[Haskell-beginners] questions about product types
anthony_clayden at clear.net.nz
Wed Jan 18 23:09:40 CET 2012
Tom Doris <tomdoris <at> gmail.com> writes:
> 3) In type theory, are product types consisting of distinct member types
considered special in any way? i.e. does the concept have a name and what
special properties do they have?
I don't know about type theory, but I've seen them called 'Type Indexed
Products'. See the HList Paper  section 7, which refers to .
I've found TIP's very successful in practice. They've gotten more rugged
through the gradual innovations in type inference that have been introduced
into GHC. (Especially the type equality constraint (~), which improves on
HList's TypeCast.) But the 'groundness issues' in HList section 9 still apply.
Using TIP's relies on overlapping instances (but _not_ necessarily Functional
Dependencies), so it's still a 'poor cousin' and (it seems) not to be
mentioned in polite company.
 Strongly Typed Heterogenous Collections, August 2004,
 Type-indexed Rows, POPL 2001, Shields/Meijer
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