Could template-Haskell be used somehow? - Lyndon Maydwell On Mar 10, 2012 4:50 AM, "Clark Gaebel" wrote:

In Haskell, what's the canonical way of declaring a top-level array (Data.Vector of a huge list of doubles, in my case)? Performance is key in my case.

The straightforward way would just be something like:

globalArray :: V.Vector Double globalArray = V.fromList [ huge list of doubles ] {-# NOINLINE globalArray #-}

However, I don't want to have to run the fromList at runtime. Not only would this mean a bigger executable (having to store a linked list, instead of an array), it would be quite inefficient since we don't even use the source list!

Therefore, I was thinking of storing the array in a C file:

static const double globalArray[] = { huge list of doubles }; double* getGlobalArray() { return globalArray; } int getGlobalArraySize() { return sizeof(globalArray)/sizeof(globalArray[0]); }

And importing it in haskell witht he FFI, followed with an unsafeCast:

foreign import ccall unsafe "getGlobalArray" c_globalArray :: Ptr CDouble foreign import ccall unsafe "getGlobalArraySize" c_globalArraySize :: CInt

globalArray :: V.Vector Double globalArray = V.unsafeCast $ unsafeFromForeignPtr0 (unsafePerformIO $ newForeignPtr_ c_globalArray) (fromIntegral c_globalArraySize) {-# NOINLINE globalArray #-}

But this version (clearly) is full of "unsafe"ty. Is there a better way that I haven't thought of?

Regards, - clark

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Clark Gaebel writes:

In Haskell, what's the canonical way of declaring a top-level array (Data.Vector of a huge list of doubles, in my case)? Performance is key in my case.

The straightforward way would just be something like:

globalArray :: V.Vector Double globalArray = V.fromList [ huge list of doubles ] {-# NOINLINE globalArray #-}

However, I don't want to have to run the fromList at runtime.

I think GHC will convert it to an array (and in general evaluate constants) at compile time (probably requires -O). -k