If a lambda set is non-recursive, but contains naked recursion pointers,
we should not fill those naked pointers in with the slot of the lambda
set during interning. Such naked pointers must belong to an encompassing
lambda set that is in fact recursive, and will be filled in later.
For example, `LambdaSet([Foo, LambdaSet(Bar, [<rec>])] as <rec>)` should
not have the inner lambda set's capture be filled in with itself.
Also, during reification of recursion pointers, we do not need to
traverse re-inserted lambda sets again, since they were just fixed-up.
Closes#5026
This change also means we must update the interface of `Dict.empty` and
`Set.empty` from
```
Dict.empty : Dict k v
```
to
```
Dict.empty : {} -> Dict k v
```
The nullable ID always has zero tags. For everything else, we should
just match with the arity of the number of arguments, which doesn't
include the tag ID.
Previously, if the lambda set passed to a HOLL contained any function
that captured, we would assume that the specialization of the HOLL we
should make for each function in the lambda set that we dispatch to
should capture.
This is not right. Instead, we should specialize for each lambda in the
set passed to the HOLL. The present patch enforces that, making sure
that for each lambda in the set, we compute the exact proc layout needed
to call the lambda, based on the captures of the specific lambda in the
set, rather than looking at the set entirely.
Some of the head-constructor tests we generate can be supersets of other tests.
Edges must be ordered so that more general tests always happen after their
specialized variants.
For example, patterns
[1, ..] -> ...
[2, 1, ..] -> ...
may generate the edges
ListLen(>=1) -> <rest>
ListLen(>=2) -> <rest>
but evaluated in exactly this order, the second edge is never reachable.
The necessary ordering is
ListLen(>=2) -> <rest>
ListLen(>=1) -> <rest>
Closes#4732
When compiling a pattern match like
```
[] -> ..
[_] -> ..
[_, ..] -> ..
```
to a decision tree, we must make sure that the last test (len >= 1)
does not touch the branch reached by the second test (len == 1). It is
enough to ban (len >=) tests from ever touching exact-sized list
patterns, because a spread test (len >=) can never reach an exact-sized
test.
On the other hand, an exact-sized test can reach a spread pattern,
because in
```
[_, _] -> ..
[..] -> ..
```
the last branch generates tests for patterns `[]` and `[_]`, and we would
like those patterns to be covered by the spread test (len >= 0)!
Closes#4685
