From amoc.yn@gmail.com

<amoc> rakudo​: my :​:MyType :​:= :(Num, Str)
<p6eval> rakudo c26021​: OUTPUT«ResizablePMCArray​: Can't pop from an empty
array!␤current instr.​: 'parrot;Perl6;Grammar;Actions;typename' pc -3015048
((unknown file)​:-1)␤»

<amoc> rakudo​: :​:MyType :​:= :(Num, Str)
<p6eval> rakudo c26021​: OUTPUT«too few arguments passed (0) - 2 params
expected␤current instr.​: '_block14' pc 40 (EVAL_18​:28)␤»

<amoc> rakudo​: :​:MyType := Int
<p6eval> rakudo c26021​: RESULT«Int»

<jnthn> rakudo​: :​:MyType := Int; my MyType $x = 42; say "ok"; $x = "OMG";
say $x;
<p6eval> rakudo c26021​: OUTPUT«ok␤Type mismatch in assignment.␤current
instr.​: 'die' pc 15960 (src/builtins/control.pir​:204)␤»

but from​: http://perlcabal.org/syn/S02.html#Names_and_Variables

A signature object (Signature) may be created with colon-prefixed parens​:
  my :​:MySig :​:= :(Int, Num, Complex, Status)

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

From @bbkr

NOM

bbkr​:nom bbkr$ ./perl6 -e 'my :​:MyType :​:= :(Num, Str)'
===SORRY!===
Malformed my at line 1, near "​::MyType :"

From @moritz

It now parse-errors as it should, and not with an internal error message
(though not quite in the way that STD does it). Closing now.

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