Performance improvements

[m-col]

Performance is pretty terrible currently but can definitely be improved. Things to look at:

• are lazy types used in all places where they could/should be? Some things may not be needed ever, e.g. if they are not used in templates (specifically thinking about bytestrings)
• does the code generate any crazy hunks
• are any unnecessary code paths being traversed all the time
• getCommits can be improved
• detect file changes in diffs for new commits and only re-render those files
• fixupLists and the diff list logic could probably be improved too

gotta profile

[m-col]

Reading resources:

• https://wiki.haskell.org/Performance
• https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/profiling.html
• http://book.realworldhaskell.org/read/profiling-and-optimization.html

[m-col]

I played around with some different sinks into which ginger rendered data to see what differences are observed. Here are the rough results. The numbers are the seconds it took to render gitserve's and qtile's data using the docs template.

• IORef: 63 63 64 63 65 63
• Writer Text: 94 95 152 161
• Writer TB.Builder: 146 132 132 143
• State TB.Builder (modify): 81 83
• State TB.Builder (modify'): 83 79
• Writer [Text]: 189
• Writer (DList Text): 121 122 122
• Writer Html with runReader: 106 100

Pretty interesting. IORef wins out of them all, so unfortunately no obvious improvement to be gained by playing with that.