-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 8/28/10 06:17 , Patrick Browne wrote:
In the light of the above examples how should I interpret the class-to-subclass relation as logical implication? Is it a) If BEING then HUMAN (sufficient condition): BEING => HUMAN b) HUMAN is true only if BEING (necessary condition): HUMAN => BEING c) Neither?
(b). But there's an additional wrinkle: what it really says is "A HUMAN is (...). Oh, and it's a BEING too." Which is to say, Haskell doesn't look at BEING until *after* it's decided something is a HUMAN. (Technically speaking, constraints are not used when selecting an instance; they're applied after the fact, and if the selected instance doesn't conform then it throws a type error.) - -- 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/ iEYEARECAAYFAkx5KOcACgkQIn7hlCsL25UWyQCfTblcgeEfwOci9KE7leVs07aN VT4AoJAwHqXoD6nbD+TZVRlAWj3N99SM =jA0B -----END PGP SIGNATURE-----