Carter Schonwald
writes: indeed, this relates / augments record puns syntax already in GHC http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax- extns.html#record-puns.
Uh-oh. That documentation gives an example, and it exactly explains the weird type-level error I got when I tried to use the proposed syntax myself: Note that: * Record punning can also be used in an expression, writing, for example, let a = 1 in C {a} -- !!! instead of let a = 1 in C {a = a} The expansion is purely syntactic, so the expanded right-hand side expression refers to the nearest enclosing variable that is spelled the same as the field name. IOW the proposal _does_ conflict with existing syntax. (And I guess I can see a use for the example. Note that outside of that let binding, `a` would be a field selector function generated from the data decl in which field `a` appears -- that's the weirdity I got.) I suppose the existing syntax has a data constructor in front of the braces, whereas the proposal wants a term. But of course a data constructor is a term. So the proposal would be a breaking change. Rats! Is anybody using that feature?
On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson
gmail.com> wrote:
Unlike dot notation, this is unambiguous and doesn't conflict with any
existing syntax (AFAIK). ...