Looks like some details were hidden in the publications that even the most proficient users feel ambiguous.
In section 7.7 of the definitive article:
Scala's type system unifies ML modules, object-oriented, and functional
programming. The Dependent Object Types (DOT) family of calculi has been
proposed as a new foundation for Scala and similar languages. Unfortunately, it
is not clear how DOT...
I found the following deduction:
“As the final step, we unify the separate constructs for recursion,
records, and lambda abstractions, into a single notion of object.”
I wonder if this exception is caused by such lossy merging of concepts, should this rule be explicitly defined or even generalised?
May 9, 2023, 3:52pm
I have no idea what you are talking about. Section 7.7 of what? Do you have a specific question to ask?
Just added the publication that contains section 7.7.
Sorry I just realised that DOT has several seminal publications. Hope it is clear now
May 9, 2023, 10:06pm
I don’t know about DOT, but in the Scala type system,
this.type is the target of the fundamental “as seen from” meta operation on types :
For a Scala 3 equivalent, I happened to open today a PR to update that section of the spec to Scala 3, which is already quite a bit closer to DOT:
04:09PM - 09 May 23 UTC
There are two fundamental differences between the type sytems of Scala 2 and 3,
… which made a fundamental rewrite desirable:
- Scala 2 defines path-dependent types in terms of type projections, whereas Scala 3 is path-dependent first, and has not general type projects.
- Scala 2 has ad hod higher-kinded type parameters and polymorphic type aliases, whereas Scala 3 has first-class type lambdas and is fundamentally higher order.
We therefore rewrite the entire type system section of the spec to be higher-kinded and path-dependent first. In the process, we also revise refined types to better fit the path-dependent nature.
I (sjrd) took the liberty to add myself as a contributor in the index page of the spec, as I believe this constitutes a fundamental contribution to the language specification.
The rendered version of the Types chapter can be seen here:
[Types Scala 3.pdf](https://github.com/lampepfl/dotty/files/11433246/Types.Scala.3.pdf)
this is just an identifier bound when we create a record. So,
this.T is a path dependent type, for any member type
T. But DOT does not have singleton types. So
this.type is not handled. It would be interesting to see an extension of DOT along these lines.
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