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.
rather than scattered in structures
The context is still hierarchical for defs though, so one needs to retrieve the
path to lookup in the correct context for info. Exceptions are enums and struct
defs, which are re-exposed at toplevel.
... and add a custom printer
Since this is a very common bug, this patch should gain us a lot of time when
debugging uncaught Not_found errors, because the element not found can now be
printed straight away without the need for further debugging.
The small cost is that one should remember to catch the correct specialised
`Foo.Map.Not_found _` exception rather than the standard `Not_found` (which
would type-check but not catch the exception). Using `find_opt` should be
preferred anyway.
Note that the other functions from the module `Map` that raise `Not_found` are
not affected ; these functions are `choose`, `min/max_binding`,
`find_first/last` which either take a predicate or fail on the empty map, so it
wouldn't make sense for them (and we probably don't use them much).
