Designing programming languages is hard. I think every nontrivial programming language has at least a few "semantic messes"; even Scheme (R6RS) has a long specification with edge-cases (ex: https://www.r6rs.org/final/html/r6rs/r6rs-Z-H-6.html#node_se...). Meanwhile, C++ is a semantic mess that contains at least a few programming languages.
> Yet an expression such as cols (replicate 0 (replicate 3 0)) should still work (and evaluate to 3)
Denotational or operational semantics: pick one for your programming language and stick to it. The author (who I generally think is very smart) here is striving for denotational semantics (type level data) and trying to torture the operations into supplying the appropriate result. Operationally `cols (replicate 0 (replicate 3 0))` is 0 not 3. So now you have to bend over backwards and implement custom shape functions that not only return weird answers but have to be special cased AND context sensitive - ie without trying the language I'm 100% sure that
cols (replicate 0 "x")
returns zero, but as described here
cols (replicate 0 (replicate k "x"))
returns k. Ie cols has to introspect semantically into its argument. That's not just tedious, it's impossible unless you don't let people add names that can participate (ie arbitrary functions). Or you ask them to implement the same shape functions (which doesn't solve the problem because they'll be no more equipped than you are).
> if I had more experience implementing dependently typed languages, then perhaps I would not find it so weird, as it really just makes type constructors similar to functions, which they would be in a fully dependently typed language.
Yeah. I was screaming for most of this piece, because this all seems like standard dependently-typed stuff, and ironically enough implementing full dependent types would probably end up being easier than trying to handle this one feature as a special case.
This is a poorly named language IMO, since Futhark is the name of Norse runes (which is what I thought this was about). Why do so many programming languages have to be named things that are hard to search for?
armchairhacker|5 months ago
pjmlp|5 months ago
C++ has a couzy group of friends among mainstream languages, that share similar age.
almostgotcaught|5 months ago
Denotational or operational semantics: pick one for your programming language and stick to it. The author (who I generally think is very smart) here is striving for denotational semantics (type level data) and trying to torture the operations into supplying the appropriate result. Operationally `cols (replicate 0 (replicate 3 0))` is 0 not 3. So now you have to bend over backwards and implement custom shape functions that not only return weird answers but have to be special cased AND context sensitive - ie without trying the language I'm 100% sure that
returns zero, but as described here returns k. Ie cols has to introspect semantically into its argument. That's not just tedious, it's impossible unless you don't let people add names that can participate (ie arbitrary functions). Or you ask them to implement the same shape functions (which doesn't solve the problem because they'll be no more equipped than you are).sestep|5 months ago
lmm|5 months ago
Yeah. I was screaming for most of this piece, because this all seems like standard dependently-typed stuff, and ironically enough implementing full dependent types would probably end up being easier than trying to handle this one feature as a special case.
Ferret7446|4 months ago
milesrout|5 months ago
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