[Haskell-cafe] deepseq- missing Data.Map instance

Henry Laxen nadine.and.henry at pobox.com
Tue Nov 15 23:26:04 CET 2011

Dear Group,

Today I tried to compile snap 0.6 with ghc 7.2, (using virthualenv,
which is GREAT by the way) and got the following
error somewhere along the way got a message about aeson-native
requires deepseq- but I had deepseq- installed.  So I
unpacked aeson-native- in my virthualenv and changed the
build-depends to just deepseq which caused:

Configuring aeson-native-
Preprocessing library aeson-native-
Building aeson-native-
[2 of 6] Compiling Data.Aeson.Types ( Data/Aeson/Types.hs, 
dist/build/Data/Aeson/Types.o )

    No instance for (NFData Object)
      arising from a use of `rnf'
    Possible fix: add an instance declaration for (NFData Object)
    In the expression: rnf o
    In an equation for `rnf': rnf (Object o) = rnf o
    In the instance declaration for `NFData Value'
cabal: Error: some packages failed to install:
aeson-native- failed during the building phase. The exception was:
ExitFailure 1

A little investigating and I discovered that

instance (NFData k, NFData a) => NFData (Data.Map.Map k a) where
    rnf = rnf . Data.Map.toList

is in deepseq- but not in deepseq-  Adding it back got
aeson-native- and later snap-0.6 to compile just fine.  So I
guess my question is:  Is there a reason that the map instance was
removed from deepseq-, and can we please put it back in?

Best wishes,
Henry Laxen

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