Type coercion failure when trying to &parse-from with begin(some_stream)

[bbannier]

While looking for a workaround for #1523 I ran into a type coercion failure I did not expect.

module foo;

global s = stream(b"\x00\x01\x02");

public type X = unit {
    x: uint8 &parse-from=begin(s);
};

$ spicyc -d foo.spicy
[error] foo.spicy:6:17-9:2: cannot coerce expression 'begin(foo::s)' of type 'iterator<stream>' to type 'value_ref<stream>'
[error] spicy-dump: aborting after errors

Here begin(s) should return an iterator<stream> which according to the docs can be passed to &parse-at.

[bbannier]

This should probably be rejected since &parse-from only accepts bytes.