The caching doesn't seem to work properly any more with Hakyll 4.5.1.0 and GHC 7.8.2. Everything gets rebuilt every time, which makes using "./hakyll watch" harder.

Steps to reproduce (with my website code):

ghc -O2 hakyll.hs -o hakyll
./hakyll clean
./hakyll build # <builds everything>
./hakyll build # <builds everything again>

I tried it with older versions of my hakyll.hs file that definitely worked back on GHC 7.6.2, and the bug persisted. I also think I used to be on an older version of the Hakyll package itself, so it could be either a difference in the package or a difference in GHC.

I haven't tried with older versions of Hakyll, but I could do that if it seems useful.

Thanks for looking at this.