On Thursday, March 21, 2019 at 9:30:40 AM UTC-4, Brandon Barker wrote: > > Hi Artyom, > > I'm also grappling with the issue of RT in this case as I'd so far only > thought about it in terms of function calls, but what you and Vanessa say > helped me to understand the issue. Though I haven't managed to get ATS to > have the same behavior as OCaml in the "let expression" above, I suspect it > is possible. The key phrase here seems to be "side-effecting expression", > and relates to the fact that functions in ATS can perform side effects > without having any effect type or IO monad ascribed to the value (again, > iirc). >
Well, maybe that isn't the real key - the real key, I now think, is that ATS doesn't (by default?) model an IO effect. In section 6.9 of http://ats-lang.sourceforge.net/DOCUMENT/INT2PROGINATS/PDF/main.pdf it is mentioned that using both linear and dependent types may be used to do this, though I think the suggestion here is for more than printing to e.g. STDOUT. If anyone has looked at modeling/enforcing an IO-like effect type in ATS, I'd be interested to see it. > > Perhaps tonight I should try out the same in Idris or PureScript, which > are not lazily evaluated by default but do use IO, to get a better > understanding. > > On Thursday, March 21, 2019 at 3:17:46 AM UTC-4, Artyom Shalkhakov wrote: >> >> Hi Brandon, >> >> Admittedly I don't really understand what RT is, but from what I >> understand, in Haskell the expression like [print "ha"] is basically a >> command to the top-level interpreter (which is the language runtime) to >> perform an effect on the console (moreover, it will be evaluated on >> as-needed basis). Moreover, the ";" is itself another comand, the explicit >> sequencing command, the meaning of which is "perform the left-hand side >> effects, then perform the right-hand side effects". Such a command is a >> value, so it can be passed as a value and reused as many times as is >> necessary. In ATS, the expression like [print "ha"] evaluates right there >> to a void/"no value", and the ";" is also NOT a value at all, but rather a >> "shortcut" syntax to a "let-in-end" form. >> >> I like to imagine an interpreter that sits in the Haskell's runtime. >> Values of IO type are commands to this interpreter. Typical Haskell >> IO-based programs are building up these commands as they are being >> evaluated by the runtime. The runtime starts evaluation at the "main" >> expression defined by the programmer. >> >> чт, 21 мар. 2019 г. в 03:45, Brandon Barker <brandon...@gmail.com>: >> >>> I'm a little rusty, so can't come up with many good examples. >>> >>> Apparently it is possible to do something like this in OCaml: >>> >>> implement >>> main0 () = { >>> val () = let >>> val ha = print("ha") >>> in >>> (ha; ha) // How to get two ha's here? >>> end >>> } >>> >>> >>> After running the program, you would only see one "ha", which violates >>> RT. >>> >>> However, ATS doesn't seem to allow a sequence expression in the "in" >>> position of a let expression, as this doesn't compile. Admittedly I'm just >>> trying to see if ATS2 doesn't have RT in this particular case, but it would >>> also be good to know about the sequence expressions here. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "ats-lang-users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to ats-lang-user...@googlegroups.com. >>> To post to this group, send email to ats-lan...@googlegroups.com. >>> Visit this group at https://groups.google.com/group/ats-lang-users. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/ats-lang-users/5eba6b86-4146-4ba2-a87f-f8c511d902f0%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/ats-lang-users/5eba6b86-4146-4ba2-a87f-f8c511d902f0%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> >> >> -- >> Cheers, >> Artyom Shalkhakov >> > -- You received this message because you are subscribed to the Google Groups "ats-lang-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to ats-lang-users+unsubscr...@googlegroups.com. To post to this group, send email to ats-lang-users@googlegroups.com. Visit this group at https://groups.google.com/group/ats-lang-users. To view this discussion on the web visit https://groups.google.com/d/msgid/ats-lang-users/5391973a-4bd4-4238-a007-4dc08d1d9d4d%40googlegroups.com.
