8 ms·

Personally, I'd argue there's only one concept -- pass-by-value -- with a whole lot of language-specific syntactic sugar as to what is getting passed by value.

Personally, I'd argue there's only one concept -- pass-by-value -- with a whole lot of language-specific syntactic sugar as to what is getting passed by value. But I'll call myself out on that being even more pedantic than the current discussion.

seanmcdirmid 8y ago
That sounds like Robert Harper’s argument that all languages are statically typed, it’s just that some languages only have one type.
- twic 8y ago
  I've heard this term "unityped", but i'd always written it off as a politically correct way of saying "untyped". Is there actually a worthwhile argument for it? Having thought about it for a minute or two, it seems pretty silly to me . Types are all about restricting the set of values an expression can have, and restricting the set of operations you can perform on an expression, such that any operation you're allowed to perform on a value will always do something sensible. Untyped languages don't do that, which makes them quite different from typed languages. But then i've only thought about it for a minute or two. I could imagine a genuinely unityped language. Perhaps one where every value is a vector of real numbers with an infinite number of zeroes on the end, and the operations are piecewise arithmetic, dot products, interleaving, appending, etc. That would behave quite differently to the languages where you get "undefined is not a function" and friends.
  - qznc 8y ago
    Untyped languages actually allow you to perform any operation on any value and will always do something sensible. The sensible thing to do is to throw an exception in most cases.
    - seanmcdirmid 8y ago
      The difference between safe dynamically typed and untyped is whether the throw will happen or not. There are degrees of safety even in dynamically typed languages.
      - coldtea 8y ago
        Where by "safe dynamically type" you probably mean "strongly typed" (as eg Python).
  - clhodapp 8y ago
    I think the argument is that when every value inhabits the sole type and everything accepts that type, you get a system that works the way "untyped" languages do. Why have two separate concepts when you can gain some true conclusions by unifying? I think Harper would take issue with it being explained this way, but one can think of Ruby and Python being languages where everything is a pointer to a HashMap and everything else is just sugar on top of that (similar to the above argument about Java and the sugar with the pointers). I don't think Harper would like that way of explaining it because it's over-focused on an example instead of sticking to the concept and because it conflates (statically-knowable) types with (runtime) classes, which is big no-no with him.
  - edflsafoiewq 8y ago
    To a first approximation, a type is an equivalence class of expressions such that the set of valid programs is closed under substitution of one of these expressions for any other (compare with the definition of a part of speech in grammar). In a typical dynamic language, anywhere the syntax requires an expression, any expression will do, so there is only one equivalence class. This is in contrast to, say, Java, where (2/3) can be part of a valid program, but ("abc"/3) cannot, so 2 and "abc" cannot belong to the same equivalence class.
  - coldtea 8y ago
    >I've heard this term "unityped", but i'd always written it off as a politically correct way of saying "untyped". Is there actually a worthwhile argument for it? Yes. Python e.g. is more unityped (union typed, things have a type, but are handled as a union among several options) than untyped. tcl, on the other hand, is more untyped (everything is the same thing: string-like).
- mannykannot 8y ago
  They might be similar in shifting the focus from terminology to semantics.
abritinthebay 8y ago
Though you’re strictly correct. Honestly it’s a terminology problem. The whole “pass by x” really confuses things. It’s really more “represented by foo” underlying the passing that is important.

seanmcdirmid 8y ago

That sounds like Robert Harper’s argument that all languages are statically typed, it’s just that some languages only have one type.

twic 8y ago
I've heard this term "unityped", but i'd always written it off as a politically correct way of saying "untyped". Is there actually a worthwhile argument for it? Having thought about it for a minute or two, it seems pretty silly to me . Types are all about restricting the set of values an expression can have, and restricting the set of operations you can perform on an expression, such that any operation you're allowed to perform on a value will always do something sensible. Untyped languages don't do that, which makes them quite different from typed languages. But then i've only thought about it for a minute or two. I could imagine a genuinely unityped language. Perhaps one where every value is a vector of real numbers with an infinite number of zeroes on the end, and the operations are piecewise arithmetic, dot products, interleaving, appending, etc. That would behave quite differently to the languages where you get "undefined is not a function" and friends.
- qznc 8y ago
  Untyped languages actually allow you to perform any operation on any value and will always do something sensible. The sensible thing to do is to throw an exception in most cases.
  - seanmcdirmid 8y ago
    The difference between safe dynamically typed and untyped is whether the throw will happen or not. There are degrees of safety even in dynamically typed languages.
    - coldtea 8y ago
      Where by "safe dynamically type" you probably mean "strongly typed" (as eg Python).
- clhodapp 8y ago
  I think the argument is that when every value inhabits the sole type and everything accepts that type, you get a system that works the way "untyped" languages do. Why have two separate concepts when you can gain some true conclusions by unifying? I think Harper would take issue with it being explained this way, but one can think of Ruby and Python being languages where everything is a pointer to a HashMap and everything else is just sugar on top of that (similar to the above argument about Java and the sugar with the pointers). I don't think Harper would like that way of explaining it because it's over-focused on an example instead of sticking to the concept and because it conflates (statically-knowable) types with (runtime) classes, which is big no-no with him.
- edflsafoiewq 8y ago
  To a first approximation, a type is an equivalence class of expressions such that the set of valid programs is closed under substitution of one of these expressions for any other (compare with the definition of a part of speech in grammar). In a typical dynamic language, anywhere the syntax requires an expression, any expression will do, so there is only one equivalence class. This is in contrast to, say, Java, where (2/3) can be part of a valid program, but ("abc"/3) cannot, so 2 and "abc" cannot belong to the same equivalence class.
- coldtea 8y ago
  >I've heard this term "unityped", but i'd always written it off as a politically correct way of saying "untyped". Is there actually a worthwhile argument for it? Yes. Python e.g. is more unityped (union typed, things have a type, but are handled as a union among several options) than untyped. tcl, on the other hand, is more untyped (everything is the same thing: string-like).
mannykannot 8y ago
They might be similar in shifting the focus from terminology to semantics.

abritinthebay 8y ago

Though you’re strictly correct. Honestly it’s a terminology problem. The whole “pass by x” really confuses things. It’s really more “represented by foo” underlying the passing that is important.