If the rule for bindings of the form:
(define a b:(mutable x))
is that a receives a copy of b -- mutability shallowly lost due to copy,
Consider:
(define a (mutable 10))
The type of a is int and NOT (mutable int) , mutability shallowly lost
due to copy.
The mutable value constructor is actually never useful (It did make the
10 mutable, but the effect never survives). So I think we should
probably remove it from the language.
One can always write:
(define a:(mutable 'a) (mutable 10))
or even
(define a:(mutable 'a) 10)
This is actually good because mutability concerns the cell containing
'a' and not the value that is contained there, and the mutable
qualification is better expressed along with a.
Also, if I have a variant:
(defunion (list 'a) (Nil) (Cons (mutable 'a)))
(define alist (list int))
The mutable qualifier in the argument of Cons is useless because, alist
is itself not mutable, and there is no way in the language (and rightly
so) to name the argument of Cons and independently mutate it.
[Just for reference: In Ocaml, the mutable qualifier can syntactically
only appear on field names of records]
Swaroop.
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