4 ms·

> It would be desirable for our programs to always have meanings that aligned with their behaviour, but we shouldn't turn a blind eye to the fact that many prog

> It would be desirable for our programs to always have meanings that aligned with their behaviour, but we shouldn't turn a blind eye to the fact that many programs don't. The meaning of a program is its behavior, period. If reality doesn't agree with your views, it's your fault, not reality's. > Any practical programming language will give you some way to find the memory address of a particular value, so values that we usually consider as semantically identical are not actually indistinguishable in practice. Standard ML doesn't give you any way to get the memory address of a particular value, so values that are semantically identical are actually indistinguishable in practice. > We deal with this by only assigning semantics to a subset of the language that excludes those operations. That doesn't make sense. Semantics is a property of the real programming language you are using, not the fictitious one you wish you were using.

lmm 9y ago
> The meaning of a program is its behavior, period. If reality doesn't agree with your views, it's your fault, not reality's. That's not the usual meaning of, well, meaning. > Standard ML doesn't give you any way to get the memory address of a particular value, so values that are semantically identical are actually indistinguishable in practice. Just tried it to be sure: fun address i = Unsafe.cast(ref i) : Int32.int ;; val a = 4 :: nil ;; val b = 4 :: nil ;; address (a) ;; address (b) ;; address (a) ;; And yep, a and b are semantically identical values but distinguishable in practice: val address = fn : 'a -> Int32.int val a = [4] : int list val b = [4] : int list val it = ~175003712 : Int32.int val it = ~174998232 : Int32.int val it = ~175003712 : Int32.int
- catnaroek 9y ago
  SML/NJ is not an implementation of Standard ML. It's known to be non-conformant in several ways: http://mlton.org/SMLNJDeviations http://mlton.org/SMLNJDeviations
  - lmm 9y ago
    If SML/NJ doesn't count as Standard ML then I'd say Standard ML doesn't count as a practical programming language.
    - catnaroek 9y ago
      I use MLton and Poly/ML on a daily basis. No problems with them at all.

lmm 9y ago

> The meaning of a program is its behavior, period. If reality doesn't agree with your views, it's your fault, not reality's. That's not the usual meaning of, well, meaning. > Standard ML doesn't give you any way to get the memory address of a particular value, so values that are semantically identical are actually indistinguishable in practice. Just tried it to be sure: fun address i = Unsafe.cast(ref i) : Int32.int ;; val a = 4 :: nil ;; val b = 4 :: nil ;; address (a) ;; address (b) ;; address (a) ;; And yep, a and b are semantically identical values but distinguishable in practice: val address = fn : 'a -> Int32.int val a = [4] : int list val b = [4] : int list val it = ~175003712 : Int32.int val it = ~174998232 : Int32.int val it = ~175003712 : Int32.int

catnaroek 9y ago
SML/NJ is not an implementation of Standard ML. It's known to be non-conformant in several ways: http://mlton.org/SMLNJDeviations http://mlton.org/SMLNJDeviations
- lmm 9y ago
  If SML/NJ doesn't count as Standard ML then I'd say Standard ML doesn't count as a practical programming language.
  - catnaroek 9y ago
    I use MLton and Poly/ML on a daily basis. No problems with them at all.