diff options
Diffstat (limited to 'src/Values.ml')
| -rw-r--r-- | src/Values.ml | 217 |
1 files changed, 200 insertions, 17 deletions
diff --git a/src/Values.ml b/src/Values.ml index 969e01d2..58934e03 100644 --- a/src/Values.ml +++ b/src/Values.ml @@ -111,7 +111,7 @@ and adt_value = { and borrow_content = | SharedBorrow of (BorrowId.id[@opaque]) (** A shared value *) | MutBorrow of (BorrowId.id[@opaque]) * typed_value - (** A mutably borrowed value *) + (** A mutably borrowed value. *) | InactivatedMutBorrow of (BorrowId.id[@opaque]) (** An inactivated mut borrow. @@ -127,6 +127,9 @@ and borrow_content = and loan_content = | SharedLoan of (BorrowId.set_t[@opaque]) * typed_value | MutLoan of (BorrowId.id[@opaque]) + (** TODO: we might want to add a set of borrow ids (useful for inactivated + borrows, and extremely useful when giving shared values to abstractions). + *) and typed_value = { value : value; ty : ety } [@@deriving @@ -234,31 +237,123 @@ and adt_avalue = { Note that the children avalues are independent of the parent avalues. For instance, the child avalue contained in an [AMutLoan] will likely - contain other, independent loans. We keep track of the hierarchy because - we need it to properly instantiate the backward functions when generating - the pure translation. + contain other, independent loans. + Keeping track of the hierarchy is not necessary to maintain the borrow graph + (which is the primary role of the abstractions), but it is necessary + to properly instantiate the backward functions when generating the pure + translation. *) and aloan_content = | AMutLoan of (BorrowId.id[@opaque]) * typed_avalue + (** A mutable loan owned by an abstraction. + + Example: + ======== + ``` + fn f<'a>(...) -> &'a mut &'a mut u32; + + let px = f(...); + ``` + + We get (after some symbolic exansion): + ``` + abs0 { + a_mut_loan l0 (a_mut_loan l1) + } + px -> mut_borrow l0 (mut_borrow @s1) + ``` + *) | ASharedLoan of (BorrowId.set_t[@opaque]) * typed_value * typed_avalue + (** A shared loan owned by an abstraction. + + Example: + ======== + ``` + fn f<'a>(...) -> &'a u32; + + let px = f(...); + ``` + + We get: + ``` + abs0 { a_shared_loan {l0} @s0 ⊥ } + px -> shared_loan l0 + ``` + *) | AEndedMutLoan of { given_back : typed_avalue; child : typed_avalue } - (** TODO: in the formalization, given_back was initially a typed value - (not an avalue). It seems more consistent to use a value, especially - because then the invariants about the borrows are simpler (otherwise, - there may be borrow ids duplicated in the context, which is very - annoying). - I think the original idea was that using values would make it - simple to instantiate the backward function (because projecting - deconstructs a bit the values with which we feed the function). - *) + (** An ended mutable loan in an abstraction. + We need it because abstractions must keep track of the values + we gave back to them, so that we can correctly instantiate + backward functions. + + Example: + ======== + ``` + abs0 { a_mut_loan l0 ⊥ } + x -> mut_borrow l0 (U32 3) + ``` + + After ending `l0`: + + ``` + abs0 { a_ended_mut_loan { given_back = U32 3; child = ⊥; } + x -> ⊥ + ``` + + TODO: in the formalization, given_back was initially a typed value + (not an avalue). It seems more consistent to use a value, especially + because then the invariants about the borrows are simpler (otherwise, + there may be borrow ids duplicated in the context, which is very + annoying). + I think the original idea was that using values would make it + simple to instantiate the backward function (because projecting + deconstructs a bit the values with which we feed the function). + *) | AEndedSharedLoan of typed_value * typed_avalue + (** Similar to [AEndedMutLoan] but in this case there are no avalues to + give back. Actually, we could probably forget the shared value + altogether (and just keep the child avalue). + *) | AIgnoredMutLoan of (BorrowId.id[@opaque]) * typed_avalue + (** An ignored mutable