使用Numeric.FFT时没有（Data.Vector.Generic.Base.Vector Data.Vector.Unboxed.Vector Double）的实例

Question

EDIT: Solution : The solution to the problem was to specify the correct vector library in a .cabal file. The tell-tale sign (kindly pointed out by @Daniel below) was that the exact version of the vector was referenced in the error message. Indeed my file was building against vector-0.10.something while vector-fftw was compiled against vector-0.9.1.

---

I am trying to use the fftw-vector library but am stuck with this type error:

-- test.hs
import qualified Numeric.FFT.Vector.Invertible as FFTI
import qualified Data.Vector.Unboxed as U

z = FFTI.run FFTI.dct1 U.empty

main = putStrLn "Won't compile"

This is the error message:

No instance for (vector-0.9.1:Data.Vector.Generic.Base.Vector
                   U.Vector Double)
  arising from a use of `FFTI.run'
Possible fix:
  add an instance declaration for
  (vector-0.9.1:Data.Vector.Generic.Base.Vector U.Vector Double)
In the expression: FFTI.run FFTI.dct1 U.empty
In an equation for `z': z = FFTI.run FFTI.dct1 U.empty

but as far as I can tell there is actually an instance of Data.Vector.Gener.Base.Vector for Data.Vector.Unboxed Double (Link) (guess I am wrong).

This is with ghc-7.6.1, vector-0.9.1 and vector-fftw .

(I had to make two tiny changes to vector-fftw so it compiles with base 4.6 and ghc-7.6.1, but that should be unrelated ...)

thank you

EDIT:

two changes I made to vector-fftw:

--- a/Numeric/FFT/Vector/Base.hsc
+++ b/Numeric/FFT/Vector/Base.hsc
@@ -34,10 +34,11 @@ import Control.Monad.Primitive (RealWorld,PrimMonad(..),
 import Control.Monad(forM_)
 import Foreign (Storable(..), Ptr, unsafePerformIO, FunPtr,
                 ForeignPtr, withForeignPtr, newForeignPtr)
-import Foreign.C (CInt, CUInt)
+-- import Foreign.C (CInt, CUInt)
 import Data.Bits ( (.&.) )
 import Data.Complex(Complex(..))
 import Foreign.Storable.Complex()
+import Foreign.C.Types



diff --git a/vector-fftw.cabal b/vector-fftw.cabal
index 5ca7c46..0436834 100644
--- a/vector-fftw.cabal
+++ b/vector-fftw.cabal
@@ -40,7 +40,7 @@ Library
   Other-modules:
         Numeric.FFT.Vector.Base

-  Build-depends: base>=4.3 && < 4.6, vector==0.9.*, primitive==0.4.*,
+  Build-depends: base>=4.3 && < 4.7, vector==0.9.*, primitive>=0.4 && < 0.6,
                  storable-complex==0.2.*

Answer 1

Note that the error message specifies the specific version of the package that defines the class an instance is missing for:

No instance for (vector-0.9.1:Data.Vector.Generic.Base.Vector
                   U.Vector Double)

That usually means that one of the used packages was compiled against a different version than the one currently used in the project.

I don't see how exactly this would arise, but check for broken packages with ghc-pkg check , and verify that your packages have the correct ids with ghc-pkg describe vector and ghc-pkg describe vector-fftw , possibly vector was rebuilt after building vector-fftw . and the package hashes do not match.