benjamin-thomas/programming-in-haskell

Reading the book: Programming in Haskell, by Graham Hutton

Basic commands

• cabal clean
• cabal build
• cabal run (launches ./app/Main.hs)
• cabal repl

  • Chapter01.hello

Possible workflows

Simple

cabal repl
ghci> hello
Hello from lib!
ghci> Chapter01.double 2
4
ghci> import Chapter01
ghci> double 2
5 -- bad result
ghci> :reload -- after code change. NOTE :r is an available shortcut
ghci> double 2
4 -- fixed!

# KISS: reload the module and re-run "double 2" by pressing <Up><Enter>
ghci> :cmd return $ unlines [":reload", "double 2"]
Ok, four modules loaded.
4

Not sure why I would use this, keeping for ref.

cabal exec ghci src/Chapter01.hs
ghci> hello
"World!"
ghci> Chapter01.double 2
4

Ghcid workflow

# verbose
ghcid --command "cabal repl" --test "Chapter01.double 2"
# short
ghcid -c "cabal repl" -T "Chapter01.double 2"

 # Needs to be in sync with the current ghc, that's a bit of a pain.
cabal install doctest --overwrite-policy=always
doctest --version;ghc --version

# Run all the test examples and exit with a summary.
cabal repl --with-ghc=doctest
cabal exec doctest src/

# Re-run all the doctests on any file change
find ./src/ | entr -rc cabal exec doctest src/

# Re-run chapter-specific doctests on any file change -- BETTER!
ghcid --command 'cabal new-repl' --test ':!doctest ./src/Chapter01.hs'

Run tests

ghcid -c 'cabal repl' -T ':!doctest ./src/Chapter01.hs'
ghcid -c 'cabal repl' -T ':!doctest ./src/'

Pretty printing in GHCi

cabal repl --build-depends pretty-simple
# or
stack ghci --package pretty-simple ./myFile.hs

Then:

*Main> :m Text.Pretty.Simple
Prelude Text.Pretty.Simple> pPrint [1,2,3]
[ 1
, 2
, 3
]
Prelude Text.Pretty.Simple> pPrintOpt CheckColorTty defaultOutputOptionsDarkBg { outputOptionsCompact = True } [1,2,3]
[ 1, 2, 3 ]

*Main Text.Pretty.Simple> :load TicTacToe.hs

-- WARNING: does not play well with laziness (favor `pPrint` in that case)
*Main Text.Pretty.Simple> let pPrint' = pPrintOpt CheckColorTty defaultOutputOptionsDarkBg { outputOptionsCompact = True }

*Main Text.Pretty.Simple> mapM_ pPrint' (moves empty O)
[ [ O, B, B ], [ B, B, B ], [ B, B, B ] ]
[ [ B, O, B ], [ B, B, B ], [ B, B, B ] ]
[ [ B, B, O ], [ B, B, B ], [ B, B, B ] ]
[ [ B, B, B ], [ O, B, B ], [ B, B, B ] ]
[ [ B, B, B ], [ B, O, B ], [ B, B, B ] ]
[ [ B, B, B ], [ B, B, O ], [ B, B, B ] ]
[ [ B, B, B ], [ B, B, B ], [ O, B, B ] ]
[ [ B, B, B ], [ B, B, B ], [ B, O, B ] ]
[ [ B, B, B ], [ B, B, B ], [ B, B, O ] ]

Tips

To test unexported functions in ghci make sure to run:

:m *Chapter13.Lesson

not:

:m Chapter13.Lesson