hw-koans

Course for learn functional programming.

Prerequisites

• cabal-3.0.0.0 or above
• ghc-8.6.5 or above

Running

Run:

$ git clone [email protected]:haskell-works/hw-koans.git
$ cd hw-koans
$ cabal v2-test --enable-tests --test-show-details=direct
...
15 modules not enrolled
All enrolled 0 test modules succeeded
Test suite koan-test: PASS
...

The above output shows that there are 15 modules not enrolled. This course is structure into modules, which are found under the koan/Koan directory.

Each module defines the following a function:

enrolled :: Bool
enrolled = False

You will need to enable the module by changing enrolled to True then running the test command again:

$ cabal v2-test --enable-tests --test-show-details=direct
━━━ Check.Functor ━━━
  ✗ prop_fmap_void failed at test/Check/Functor.hs:43:3
    after 1 test and 1 shrink.

       ┏━━ test/Check/Functor.hs ━━━
    40 ┃ prop_fmap_void :: Property
    41 ┃ prop_fmap_void = property $ do
    42 ┃   mb <- forAll $ Gen.maybe (Gen.int Range.constantBounded)
       ┃   │ Nothing
    43 ┃   K.void mb === P.void mb
       ┃   ^^^^^^^^^^^^^^^^^^^^^^^
       ┃   │ ━━━ Exception (ErrorCall) ━━━
       ┃   │ TODO: implement void
       ┃   │ CallStack (from HasCallStack):
       ┃   │   error, called at koan/Koan/Functor.hs:34:8 in hw-koans-0.1.0.0-inplace:Koan.Functor

    This failure can be reproduced by running:
    > recheck (Size 0) (Seed 16511336219962586096 11754670307026383675) prop_fmap_void
...

From the above you can see the failure TODO: implement void in the module koan/Koan/Functor.hs file at line 34.

Go to that location to find the function void and implement it by replacing error "TODO: implement void" with a correct implementation:

void :: Functor f => f a -> f ()
void = error "TODO: implement void"

Run the test command to check that you've correctly implemented the function then repeat for the other failures until there are no more errors.

IDE support

The project will build & test in Visual Studio Code with ⌘⇧V.

List of modules

The following are modules in order of difficulty.

Introductory

• Koan.Start
• Koan.List
• Koan.Eq
• Koan.Ord
• Koan.Simple

Beginner

• Koan.Functor
• Koan.Maybe
• Koan.Applicative
• Koan.Monad
• Koan.State

Acknowledgements

This course was inspired by the Data 61 Functional Programming Course