We decided we wanted to ramp up the team's functional programming skills. To this end, we committed to working through Brent Yorgey's CIS 194 lecture series on Haskell. This is a 12 week course and there are homework assignments for each week.
Our goal is to work through a week of the course's content every Friday afternoon. Our first session will be on Friday the 20th of July, 2018.
Jump into the #fp channel in the Stacktrace slack to chat about the course, or any FP concepts in general.
-
Install the Nix package manager
-
Run the following
$ nix-shell --command 'cabal configure --enable-tests && cabal test'
- To run ghci
$ nix-shell --command ghci
From now on you can type nix-shell and be put into a bash shell which has ghc, ghci, cabal, ghcid, hlint, and hindent. For more info on using Nix ask in #dotfiles.
-
Install the Haskell Platform. This includes the ghc compiler, ghci repl, and cabal build tool.
-
Run the following
$ cabal configure
$ cabal install cabal-install
$ cabal install --only-dependencies --enable-tests
$ cabal configure --enable-tests
$ cabal test
- To run ghci
$ ghci
You'll be spending a lot of time in ghci, which is a Read, Eval, Print, Loop (aka 'repl'). Once you enter ghci you can run commands, which are prefixed with ':'. Entering :help will print a list of available commands.
The most helpful of these are likely to be :info and :type.
:info or :i for short will tell you everything GHCI can about an expression.
> :i Maybe
data Maybe a = Nothing | Just a -- Defined in ‘GHC.Base’
instance Applicative Maybe -- Defined in ‘GHC.Base’
... MORE
> :i (+)
class Num a where
(+) :: a -> a -> a
...
-- Defined in ‘GHC.Num’
infixl 6 +
:type or :t for short will tell you the type of an expression.
> :t Just
Just :: a -> Maybe a
> :t (+)
(+) :: Num a => a -> a -> a
Each week we'll be adding a set of hspec specs in a ./test/Week<N>/ directory. We'll also add some files in ./src/Week<N>/ to serve as a starting point for your implementations. To run only the tests for a given week you can use GHCI. Below is an example of running only the credit card tests for week one.
$ ghci test/Week01/CreditCardValidatorSpec.hs
GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /Users/bradparker/code/cosmos/training/CIS194/.ghci
Ok, two modules loaded.
> hspec spec
CreditCardValidator
toDigits
converts positive Integers to a list of digits FAILED [1]
toDigitsRev
does what toDigits does in reverse FAILED [2]
doubleEveryOther
doubles every second digit starting from the second last FAILED [3]
sumDigits
sums the sum of the digits of all numbers in a list FAILED [4]
validate
indicates whether an Integer could be a valid credit card number FAILED [5]
Failures:
... error details and more!
You can also run dev/watch to get a file-watching test-re-running setup going with the help of GHCID.
To run only the tests for a given spec file using the watch script (defaults to all specs):
$ dev/watch test/Week01/CreditCardValidatorSpec.hs