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module Main where

import Lib

main :: IO ()
main = return ()

module Lib
  (
  )
where

data Box a = Box a deriving (Show)

wrap :: a -> Box a
wrap = Box

unwrap :: Box a -> a
unwrap (Box x) = x

% stack ghci
Using main module: 1. Package `lesson' component lesson:exe:lesson-exe with main-is file: /Users/…/lesson/app/Main.hs
lesson> initial-build-steps (lib + exe)
The following GHC options are incompatible with GHCi and have not been passed to it: -threaded
Configuring GHCi with the following packages: lesson

* * * * * * * *

Warning: Multiple files use the same module name:
         * Paths_lesson found at the following paths
           * /Users/…/lesson/.stack-work/dist/x86_64-osx/Cabal-3.4.1.0/build/autogen/Paths_lesson.hs (lesson:lib)
           * /Users/…/lesson/.stack-work/dist/x86_64-osx/Cabal-3.4.1.0/build/lesson-exe/autogen/Paths_lesson.hs (lesson:exe:lesson-exe)
* * * * * * * *

GHCi, version 9.0.2: https://www.haskell.org/ghc/  :? for help
macro 'doc' overwrites builtin command.  Use ':def!' to overwrite.
(0.00 secs, 0 bytes)
(0.00 secs, 0 bytes)
Loaded GHCi configuration from /Users/…/.ghc/ghci.conf
[1 of 3] Compiling Lib              ( /Users/…/lesson/src/Lib.hs, interpreted )
[2 of 3] Compiling Main             ( /Users/…/lesson/app/Main.hs, interpreted )
[3 of 3] Compiling Paths_lesson     ( /Users/…/lesson/.stack-work/dist/x86_64-osx/Cabal-3.4.1.0/build/autogen/Paths_lesson.hs, interpreted )
Ok, three modules loaded.
Loaded GHCi configuration from /private/var/folders/wj/52wjq8dn0fj1qltsnx3xxpnh0000gn/T/haskell-stack-ghci/ac09a814/ghci-script
*Main Lib Paths_lesson
λ> :load Lib
[1 of 1] Compiling Lib              ( /Users/…/lesson/src/Lib.hs, interpreted )
Ok, one module loaded.
(0.01 secs,)
*Lib
λ> wrap $ Box 'a'
Box (Box 'a')
it :: Box (Box Char)
(0.01 secs, 512,432 bytes)
*Lib
λ> :t wrap $ Box 'a'
wrap $ Box 'a' :: Box (Box Char)
*Lib
λ> :quit 
Leaving GHCi.
%