Right. What I meant is that with -XMonomorphismRestriction, it compiles with with both -XMonoLocalBinds and -XNoMonoLocalBinds.
That means that MonoLocalBinds can not be solely responsible for this behaviour. Anyway, I just noticed that a very similar example (using Read) is described in the Haskell report's section on the monomorphism restriction. Roman * Erik Hesselink <hessel...@gmail.com> [2012-11-11 16:43:20+0100] > That's strange. Here, it only fails with both NoMonomorphismRestriction and > NoMonoLocalBinds (which makes sense). I've tested on 7.4.1 and 7.6.1. > > Erik > > > On Sun, Nov 11, 2012 at 3:54 PM, Roman Cheplyaka <r...@ro-che.info> wrote: > > > Apparently not — the code comilers with any of -XNoMonoLocalBinds and > > -XMonoLocalBinds, but not with -XNoMonomorphismRestriction. > > > > * wagne...@seas.upenn.edu <wagne...@seas.upenn.edu> [2012-11-09 > > 14:07:59-0500] > > > It's possible that the below blog post is related. > > > ~d > > > > > > http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 > > > > > > Quoting Roman Cheplyaka <r...@ro-che.info>: > > > > > > >For this module > > > > > > > > module Test where > > > > > > > > import System.Random > > > > > > > > data RPS = Rock | Paper | Scissors deriving (Show, Enum) > > > > > > > > instance Random RPS where > > > > random g = > > > > let (x, g') = randomR (0, 2) g > > > > in (toEnum x, g') > > > > randomR = undefined > > > > > > > >ghc (7.4.1 and 7.6.1) reports an error: > > > > > > > > rand.hs:9:9: > > > > No instance for (Random t0) arising from the ambiguity check > > for g' > > > > The type variable `t0' is ambiguous > > > > Possible fix: add a type signature that fixes these type > > variable(s) > > > > Note: there are several potential instances: > > > > instance Random RPS -- Defined at rand.hs:7:10 > > > > instance Random Bool -- Defined in `System.Random' > > > > instance Random Foreign.C.Types.CChar -- Defined in > > `System.Random' > > > > ...plus 34 others > > > > When checking that g' has the inferred type `g' > > > > Probable cause: the inferred type is ambiguous > > > > In the expression: let (x, g') = randomR (0, 2) g in (toEnum x, > > g') > > > > In an equation for `random': > > > > random g = let (x, g') = randomR ... g in (toEnum x, g') > > > > Failed, modules loaded: none. > > > > > > > >There should be no ambiguity since 'toEnum' determines the type of x > > > >(Int), and that in turn fixes types of 0 and 2. Interestingly, > > > >annotating 0 or 2 with the type makes the problem go away. > > > > > > > >jhc 0.8.0 compiles this module fine. > > > > > > > >Roman > > > > > > > >_______________________________________________ > > > >Glasgow-haskell-users mailing list > > > >Glasgow-haskell-users@haskell.org > > > >http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > > > > > > > > > > > > > > > > > _______________________________________________ > > > Glasgow-haskell-users mailing list > > > Glasgow-haskell-users@haskell.org > > > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > > > > _______________________________________________ > > Glasgow-haskell-users mailing list > > Glasgow-haskell-users@haskell.org > > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
