Adding dependencies to stack project

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• Haskell cross-platform getChar with NoBuffering

  Haskell has a bug in Windows that seems fixed with WinIO in GHC9: getChar ignores NoBuffering mode - it does not evaluate until Enter is pressed.

  Somebody suggested a workaround via a foreign call:

  {-# LANGUAGE ForeignFunctionInterface #-}
  import Data.Char
  import Foreign.C.Types
  getHiddenChar = fmap (chr.fromEnum) c_getch
  foreign import ccall unsafe "conio.h getch"
    c_getch :: IO CInt
  

  It kind of works, but the problem is that it seems to block the output to console until some key is pressed, and I am concurrently reading key presses and writing to console from different threads.

  Could you please help find a way (e.g. write a foreign function call - I do not know much about it, unfortunately) to read characters/keys from console, without buffering and echo, and without blocking output to console, in GHC 8.8.x (or at least 8.10.x), on Windows?

  Thank you!

  (Ideally I need a cross-platform way, but I can do it via conditional compilation, so if it only works on Windows it is ok. Above foreign call is not cross-platform already).
• What is the difference between install, v1-install, v2-install and new-install?

  The commands install, v1-install, v2-install and new-install are simply described to "Install packages" when running man cabal. Are they different from one another? Which is the preferred option?
• iterate and garbage collection in Haskell

  I have a question about how the GHC implements a simple code. A question of performance and also technical.

  This is a simple example from John Hughes' "Why Functional Programming Matters" article. The square root calculation.

  To do the calculation we need the previous approximation and we can use the iterate function that creates a list with approximations:

  [a0, f(a0), f(f(a0), ...] and so on

  And then with within it will stop when it is convenient:

  within eps (a:b:xs) = if abs(a-b) < eps then b else within eps (b:xs)
  

  The question is how is this performed in constant space?

  Does the GC know in the recursive call, within eps (b: xs) that head a of the list is no longer in scope and then it is collected?

  If this is the case, then at each iteration, would the GHC always create and then destroy a location in memory (variable)? And how can this perform as well as in a procedural language where the variable is always reused?
• how to use a my own Haskell library in a stack project?

  I have a Haskell library I wrote that I compile with stack. I now need to use it in another Haskell stack project. In order to do that, I have added its current version to the extra_deps of my new project's stack.yaml and listed it among the build_depends of one its executables. When I run stack build, however, it obviously tries to download the library from the internet. How do I specify that the library is local and where to find it?

  Thanks in advance!
• How to import files from the test folder in a Haskell-Stack project?

  I'm using stack and my Haskell project has the standard shape:

  .
  ├── app
  │   └── Main.hs
  ├── LICENSE
  ├── README.md
  ├── Setup.hs
  ├── src
  │   ├── Lib.hs
  │   └── ...
  ├── stack.yaml
  ├── package.yaml
  ├── test
  │   └── Suit1.hs
  │   └── Suit2.hs
  │   └── TestUtility.hs
  └── MyProject.cabal
  

  I have two test suits Suit1 and Suit2 whcih share a common code in TestUtility. However I'm failing to import this common code!

  import TestUtility

  Fails with Could not find module ‘TestUtility’. Looking at the verbose output of GHC, I can tell that it's only looking at the src and app folders for modules. How do I tell it to look at the test folder?

  In my package.yaml I'm using the following:

  tests:
   suite1:
      main:                Suite1.hs
      source-dirs:         test
      ghc-options:         
      - -threaded
      - -rtsopts
      - -with-rtsopts=-N
      - -main-is Suite1
      other-modules:
      - TestUtility.hs ## Doesn't seem to be doing anything
      dependencies:
      - acme-missiles
  

  So my main question is, what do I need to add so that GHC sees other files in the test directory but only for test suits (don't want to export that in the library)?

  Secondary question, is why is GHC lookin in the app folder? Is that default behavior, or is is derived from where the executables are?