Zora.TreeGraphing

A typeclass with default implementation for graphing trees with Haskell GraphViz. It is intended to be extremely straightforward to graph your data type; you only need to define three very simple functions (example implementations below).

Documentation

class TreeGraphable g where

A typeclass for algebraic data types that are able to be graphed.

For these descriptions, assume the following example data type:

 data Tree a = Empty | Leaf a | Node a (Tree a) (Tree a)

Being an instance of TreeGraphable is enough to make your data type an instance of Zoldable; just define

 instance Zoldable Tree where
 	zoldMap :: (Monoid m) => (Tree a -> m) -> Tree a -> m
 	zoldMap = G.zoldMap

Methods

value :: g a -> a

Gets the value contained in a node. For example,

 value (Empty) = error "Empty nodes don't contain values."
 value (Leaf x) = x
 value (Node x _ _) = x

get_children :: g a -> [g a]

Gets the children of the current node. For example,

 get_children (Empty) = error "Empty nodes don't have children."
 get_children (Leaf _) = []
 get_children (Node _ l r) = [l, r]

is_empty :: g a -> Bool

Returns whether a node is empty. Sometimes, when declaring algebraic data types, it is desirable to have an "Empty" value constructor. If your data type does not have an "Empty" value constructor, just always return False.

 is_empty Empty = True
 is_empty _ = False

zoldMap :: Monoid m => (g a -> m) -> g a -> m

A default implementation of zoldMap. This enough to make you an instance of Zoldable (in Zora.Types). You shouldn't need to override this implementation.

graph :: (Show a, Ord a) => g a -> IO String

Graphs the given TreeGraphable data type. Creates and writes to a file named "graph.png", overwriting any existing files with that name. You won't need to override this implementation.