Compiling on windows about hasktorch

[davidbelius]

Recording my findings here for the benefit of others with the same question:

• After removing the unix dependency from examples/examples.cabal, "cabal build hasktorch" runs for a pretty long time, but eventually fails with ld complaining about among others -ltorch.
• One may hope that pointing cabal to libtorch windows binaries using --extra-lib-dirs will fix this, but it did not, as far as I understand because:
• libtorch binaries are compiled using MSVC and are not "ABI-compatible", which means GHC's c compiler mingw can not link to them (see the "tip" on https://pytorch.org/cppdocs/installing.html).
• One may hope to compile libtorch from source on windows using mingw, but libtorch does not provide makefiles for mingw. I did not attempt to figure it out myself after reading https://discuss.pytorch.org/t/can-i-build-libtorch-from-source-with-mingw/52632.

So getting hasktorch to compile on windows unfortunately seems like a major undertaking, even with just cpu and without cuda support.

[junjihashimoto]

Hi @davidbelius,
I think that when we use MSVC's libtorch, we need to use ghc of MSVC(https://www.reddit.com/r/haskell/comments/n0xcoy/announce_experimental_windows_ghc_8105_binary/), and some patches for some packages.
This repository(https://github.com/awson/ghc-nw) provides the paches.
However, both of them are not maintained.
I recommend to use WSL on windows, although the performance will be worse than native linux. GPU also works.