[perl #128108] Feature request - improvements to named parameter handling

[via RT]

# New Ticket Created by  David Warring 
# Please include the string:  [perl #128108]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=128108 >


Rakudo is pretty good at parsing literal arguments as positional parameters. 
For example:

    multi sub s(True) { 'case1' }    # Bool $ where $_
    multi sub s('fred') { 'case2' }  # Str $ where 'fred'
    multi sub s(42) {'case3' }       # Int $ where 42

    for 1+1==2, 'fred', 42 -> $val {
        say s($val)
    }
    #case1
    #case2
    #case3

If I refactor the above from a positional to a named parameter, then I need to 
be a bit more explicit. Something like:

    multi sub s(Bool :$val! where $_) { '#case1'  }
    multi sub s(Str :$val! where 'fred') { '#case2' }
    multi sub s(Numeric :$val! where 42) { '#case3' }

    for 1+1==2, 'fred', 42 -> $val {
        say s(:$val)
    }

Can the handling of named arguments be improved to more like the positional 
case? I was hoping for something like:

    multi sub s(:val) { "#case1" }
    multi sub s(:val<fred>) { "#case2" }
    multi sub s(:val(42)) { "#case3" }

Or something similar (None of these parse at the moment).