loan. + + We need to keep track of ignored mutable loans, because we may have + to apply projections on the values given back to those loans (say + you have a borrow of type `&'a mut &'b mut`, in the abstraction 'b, + the outer loan is ignored, however you need to keep track of it so + that when ending the borrow corresponding to 'a you can correctly + project on the inner value). + + Example: + ======== + ``` + fn f<'a,'b>(...) -> &'a mut &'b mut u32; + let x = f(...); + + > abs'a { a_mut_loan l0 (a_ignored_mut_loan l1 ⊥) } + > abs'b { a_ignored_mut_loan l0 (a_mut_loan l1 ⊥) } + > x -> mut_borrow l0 (mut_borrow l1 @s1) + ``` + *) | AEndedIgnoredMutLoan of { given_back : typed_avalue; child : typed_avalue } + (** Similar to [AEndedMutLoan], for ignored loans *) | AProjSharedLoan of (abstract_shared_borrows[@opaque]) - (** A projected shared loan - TODO: remove? Does it make sense? Maybe - I should rename that to AIgnoredSharedLoan... *) + (** An ignored shared loan. + TODO: rename and change fields to: typed_avalue + + Example: + ======== + ``` + fn f<'a,'b>(...) -> &'a &'b u32; + let x = f(...); + + > abs'a { a_shared_loan {l0} (shared_borrow l1) (a_ignored_shared_loan ⊥) } + > abs'b { a_ignored_shared_loan (a_shared_loan {l1} @s1 ⊥) } + > x -> shared_borrow l0 + ``` + *) -(** Note that when a borrow content is ended, it is replaced by Bottom (while +(** Note that when a borrow content is ended, it is replaced by ⊥ (while we need to track ended loans more precisely, especially because of their children values). @@ -272,10 +367,98 @@ and aloan_content = *) and aborrow_content = | AMutBorrow of (BorrowId.id[@opaque]) * typed_avalue + (** A mutable borrow owned by an abstraction. + + Is used when an abstraction "consumes" borrows, when giving borrows + as arguments to a function. + + Example: + ======== + ``` + fn f<'a>(px : &'a mut u32); + + > x -> mut_loan l0 + > px -> mut_borrow l0 (U32 0) + + f(move px); + + > x -> mut_loan l0 + > px -> ⊥ + > abs0 { a_mut_borrow l0 (U32 0) } + ``` + *) | ASharedBorrow of (BorrowId.id[@opaque]) + (** A shared borrow owned by an abstraction. + + Example: + ======== + ``` + fn f<'a>(px : &'a u32); + + > x -> shared_loan {l0} (U32 0) + > px -> shared_borrow l0 + + f(move px); + + > x -> shared_loan {l0} (U32 0) + > px -> ⊥ + > abs0 { a_shared_bororw l0 } + ``` + *) | AIgnoredMutBorrow of typed_avalue + (** An ignored mutable borrow. + + This is mostly useful for typing concerns: when a borrow doesn't + belong to an abstraction, it would be weird to ignore it altogether. + + Example: + ======== + ``` + fn f<'a,'b>(ppx : &'a mut &'b mut u32); + + > x -> mut_loan l0 + > px -> mut_loan l1 + > ppx -> mut_borrow l1 (mut_borrow l0 (U32 0)) + + f(move ppx); + + > x -> mut_loan l0 + > px -> mut_loan l1 + > ppx -> ⊥ + > abs'a { a_mut_borrow l1 ⊥ } // TODO: there might be an a_ignored_mut_borrow in the inner value + > abs'b { a_ignored_mut_borrow (a_mut_borrow l0 (U32 0)) } + ``` + *) | AProjSharedBorrow of (abstract_shared_borrows[@opaque]) - (** A projected shared borrow *) + (** A projected shared borrow. + + When giving shared borrows as arguments to function calls, we + introduce new borrows to keep track of the fact that the function + might reborrow values inside. + + Example: + ======== + Below, when calling `f`, we need to introduce one shared borrow per + borrow in the argument. + ``` + fn f<'a,'b>(pppx : &'a &'b &'c mut u32); + + > x -> mut_loan l0 + > px -> shared_loan {l1} (mut_borrow l0 (U32 0)) + > ppx -> shared_loan {l2} (shared_borrow l1) + > pppx -> shared_borrow l2 + + f(move pppx); + + > x -> mut_loan l0 + > px -> shared_loan {l1, l3, l4} (mut_borrow l0 (U32 0)) + > ppx -> shared_loan {l2} (shared_borrow l1) + > pppx -> ⊥ + > abs'a { a_proj_shared_borrow {l2} } + > abs'b { a_proj_shared_borrow {l3} } // l3 reborrows l1 + > abs'c { a_proj_shared_borrow {l4} } // l4 reborrows l0 + ``` + *) (* TODO: we may want to merge this with typed_value - would prevent some issues when accessing fields... *) |