Data commit

Task/Parametric-polymorphism/00-META.yaml

@@ -0,0 +1,5 @@
+---
+category:
+- Type System
+from: http://rosettacode.org/wiki/Parametric_polymorphism
+note: Basic language learning

Task/Parametric-polymorphism/00-TASK.txt

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+[[wp:Parametric Polymorphism|Parametric Polymorphism]] is a way to define types or functions that are generic over other types. The genericity can be expressed by using ''type variables'' for the parameter type, and by a mechanism to explicitly or implicitly replace the type variables with concrete types when necessary.
+
+
+;Task:
+Write a small example for a type declaration that is parametric over another type, together with a short bit of code (and its type signature) that uses it. 
+
+
+A good example is a container type, let's say a binary tree, together with some function that traverses the tree, say, a ''map''-function that operates on every element of the tree.
+
+This language feature only applies to statically-typed languages.
+<br><br>
+

Task/Parametric-polymorphism/Ada/parametric-polymorphism-1.ada

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+generic
+   type Element_Type is private;
+package Container is
+   type Tree is tagged private;
+   procedure Replace_All(The_Tree : in out Tree; New_Value : Element_Type);
+private
+   type Node;
+   type Node_Access is access Node;
+   type Tree tagged record
+      Value : Element_type;
+      Left  : Node_Access := null;
+      Right : Node_Access := null;
+   end record;
+end Container;

Task/Parametric-polymorphism/Ada/parametric-polymorphism-2.ada

@@ -0,0 +1,12 @@
+package body Container is
+   procedure Replace_All(The_Tree : in out Tree; New_Value : Element_Type) is
+   begin
+      The_Tree.Value := New_Value;
+      If The_Tree.Left /= null then
+         The_Tree.Left.all.Replace_All(New_Value);
+      end if;
+      if The_tree.Right /= null then
+         The_Tree.Right.all.Replace_All(New_Value);
+      end if;
+   end Replace_All;
+end Container;

Task/Parametric-polymorphism/C++/parametric-polymorphism-1.cpp

@@ -0,0 +1,9 @@
+template<class T>
+class tree
+{
+  T value;
+  tree *left;
+  tree *right;
+public:
+  void replace_all (T new_value);
+};

Task/Parametric-polymorphism/C++/parametric-polymorphism-2.cpp

@@ -0,0 +1,9 @@
+template<class T>
+void tree<T>::replace_all (T new_value)
+{
+  value = new_value;
+  if (left != NULL)
+    left->replace_all (new_value);
+  if (right != NULL)
+    right->replace_all (new_value);
+}

Task/Parametric-polymorphism/C-sharp/parametric-polymorphism-1.cs

@@ -0,0 +1,27 @@
+using System;
+
+class BinaryTree<T>
+{
+    public T value;
+    public BinaryTree<T> left;
+    public BinaryTree<T> right;
+
+    public BinaryTree(T value)
+    {
+        this.value = value;
+    }
+
+    public BinaryTree<U> Map<U>(Func<T, U> f)
+    {
+        BinaryTree<U> tree = new BinaryTree<U>(f(this.value));
+        if (this.left != null)
+        {
+            tree.left = this.left.Map(f);
+        }
+        if (this.right != null)
+        {
+            tree.right = this.right.Map(f);
+        }
+        return tree;
+    }
+}

Task/Parametric-polymorphism/C-sharp/parametric-polymorphism-2.cs

@@ -0,0 +1,11 @@
+class Program
+{
+    static void Main(string[] args)
+    {
+        BinaryTree<int> b = new BinaryTree<int>(6);
+        b.left = new BinaryTree<int>(5);
+        b.right = new BinaryTree<int>(7);
+
+        BinaryTree<double> b2 = b.Map(x => x * 0.5);
+    }
+}

