- An new simp attribute may depend on other existing attributes
- Add `[norm]` simp attribute. It is an extension of the default `[simp]` attribute.
It should be used to add extra rules for normalizing goals.
These extra rules are used to produce normal forms and/or reduce the
number of constants used in a goal. Here is an example coming from a
discussion with @kha. When working with monads, we may want to
eliminate `<$>` by using the lemma `f <$> x = x >>= pure ∘ f`.
This lemma is in the `[norm]` simp set, but it is not in `[simp]`
On OSX, Lean was often crashing when using trace messages.
I identified a problem in the thread finalization process.
In OSX, the `silent_ios_helper` at `library/trace.cpp` was being
finalized after the `null_streambuf` at `util/null_ostream.cpp`.
There was also a memory corruption problem also related to
`null_streambuf`.
This commit fixes this problem by using the following recipe
for creating null output stream buffers in C++.
https://stackoverflow.com/questions/11826554/standard-no-op-output-stream
@kha: I decided to implement this change before I start the
type_context modifications. The change did not affect the corelib and
test suite much. The only annoying problem is that `out` cannot be
used to name locals anymore.
The new test exposes the problem. Before this commit, the common
subexpressions at
```
def tst : tree → nat
| (tree.leaf v) := v
| (tree.node v l r) :=
match f v with
| tt := tst l + tst l - tst l -- <<< HERE
| ff := tst r
end
```
were not converted into a let-exprs.
We use the auxiliary procedure pull_nested_rec_fn to pull recursive
application in nested match expressions. This is needed because the
nested match expression is compiled before we process the recursive
procedure that contains it. This transformation may produce
performance problems if the recursive application does not depend on
the data being matched. Here is an example from the new test:
```
def tst : tree → nat
| (tree.leaf v) := v
| (tree.node v l r) :=
match f v with
| tt := tst l
| ff := tst r
end
```
pull_nested_rec_fn will convert it into
```
def tst : tree → nat
| (tree.leaf v) := v
| (tree.node v l r) := tst._match_1 (f v) (tst l) (tst r)
```
Since our interpreter uses eager evaluation, both `(tst l)` and `(tst r)`
are executed. This commit fixes this issue by expanding `tst._match_1`
during code generation.
