My solution to Jamis Buck's Weekly Programming Challenge #7
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Weekly Programming Challenge #7

Jamis Buck publishes programming challenges on his blog at This is my submission for week 7. This time it's all about B+trees. I managed to (almost) complete normal mode, which includes

  • A basic B+ tree with configurable arity (children per node).
  • The insertion algorithm, allowing you to add a new key/value pair to the tree.
  • The search algorithm, allowing you to find the value for a named key.

I also included Configurable key and value data types from the list of Hard Mode.

The project is created using Holy Project ( which is a project generator for Haskell using Cabal.

Build, run and test

There is no executable, only the package and unit tests


cabal build


cabal test


The tree consists of the type (Ord key) => BplusTree key value with one type parameter for keys and one for values. The available construcors are

    Node {
      arity :: Int
      , keys :: [key]
      , children :: [BplusTree key value]
      , sibling :: (Maybe (BplusTree key value))


    Leaf {
       arity :: Int
       , keyValues :: [(key, value)]
       , sibling :: (Maybe (BplusTree key value))

Each constructor takes the arity of the tree. This is needed when creating the root node. Later this is handled by the insert function.

Insert a mapping from key 4 to value '4' in an empty tree with an arity of 3, like this: insert 4 '4' (createEmptyRoot 3)

Finding a Leaf that contains the mapping for a key like this: searchNode 4 tree where tree is a BplusTree.