Task/Parametric-polymorphism/C-sharp/parametric-polymorphism-3.cs

@@ -0,0 +1,48 @@
+using System;
+
+class BinaryTree<T>
+{
+    public BinaryTree<T> Left { get; }
+    public BinaryTree<T> Right { get; }
+    public T Value { get; }
+
+    public BinaryTree(T value, BinaryTree<T> left = null, BinaryTree<T> right = null)
+    {
+        this.Value = value;
+        this.Left = left;
+        this.Right = right;
+    }
+
+    public BinaryTree<U> Map<U>(Func<T, U> f)
+    {
+        return new BinaryTree<U>(f(this.Value), this.Left?.Map(f), this.Right?.Map(f));
+    }
+
+    public override string ToString()
+    {
+        var sb = new System.Text.StringBuilder();
+        this.ToString(sb, 0);
+        return sb.ToString();
+    }
+
+    private void ToString(System.Text.StringBuilder sb, int depth)
+    {
+        sb.Append(new string('\t', depth));
+        sb.AppendLine(this.Value?.ToString());
+        this.Left?.ToString(sb, depth + 1);
+        this.Right?.ToString(sb, depth + 1);
+    }
+}
+
+static class Program
+{
+    static void Main()
+    {
+        var b = new BinaryTree<int>(6, new BinaryTree<int>(5), new BinaryTree<int>(7));
+
+        BinaryTree<double> b2 = b.Map(x => x * 0.5);
+
+        Console.WriteLine(b);
+        Console.WriteLine(b2);
+    }
+}

Task/Parametric-polymorphism/C/parametric-polymorphism.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+#define decl_tree_type(T)                                                       \
+        typedef struct node_##T##_t node_##T##_t, *node_##T;                    \
+        struct node_##T##_t { node_##T left, right; T value; };                 \
+                                                                                \
+        node_##T node_##T##_new(T v) {                                          \
+                node_##T node = malloc(sizeof(node_##T##_t));                   \
+                node->value = v;                                                \
+                node->left = node->right = 0;                                   \
+                return node;                                                    \
+        }                                                                       \
+        node_##T node_##T##_insert(node_##T root, T v) {                        \
+                node_##T n = node_##T##_new(v);                                 \
+                while (root) {                                                  \
+                        if (root->value < n->value)                             \
+                                if (!root->left) return root->left = n;         \
+                                else root = root->left;                         \
+                        else                                                    \
+                                if (!root->right) return root->right = n;       \
+                                else root = root->right;                        \
+                }                                                               \
+                return 0;                                                       \
+        }
+
+#define tree_node(T) node_##T
+#define node_insert(T, r, x) node_##T##_insert(r, x)
+#define node_new(T, x) node_##T##_new(x)
+
+decl_tree_type(double);
+decl_tree_type(int);
+
+int main()
+{
+        int i;
+        tree_node(double) root_d = node_new(double, (double)rand() / RAND_MAX);
+
+        for (i = 0; i < 10000; i++)
+                node_insert(double, root_d, (double)rand() / RAND_MAX);
+
+        tree_node(int) root_i = node_new(int, rand());
+        for (i = 0; i < 10000; i++)
+                node_insert(int, root_i, rand());
+
+        return 0;
+}

Task/Parametric-polymorphism/C3/parametric-polymorphism-1.c3

@@ -0,0 +1,15 @@
+module tree<Type>;
+
+struct Tree
+{
+    Type value;
+    Tree* left;
+    Tree* right;
+}
+
+fn void Tree.replaceAll(Tree* a_tree, Type new_value)
+{
+    a_tree.value = new_value;
+    if (a_tree.left) a_tree.left.replaceAll(new_value);
+    if (a_tree.right) a_tree.right.replaceAll(new_value);
+}

Task/Parametric-polymorphism/C3/parametric-polymorphism-2.c3

@@ -0,0 +1,7 @@
+define IntTree = tree<int>::Tree;
+
+fn void test()
+{
+    IntTree inttree;
+    inttree.replaceAll(3);
+}

