PROPOSAL: Include record puns in Haskell 2011

Simon Peyton-Jones simonpj at
Thu Feb 25 03:33:47 EST 2010

| >> we implicitly get
| >> f :: T -> Int
| >> which punning shadows with
| >> f :: Int	
| >> whereas I generally avoid shadowing completely.
| >
| > I agree with Ian.
| I tend to agree.

I originally had field puns in GHC, and then took them out when Haskell 98 removed them, after a discussion very like this one.  I put them back in because some people really wanted them.  

Actually GHC has three separate extensions to do with named fields:

	field disambiguation (Section 7.3.14)
	field puns (Section 7.3.15)
	field wildcards (Section 7.3.16)

Look here

Opinions differ.  I'm rather with John: let the programmer choose, rather than enforcing a style in the language. For punning, the programmer can certainly choose on a case by case basis.  If you use Haskell 98's existing syntax, there is no change to the semantics if you switch on field puns:

	data T = C { f :: Int }

	foo (C {f = x}) = ...   -- No punning
	bar (C {f})     = ...	-- Punning

It would help this discussion if someone created a ticket to explain the actual proposal, so that we are all discussing the same thing.


More information about the Haskell-prime mailing list