As part of making tuples first-class citizens, expliciting the arity upon
function application was needed (so that a function of two args can
transparently -- in the surface language -- be applied to either two arguments
or a pair).
It was decided to actually explicit the whole type of arguments because the cost
is the same, and this is consistent with lambda definitions.
A related change done here is the replacement of the `EOp` node for operators by
an "operator application" `EAppOp` node, enforcing a pervasive invariant that
operators are always directly applied. This makes matches terser, and highlights
the fact that the treatment of operator application is almost always different
from function application in practice.
Added a new type safety invariant to ensure that the type `TDefault` can only appear in certain positions,
* On the left-hand side of an arrow with arity 1, as the type of a scope (for scope calls).
* At the root of the type tree (outside a default).
* On the right-hand side of the arrow at the root of the type (occurs for rentrant variables).
This is crucial to maintain the safety of the type system, as demonstrated in the formal development.
The invariant was checked on all tests cases and on family and housing benefits.
Adjusted inversion invariant about app to handle external objects as well.
The module is renamed to `Mark`, and functions renamed to avoid redundancy:
`Marked.mark` is now `Mark.add`
`Marked.unmark` is now `Mark.remove`
`Marked.map_under_mark` is now simply `Mark.map`
etc.
`Marked.same_mark_as` is replaced by `Mark.copy`, but with the arguments
swapped (which seemed more convenient throughout)
Since a type `Mark.t` would indicate a mark, and to avoid confusion, the type
`Marked.t` is renamed to `Mark.ed` as a shorthand for `Mark.marked` ; this part
can easily be removed if that's too much quirkiness.
- Fix the printer for scopes
- Improve the printer for struct types
- Remove `Print.expr'`. Use `Expr.format` as the function with simplified arguments instead.
- `Print.expr` no longer needs the context
- This removes the need for `expr ~debug` + `expr_debug` ;
use `Print.expr` for normal (non-debug) output,
and `Print.expr' ?debug ()` for possibly debug output.
- This improves consistency of debug expr output in many places
- Prints simplified operators (without type suffix) in non-verbose mode
(this patch also fixes some cases of `Expr.skip_wrappers` and leverages the
binder equality provided by Bindlib)
