Auto-promotion now occurs in only two cases: when we start the compiler and when we expand a macro. It's fully recursive so even a non-model nested in a model will be promoted.
This change fixes some regressions induced by the stricter type checks of the pattern-matching compiler.
It's rarely useful, because it catches all exceptions, but it doesn't let you do anything other than return `None`. You can still get the same effect with `(except [])`.
The implementation of `hy.core.language.exec` draws code from the `exec_` function in commit f574c7be6ebc80041ef58ca29588f310248ebed4 of the library Six, which is copyright 2010–2017 Benjamin Peterson and licensed under the Expat license.
I've added shadow versions of many operators that didn't have one. And, I've changed the behavior of various binary operators with more or fewer than 2 arguments to make the shadow and real versions more consistent and to make the behavior more logical in either case. For details, see the additions to NEWS and the new file tests/native_tests/operators.hy, which simultaneously tests shadow and real operators.
Although there are a lot of changes, I've put them all in one commit because they're interdependent.
* with-decorator: Allow a `setv` form as the form to be decorated
This feature is of dubious value by itself, but it's necessary to allow `defn` to create a lambda instead of a `def`.
* Make `fn` work the same as `lambda`
That is, allow it to generate a `lambda` instead of a `def` statement if the function body is just an expression.
I've removed two uses of with_decorator in hy.compiler because they'd require adding another case to HyASTCompiler.compile_decorate_expression and they have no ultimate effect, anyway.
In a few tests, I've added a meaningless statement in `fn` bodies to force generation of a `def`.
I've removed `test_fn_compiler_empty_function` rather than rewrite it because it seems like a pain to maintain and not very useful.
* Remove `lambda`, now that `fn` does the same thing
