #\nil or #\not_an_object -- or #\nao -- can't use #\n :) #\paradox -- e.g., (eval-nl-string "this sentence is lying") #\nonsense -- e.g. when a question is based on false premises (eval-nl-string "Bob is bareheaded: Bob, is your hat too tight?") Hm, one could argue that (+ "ab" "cd") could be based on the false premise that + was overloaded like --8<---------------cut here---------------start------------->8--- scheme@(guile-user) [1]> (let*( (+ string-append) (sum (+ "ab" "cd"))) sum) $8 = "abcd" --8<---------------cut here---------------end--------------->8--- and if it wasn't, should return #\nonsense :) (though maybe as part of the exception, which is practical for debugging etc :) #\ #\guix_bottom -- a private unicode rather than U+22A5 which could be returned as a valid character value by some functon. --8<---------------cut here---------------start------------->8--- $ echo -en "\u22a5"|unicode-info "⊥": glyph codepoint .....int name... _⊥_ +U0022a5 8869 UP TACK --8<---------------cut here---------------end--------------->8--- Well, hope you can extract something useful from the above :) BTW, I didn't get far via the link [0] :( --8<---------------cut here---------------start------------->8--- 🤖 Hungry for data? 🤖 As you guessed, this page is to confirm your affiliation to the human race. about - legalese Loading... --8<---------------cut here---------------end--------------->8--- Ok machine, you identified me as human, and kept me out. Happy? No, I know, machines can only fake that. -- Regards, Bengt Richter
