The equation compiler uses different strategies for processing
recursive equations. Some of them may produce unclear runtime cost
model. For example, the following fibonacci functions was running in
linear time instead of exponential time because the equation compiler
used the brec_on recursor.
def fib : nat → nat
| 0 := 1
| 1 := 1
| (n+2) := fib (n+1) + fib n
@dselsam and @jroesch have reported examples were the equation compiler
produces a negative performance impact. The new test (`eval` function)
captures the problem reported by @jroesch. In this example, the runtime
should not depend on the "amount of fuel".
This commit addresses this issue.
Motivations:
- Clear execution cost semantics for recursive functions.
- Auxiliary meta definition may assist recursive definition unfolding in the type_context object.
Next step: use meta auxiliary definition at code generation.
TODO: we are not checking if the unicode escape values provide by the
user correspond to valud unicode scalar values. We should check how
other languanges handle this case.
for ordered_cancel_comm_monoid. The change to partial_order, with a derived lt relation, makes the lt axioms of ordered groups derivable with no additional assumptions.
closes#1175
The types `string_imp` and `string.iterator_imp` were supposed to be
marked private, but we cannot do it because we need to provide
`string_imp.mk`, `string_imp.cases_on`, `string.iterator_imp.mk` and
`string.iterator_imp.cases_on` in the VM since we use a different
internal representation. Note that marking them as private does not
work since users can still access `string_imp.cases_on` using
meta-programming.
So, we need better support for private declarations.
Missing feature, char literals do not support non ASCII values.
That is, in the current implementation, we cannot write 'α'.
This will be implemented in the future.
The VM native implementation does not behave correctly for huge
strings (i.e., strings with more than 4G characters).
The problem is that the current implementation relies on
```
size_t force_to_size_t(vm_obj const & o, size_t def)
```
We may also have overflow problems in the string.iterator implementation
code. This is not a big deal right now, since I doubt we will try
to process string with more than 2^32 characters.
@Kha the `core_lib` and tests seem to be working correctly, but
we need more tests.
Comment from parser.h
This commit makes sure that all declaration parameters must be surrounded with some kind of bracket. (e.g., '()', '{}', '[]').
The goal is to avoid counter-intuitive declarations such as:
example p : false := trivial
def main proof : false := trivial
which would be parsed as
example (p : false) : _ := trivial
def main (proof : false) : _ := trivial
where `_` in both cases is elaborated into `true`. This issue was raised by @gebner in the slack channel.
Remark: we still want implicit delimiters for lambda/pi expressions. That is, we want to write
fun x : t, s
or
fun x, s
instead of
fun (x : t), s
