-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 7/26/10 06:02 , John Lato wrote:
If the behavior of class contexts on data types were changed to what you think it should mean, i.e. contexts specified in a data declaration are carried around for all uses of that type instead of just the data constructor, I wouldn't mind at all. Whether this is a good idea or would cause other problems, I can't say.
As I understand it: 1) carrying them around complicates Haskell98 (and now Haskell2010) compatibility (also see below); 2) GADTs do what you want, since they don't have backward compatibility baggage. As to the current proposal, I think nobody's certain what would happen to older programs if data were changed to carry contexts around --- someone might be relying on the current behavior, and changing it might produce runtime oddness instead of a compile-time error --- whereas making contexts illegal will produce an easily-fixed error message in all relevant cases. - -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkxNo5EACgkQIn7hlCsL25WDzgCdE/QmWy/Do1M73n+rt829Dyb7 HuMAni+vw//HuanYc4LJ5uXPYdPDBmuu =/ivE -----END PGP SIGNATURE-----