Abstraction in Shake

shake.hs

main = do
  let buildDir = "_build"
      -- how to express on a non-string level that everything should only ever be put into "_build"?
      -- how to never repeat that information anywhere else, much less do problematic string operations
      -- with the `"_build"` constant?
      staticDir = "static"
      staticFiles = map (staticDir <>) [ "foo" "bar" "baz" ]
      
  (buildDir </> staticDir </> "*") %> \outFile ->
    -- we only get `out`, which is some unknown string
    -- so: how to recover the semantic information where to find the static file?
    let inFile = magicallyAndManuallyStriptheBuildDirAgain outFile
    copyFile inFile outFile
    
  -- another thing:
  -- No separation between build inputs and mutated files
  phony "clean, maybe?" $ do
    removeFiles "foo"
    -- oops, of course should have been `buildDir </> "foo"`.
    -- ah, well, who needed those source files anyway.