This is a brain-dump of how container types and contexts work in the
new Pugs runcore.
Assuming everything other than an explicit method call is subject to
MMD, we have this desugaring:
# Sugared syntax
${$x} = 5;
# Desugared syntax
&infix:<=>(&circumfix:<${ }>($x), 5);
It's straightforward to type the relevant &infix:<=> part, given that
::Scalar, ::Array and ::Hash are roles that "does" the ::Ref role.
proto infix:<=> ((Ref of ::v) ::a is rw, ::v) --> ::a;
multi infix:<=> ((Scalar of ::v) ::a is rw, ::v) --> ::a {...}
However, what should the type of &circumfix:<${ }> be?
I'm currently going with:
proto circumfix:<${ }> (Any) --> (Scalar of Any) is rw;
multi circumfix:<${ }> ((Scalar of Any) ::a) --> ::a is rw {...}
That is, it applies to an argument that can yield a Scalar object when
used as a rvalue.
Below I'll use the notation value($x) to mean $x evaluated as an
rvalue, analogous to
the variable($x) special form for marking explicit lvalues.
Here is the signature for for prefix:<\>:
proto prefix:<\> (Any) --> (Ref of Any);
multi prefix:<\> (Ref ::T is rw) --> ::T {...}
multi prefix:<\> (::T) --> (Scalar of ::T) {...}
So these two are legal:
${ \3 }; # value(&prefix:<\>(3)) yields a
::Scalar container object
${ \$x }; # value(&prefix:<\>($x)) is just variable($x)
But these are not:
${ \3, }; # value(&prefix:<\>(&infix:<,>(3)))
yields a ::Tuple, not ::Scalar
${ variable($x) }; # value(variable($x)) means the same as value($x)
Thanks,
Audrey
