From @bbkr

Rakudo 2012.09

$ perl6 -e 'Failure.new("foo").();'
No such method 'throw' for invocant of type 'Str'
  in method <anon> at src/gen/CORE.setting​:9914
  in at src/gen/Metamodel.pm​:2380
  in any find_method_fallback at src/gen/Metamodel.pm​:2368
  in any find_method at src/gen/Metamodel.pm​:922
  in at src/gen/BOOTSTRAP.pm​:827
  in any at src/gen/BOOTSTRAP.pm​:811
  in block at -e​:1

Those LTA errors can be avoided by adding Exception (or some kind of "throwable" if there is any) type check to Failure constructor.

From @usev6

Locally I simply added a type constraint to method new for class Failure​:

$ diff src/core/Failure.pm Failure.pm.orig
5c5
< method new(Exception $exception) { self.bless(​:$exception) }

method new\($exception\) \{ self\.bless\(​:$exception\) \}

With that change the error message became​:

$ perl6 -e 'Failure.new("foo").();'
Type check failed in binding $exception; expected 'Exception' but got 'Str'
  in method new at src/gen/m-CORE.setting​:15706
  in block <unit> at -e​:1

Would that be good enough?

@usev6 - Status changed from 'new' to 'open'

From @usev6

I added a test to S04-exceptions/fail.t with commit Raku/roast@4366d917a5 and created a pull request for Rakudo​: rakudo/rakudo#442

From @usev6

The test passes now. I'm closing this ticket as 'resolved'.

@usev6 - Status changed from 'open' to 'resolved'