*Disclaimer*: This is intended for discussion
My impression is that the with-exceptions backend is to be superseded by the
without-exception backend, which is more general and more efficient. Therefore,
seeing the added complexity of maintaining the two in parallel, I see no good
reason to keep the with-exceptions version now that the equivalence of their
semantics have been proved.
It will also be nice to reduce divergences between the different backends ; and
this should make further simplifications possible (e.g. some thunkings may no
longer be needed)
Of course I am ready to hear arguments in favor of keeping it, be it in the mid-
or long-term.
This patch removes the `--avoid-exceptions` flag, making it the only option, and
the corresponding `with_exceptions` variant of the dcalc->lcalc translation. It
doesn't do further simplifications.
Support for manipulating toplevel functions as values was buggy, because the
recursion after eta-expansion would fall into the pattern for a `let..in` and
not do the expected transformation.
The patch explicitely builds the closure in that case, avoiding such issues with
recursion.
mostly reverting to the ones the interpreter was printing ; for the case of
divisions, we choose to point to the denominator instead of the operator as it's
where the only possible error (division by zero) comes from.
Positions within the Default terms are specially important since they can come
from separate definitions in the source (before this, we would be falling back
to the single declaration).
- Clearly distinguish Exceptions from Errors. The only catchable exception
available in our AST is `EmptyError`, so the corresponding nodes are made less
generic, and a node `FatalError` is added
- Runtime errors are defined as a specific type in the OCaml runtime, with a
carrier exception and printing functions. These are used throughout, and
consistently by the interpreter. They always carry a position, that can be
converted to be printed with the fancy compiler location printer, or in a
simpler way from the backends.
- All operators that might be subject to an error take a position as argument,
in order to print an informative message without relying on backtraces from
the backend
Ensuring messages don't print overlong lines still requires some manual work:
- if they don't contain any `Format` directives (`%` or `@`), use `"%a"
Format.pp_print_text` to turn word-wrapping on.
- otherwise replace spaces with `@ ` to mark possible cutting points, as soon
that it's possible the line will get over 80 chars (most often, this means
starting before the first `%a`)
Lots of tests have a new warning because they were calling subscopes without
using their outputs. A better solution could be to mark these subscopes as
`output`, now that it's possible !
