Weeder

The principle is to delete dead code (pulling up the weeds). To do that, run:

• GHC with -fwarn-unused-binds -fwarn-unused-imports, which finds unused definitions and unused imports.
• HLint, looking for "Redundant extension" hints, which finds unused extensions.
• This tool, weeder . which detects redundant build-depends in the .cabal and functions that are exported internally but not available outside this library.

To use weeder your code must be building with stack, as it piggy-backs off some files stack generates. If you don't normally build with stack a simple stack init && weeder . --build is likely to be sufficient.