Hey all, While trying to get a commit pushed for Yesod[1], Alexander Dunlap pointed out one of his programs didn't work with the new code. After some investigation, I was able to reproduce the bug with the following code snippet: {-# LANGUAGE TypeFamilies #-} data family Foo a data Bar = Bar data instance Foo Bar = Bar1 | Bar2 | Bar3 | Bar4 | Bar5 | Bar6 | Bar7 | Bar8 | Bar9 deriving Eq This produces: Couldn't match expected type `Main.R:FooBar' against inferred type `Foo Bar' NB: `Foo' is a type function In the first argument of `Main.$con2tag_R:FooBar', namely `a' In the expression: (Main.$con2tag_R:FooBar a) In the expression: case (Main.$con2tag_R:FooBar a) of { a# -> case (Main.$con2tag_R:FooBar b) of { b# -> (a# GHC.Prim.==# b#) } } The especially strange thing about this bug is that it only occurs when there are more than 8 constructors; if I remove Bar9, everything seems to work. Does anyone have experience with this occuring? Michael [1] http://docs.yesodweb.com/blog/please-break-yesod/
Hmm, strange. I have a project that uses data families with dozens of
constructors per "clause"/instantiation of the type function. I use GADT
syntax to define them though as they also refine one of the parameter type
variables. Never had any issues with it, although I haven't tried building
that project on GHC 7 yet (as some of its dependencies didn't work last time
I tried), so maybe it's a new issue?
On Sun, Nov 14, 2010 at 2:15 PM, Michael Snoyman
Hey all,
While trying to get a commit pushed for Yesod[1], Alexander Dunlap pointed out one of his programs didn't work with the new code. After some investigation, I was able to reproduce the bug with the following code snippet:
{-# LANGUAGE TypeFamilies #-} data family Foo a data Bar = Bar data instance Foo Bar = Bar1 | Bar2 | Bar3 | Bar4 | Bar5 | Bar6 | Bar7 | Bar8 | Bar9 deriving Eq
This produces:
Couldn't match expected type `Main.R:FooBar' against inferred type `Foo Bar' NB: `Foo' is a type function In the first argument of `Main.$con2tag_R:FooBar', namely `a' In the expression: (Main.$con2tag_R:FooBar a) In the expression: case (Main.$con2tag_R:FooBar a) of { a# -> case (Main.$con2tag_R:FooBar b) of { b# -> (a# GHC.Prim.==# b#) } }
The especially strange thing about this bug is that it only occurs when there are more than 8 constructors; if I remove Bar9, everything seems to work. Does anyone have experience with this occuring?
Michael
[1] http://docs.yesodweb.com/blog/please-break-yesod/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Hmm. It works with HEAD (and hence I believe with the 7.0.1 RC2). It looks similar to http://hackage.haskell.org/trac/ghc/ticket/4174, which is fixed. Anyway I've added it as a regression test, so it should never go wrong again. Thanks for mentioning it. Simon | -----Original Message----- | From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On | Behalf Of Michael Snoyman | Sent: 14 November 2010 19:16 | To: Haskell Cafe | Subject: [Haskell-cafe] Curious data family bug | | Hey all, | | While trying to get a commit pushed for Yesod[1], Alexander Dunlap | pointed out one of his programs didn't work with the new code. After | some investigation, I was able to reproduce the bug with the following | code snippet: | | {-# LANGUAGE TypeFamilies #-} | data family Foo a | data Bar = Bar | data instance Foo Bar | = Bar1 | Bar2 | Bar3 | Bar4 | Bar5 | Bar6 | Bar7 | Bar8 | Bar9 | deriving Eq | | This produces: | | Couldn't match expected type `Main.R:FooBar' | against inferred type `Foo Bar' | NB: `Foo' is a type function | In the first argument of `Main.$con2tag_R:FooBar', namely `a' | In the expression: (Main.$con2tag_R:FooBar a) | In the expression: | case (Main.$con2tag_R:FooBar a) of { | a# | -> case (Main.$con2tag_R:FooBar b) of { | b# -> (a# GHC.Prim.==# b#) } } | | The especially strange thing about this bug is that it only occurs | when there are more than 8 constructors; if I remove Bar9, everything | seems to work. Does anyone have experience with this occuring? | | Michael | | [1] http://docs.yesodweb.com/blog/please-break-yesod/ | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe
Sorry, I forgot to mention which compiler I was working with: 6.12.3.
I'm glad to hear it's working with 7.
Michael
On Mon, Nov 15, 2010 at 4:58 PM, Simon Peyton-Jones
Hmm. It works with HEAD (and hence I believe with the 7.0.1 RC2). It looks similar to http://hackage.haskell.org/trac/ghc/ticket/4174, which is fixed.
Anyway I've added it as a regression test, so it should never go wrong again. Thanks for mentioning it.
Simon
| -----Original Message----- | From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On | Behalf Of Michael Snoyman | Sent: 14 November 2010 19:16 | To: Haskell Cafe | Subject: [Haskell-cafe] Curious data family bug | | Hey all, | | While trying to get a commit pushed for Yesod[1], Alexander Dunlap | pointed out one of his programs didn't work with the new code. After | some investigation, I was able to reproduce the bug with the following | code snippet: | | {-# LANGUAGE TypeFamilies #-} | data family Foo a | data Bar = Bar | data instance Foo Bar | = Bar1 | Bar2 | Bar3 | Bar4 | Bar5 | Bar6 | Bar7 | Bar8 | Bar9 | deriving Eq | | This produces: | | Couldn't match expected type `Main.R:FooBar' | against inferred type `Foo Bar' | NB: `Foo' is a type function | In the first argument of `Main.$con2tag_R:FooBar', namely `a' | In the expression: (Main.$con2tag_R:FooBar a) | In the expression: | case (Main.$con2tag_R:FooBar a) of { | a# | -> case (Main.$con2tag_R:FooBar b) of { | b# -> (a# GHC.Prim.==# b#) } } | | The especially strange thing about this bug is that it only occurs | when there are more than 8 constructors; if I remove Bar9, everything | seems to work. Does anyone have experience with this occuring? | | Michael | | [1] http://docs.yesodweb.com/blog/please-break-yesod/ | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe
participants (3)
-
Daniel Peebles -
Michael Snoyman -
Simon Peyton-Jones