"It's something that would be easy to test at compile-time, ergo it must be tested at compile-time".
Maybe the edge case that it's not possible to decide at compile-time if this hash %h = ( key => @arr ) has a well-formed list at RHS with an even number of elements (how many elements will @arr have ???) makes it not so easy to test it generally at compile-time?
A good work-around might be to throw a warning if arrays are used as hash-values after a fat comma... I would really like it this way, since list-flattening in values really seems too "odd" to me!
