Parametric polymorphism: Difference between revisions

<lang nim>import strutils, sugar

type Tree[T] = ref object

left, right: Tree[T]

proc newTree[T](value = default(T)): Tree[T] =

## Create a tree with a single node with the given value.

Tree[T](value: value)

proc map[T, U](tree: Tree[T]; f: (T) -> U): Tree[U] =

## Apply function "f" to each element of a tree, building

## another tree.

result = newTree[U](f(tree.value))

if not tree.left.isNil:

result.left = tree.left.map(f)

if not tree.right.isNil:

result.right = tree.right.map(f)

proc print(tree: Tree; indent = 0) =

## Print a tree.

let start = repeat(' ', indent)

echo start, "value: ", tree.value

if tree.left.isNil:

echo start, " nil"

else:

print(tree.left, indent + 2)

if tree.right.isNil:

echo start, " nil"

else:

print(tree.right, indent + 2)

when isMainModule:

echo "Initial tree:"

var tree = newTree[int](5)

tree.left = newTree[int](2)

tree.right = newTree[int](7)

print(tree)

echo ""

echo "Tree created by applying a function to each node:"

let tree1 = tree.map((x) => 1 / x)

print(tree1)</lang>

{{out}}

<pre>Initial tree:

value: 5

value: 2

nil

nil

value: 7

nil

nil

Tree created by applying a function to each node:

value: 0.2

value: 0.5

nil

nil

value: 0.1428571428571428

nil

nil</pre>