Hello, Thanks to everyone who took time to comment on my notes. My & Isaac's previous post spawned a few separate discussions so I though I'd send a separate message to summarize the status of what has happened so far with regard to polymorphic components. * Rank-2 vs Rank-n types. I think that this is the most important issue that we need to resolve which is why I am placing it first :-) Here are our options: - option 1: Hugs style rank-2 types (what I described, very briefly) - option 2: GHC 6.4 style rank-2 types. As far as I understand, these are the details: * Based on "Putting Type Annotations to Work". * Predicative (type variables range only over simple (mono) types) We do not need to compare schemes for equality but, rather, we compare them for generality, using a kind of sub-typing. There * Notation for polymorphic types with explicit quantifiers. The main issue is if we should allow some corner case notational issues, such as empty quantifier lists, and quantified variables that are not mentioned in the type. - option 1: disallow these cases because they are likely to be accidental mistakes. - option 2: allow them because they make automatic program generation simpler. My initial proposal was suggesting 2 but I think that, having heard the arguments, I am leaning towards option 1. * Equality of schemes for labeled fields in different constructors. My suggestion did not seem to be too controversial. Stephanie is leaning towards a more semantic comparison of schemes. Indeed, just using alpha equivalence might be a bit too weak in some cases. Another, still fairly syntactic option, would be to pick a fixed order for the variables in quantifiers (e.g., alphabetic) for the purposes of comparison. * Pattern matching on polymorphic fields. This does not appear to be too controversial, although Atze had some reservations about this design choice. This is all that I recall, apologies if I missed something (if I did and someone notices, please post a replay so that we can keep track of what is going on). -Iavor