The following call sequence is possible:
C++ -> Lua -> C++ -> Lua -> C++
The first block of C++ is the Lean main function.
The main function invokes the Lua interpreter.
The Lua interpreter invokes a C++ Lean API.
Then the Lean API invokes a callback implemented in Lua.
The Lua callback invokes another Lean API.
Now, suppose the Lean API throws an exception.
We want the C++ exception to propagate over the mixed C++/Lua call stack.
We use the clone/rethrow exception idiom to achieve this goal.
Before this commit, the C++ exceptions were converted into strings
using the method what(), and then they were propagated over the Lua
stack using lua_error. A lua_error was then converted into a lua_exception when going back to C++.
This solution was very unsatisfactory, since all C++ exceptions were being converted into a lua_exception, and consequently the structure of the exception was being lost.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
copy_values is not a big if-then-else anymore.
Before this change, whenever we added a new kind of userdata, we would have to update copy_values.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Lua API is an integral part of Lean. It does *not* have the same status
of external APIs (e.g., Python) we will add in the future.
We will reserve the directory bindings for external APIs for using Lean
as a library.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
