haskell annoyances

• ghc has buggy warnings:
  • view patterns: Warning: Pattern match(es) are non-exhaustive
  • qualified imports: Warning: Module `Ui' is imported, but nothing from it is used
  Fixed in 6.12! Yay!
• hacks and workarounds:
  • tools/unline_hack HPC doesn't work with {-# LINE ... #-}
  • tools/hscdeps.py hsc2hs doesn't have a way to emit hsc → .h deps
  • hsc2hs still emits {-# INCLUDE ... #-} which now causes warnings
  • haddock broken for 6.12
• lack of stack traces:
  • Pass caller explicitly:

            track_to_generic note (track_id, scale_id, events) = do
                let name = "LPitch.track_to_generic"
                scale <- Cmd.get_scale name scale_id
                base <- maybe
                    (Cmd.throw $ name ++ ": unknown base note: " ++ show note)
                    return (Pitch.scale_note_to_generic scale note)
            

  • Keep "stack" in Reader environment:

     Derive.with_msg 

  • ugly preprocessor hacks to get line number
• crummy update syntax

      track_views <- modify_at "set_track_width"
          (Block.view_tracks view) tracknum $ \tview →
              tview { Block.track_view_width = width }
      update_view view_id (view { Block.view_tracks = track_views })
  
      update_view view_id view = modify $ \st → st
          { state_views = Map.adjust (const view) view_id (state_views st) }
  
      modify_at :: (UiStateMonad m) => String → [a] → Int → (a → a) → m [a]
      modify_at msg xs i f = case post of
          [] → throw $ msg ++ ": can't replace index " ++ show i
              ++ " of list with length " ++ show (length xs)
          (elt:rest) → return (pre ++ f elt : rest)
          where (pre, post) = splitAt i xs
      

  vs.

   state.get_view(view_id).tracks[tracknum].width = width 

  Functional references might help.
• haddock is fussy
  • all files must typecheck
  • crummy errors (e.g. syntax error in comment with no line number)
• debugging is a pain
  • ghci debugger is mysterious
  • trace only works when you use the variable
  • lack of stack traces!
• lack of introspection makes tests harder to write, e.g. python
  • self.assertEqual(result, [(StringLike("regex"), 42)])
  • Equal(result, some_big_data) can say where the data differs
• ghc compiles slowly, ld links slowly