-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On 20/10/15 13:23, Joachim Breitner wrote: > This is expected. If there is any ? in the type, then GHC wants > all variables to be properly bound. This is not related to whether > a is used or not: I see. I still think the error message could be more specific though...
>> 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.) > You mean type constraints involving an otherwise unused type > variable? This seems to be unrelated to the question of foralls. It is. It just hit me while reading through my email before sending it. > But indeed the 2010 report writes “The context cx must only contain > type variables referenced in t.” > https://www.haskell.org/report/node/2010/haskellch4.html#x10-660004.1.3 > > and even with -XHaskell2010, this is accepted. Then I understood it correctly. I think we should fix this. > Might be worth a ticket, although I would not be surprised if some > of the type class hackers around here finds a use case for this > :-) If there is a usecase for this, it could be a pragma. GHC should not accept it by default though. - -- Alexander [email protected] https://secure.plaimi.net/~alexander -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCgAGBQJWJiUfAAoJENQqWdRUGk8BwE8QALSsg6Tn0Xet7v4uJ6xRj2Hi Ai2D70snCRi3kVrIbtwN3ZiOQfmLPTqQbohfICMac1AwWA8P9QQ+FKvii5UNh9SG 0YdAOp6SFyIrKU9SobfEiDSM4D2KZJ/6JsJFh4nmmDQWneA7YgGM1Gk2zFlMiW1e oYyERM3qTcMKo1g/qwQOEIvGiWhdbxBQ04NbuOf+cSLAb/rKeBEylzG7dbmtCJeN LFUZPwMOUNFSSXvaM5xGzeSppd+dxEd1zk9JR2lm0Q4J8gRfz3Upibi7tWDtJnia IW0znMAPRXdcjxaonXsmUC1rK+Ub9Ey3Bt0lR37BzCUaAmvYgVfvzhRyDSLUrpFA ym2sBGn75dfWJuor9kbeoQ1kRg1wPrZy9B6/4u7DBFWU2HnSreH6x/Izu741QSdZ 9xXT5caU1H/W76CybbBvnH8IUjv76SP9b83rYBFc0r/JhK3+r/nODckTrif1zAh9 2WOq6q1lo30/bURcNcx0qLZoCoOFmQtOpFTOOD84yCWAfrZ2Ybnnh8Eh/7cd5JQo 8/dIW9wFJCSBL9rX9PbuYygTEPaUHNR099QRZ5LBRp39NjFR/t+Z/gnHpnivxsz0 p12aOPbTNxCbctoeLNE2S/sw9ZDEWnTupUqhF8QLvZieVaznnqwNcsGXUd/qYPP8 Y2l0+sojeWyk8XNKNz+m =nxvb -----END PGP SIGNATURE----- _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
