-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 In Set theory sentence construction, if the letter is not used then no foul. In Haskell, it is not always so. The following is well-typed and works happily: f :: Eq a => b -> b f b = b However, this does not work: f :: ∀ a. Eq a => b -> b f b = b It will result in the error "Not in scope: type variable ‘b’" being spat out twice. Is this error message really desirable? If there is no principled reason for this result, may I suggest improving it? I can conceivably see some codebase using RankNTypes exclusively having a typo like f :: ∀ a. b -> b f b = b Consequently the error message should be more precise. Furthermore the first code snippet I gave also strikes me as nonsensical; if someone has code like that, it is probably the result of a typo. Should we really permit it? Is there a motivating reason for permitting it? If no, I suggest it be an error. (My understanding of the 2010 report was that it *isn't* permitted, but perhaps I read it wrong.) - -- Alexander alexander@plaimi.net https://secure.plaimi.net/~alexander -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCgAGBQJWJiE0AAoJENQqWdRUGk8BVmYP/0yhrfFs8LHLUAhGnza3f6Xx uFJQdvMmZcSLQQZxFyBvVcNwAK0x1ntnT+jeG/Q0j1oQns6EoWkJ9WzBQIxVQ2+O 9bm45N+gX1K1W1Z0WEX+LCPszntLMvBdp6C3Wp4ff+XvS9e0uHTqftDdD3iUexPA K5wTB5qs+3IWVFEyyPIuJpOqOLhTy9FMct9Ls4m72Uu3FIWPEgjANuT/WkkLASXP Av+qn0hTUzmoNf2nWcjvJQIZvgM6xfpJleWlO2CinOuPunZiackja/qTGlvx7Pu6 Yo5Fs2WdfCB1yx3iPnDcSrJ3pQcZkLqVsGRNdEXdQEHMH1icLR15Z7ynpKkI6uBb JI+vAyq//NbdbRUOPzwN/PA+kGczUTBhTeAnwB5194fdzlfmH9vDsdN8p4CPtsTG 3T3u5EEyn8a/v0nQPssDEfli8Mx4uOswQmTsLgJCJ1H94FbNdGS3R98NmM63A9II rN53o16m6z4C27YQL4q84LwbnWvOEyE9s3xBZMd8hsbTdb7F2syVoSYZazgP5PGc uv/pAwKqwkGU53yBBhj+RqfPXk3qf0bOHtsercIAhnmkIAjI5l7bdxmDyhW4aj49 pWRJgOPAAlQ+VriFoodMZ9PD42pvxUlzicDfvpELVpviHdlTrovky9UC+buCFrtG 7k9GmyHqe/B3LyDjxbh+ =jerq -----END PGP SIGNATURE-----