How to catch HyMacroExpansionError?

[weakish]

Tried:

• (import [hy.errors [HyMacroExpansionError]])
• try to catch HyTypeError, TypeError and Exception

All failed.

Example:

(import [hy.errors [HyMacroExpansionError]])

(defmacro foo [a] a)
(try (foo 1 2) (catch [e HyMacroExpansionError] (print "catched"))) ;; 1
(try (foo 1 2) (catch [e HyTypeError] (print "catched"))) ;; 2
(try (foo 1 2) (catch [e TypeError] (print "catched"))) ;; 3
(try (foo 1 2) (catch [e Exception] (print "catched"))) ;; 4
(try (foo 1 2) (catch [] (print "catched"))) ;;  5

1-5 all fails with throwing HyMacroExpansionError:

  (try (foo 1 2) (catch [e Exception] (print "catched"))) ;; 4
       ^-------^
HyMacroExpansionError: `foo' takes exactly 1 argument (2 given)

Tested on hy 0.10.1 (Python 2.7.6) and hy commit 42983d1 (Python Python 3.4.0)

[algernon]

I'm not sure you can catch this. Macro expansion happens at compile time, while try/catch at runtime. By the time Hy gets to the (try (catch ...)) block, the macro expansion already happened, failed, and raised an exception.

[refi64]

The reason is that macros get expanded before the program is run. Therefore, the exception occurs before the program even begins.

[weakish]

Thanks. Looking forward better debugging support for macros. #741

[emidln]

You could build your own defmacro that works inside a try/catch if you were so inclined.