Task/Parametric-polymorphism/Ceylon/parametric-polymorphism.ceylon

@@ -0,0 +1,31 @@
+class BinaryTree<Data>(shared Data data, shared BinaryTree<Data>? left = null, shared BinaryTree<Data>? right = null) {
+	
+	shared BinaryTree<NewData> myMap<NewData>(NewData f(Data d)) =>
+			BinaryTree {
+				data = f(data);
+				left = left?.myMap(f);
+				right = right?.myMap(f);
+			};
+}
+
+shared void run() {
+	
+	value tree1 = BinaryTree {
+		data = 3;
+		left = BinaryTree {
+			data = 4;
+		};
+		right = BinaryTree {
+			data = 5;
+			left = BinaryTree {
+				data = 6;
+			};
+		};
+	};
+	
+	tree1.myMap(print);
+	print("");
+	
+	value tree2 = tree1.myMap((x) => x * 333.33);
+	tree2.myMap(print);
+}

Task/Parametric-polymorphism/Clean/parametric-polymorphism-1.clean

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+::Tree a = Empty | Node a (Tree a) (Tree a)
+
+mapTree :: (a -> b) (Tree a) -> (Tree b)
+mapTree f Empty        = Empty
+mapTree f (Node x l r) = Node (f x) (mapTree f l) (mapTree f r)

Task/Parametric-polymorphism/Clean/parametric-polymorphism-2.clean

@@ -0,0 +1,3 @@
+instance Functor Tree where
+    fmap f Empty        = Empty
+    fmap f (Node x l r) = Node (f x) (fmap f l) (fmap f r)

Task/Parametric-polymorphism/Clean/parametric-polymorphism-3.clean

@@ -0,0 +1,2 @@
+add1Everywhere :: (f a) -> (f a) | Functor f & Num a
+add1Everywhere nums = fmap (\x = x + 1) nums

Task/Parametric-polymorphism/Common-Lisp/parametric-polymorphism.lisp

@@ -0,0 +1,2 @@
+(deftype pair (&key (car 't) (cdr 't))
+  `(cons ,car ,cdr))

Task/Parametric-polymorphism/D/parametric-polymorphism.d

@@ -0,0 +1,46 @@
+class ArrayTree(T, uint N) {
+    T[N] data;
+    typeof(this) left, right;
+
+    this(T initValue) { this.data[] = initValue; }
+
+    void tmap(const void delegate(ref typeof(data)) dg) {
+        dg(this.data);
+        if (left) left.tmap(dg);
+        if (right) right.tmap(dg);
+    }
+}
+
+void main() { // Demo code.
+    import std.stdio;
+
+    // Instantiate the template ArrayTree of three doubles.
+    alias AT3 = ArrayTree!(double, 3);
+
+    // Allocate the tree root.
+    auto root = new AT3(1.00);
+
+    // Add some nodes.
+    root.left = new AT3(1.10);
+    root.left.left = new AT3(1.11);
+    root.left.right = new AT3(1.12);
+
+    root.right = new AT3(1.20);
+    root.right.left = new AT3(1.21);
+    root.right.right = new AT3(1.22);
+
+    // Now the tree has seven nodes.
+
+    // Show the arrays of the whole tree.
+    //root.tmap(x => writefln("%(%.2f %)", x));
+    root.tmap((ref x) => writefln("%(%.2f %)", x));
+
+    // Modify the arrays of the whole tree.
+    //root.tmap((x){ x[] += 10; });
+    root.tmap((ref x){ x[] += 10; });
+
+    // Show the arrays of the whole tree again.
+    writeln();
+    //root.tmap(x => writefln("%(%.2f %)", x));
+    root.tmap((ref x) => writefln("%(%.2f %)", x));
+}

Task/Parametric-polymorphism/Dart/parametric-polymorphism.dart

@@ -0,0 +1,42 @@
+class TreeNode<T> {
+
+  T value;
+  TreeNode<T> left;
+  TreeNode<T> right;
+
+  TreeNode(this.value);
+
+  TreeNode map(T f(T t)) {
+    var node = new TreeNode(f(value));
+    if(left != null) {
+      node.left = left.map(f);
+    }
+    if(right != null) {
+      node.right = right.map(f);
+    }
+    return node;
+  }
+
+  void forEach(void f(T t)) {
+    f(value);
+    if(left != null) {
+      left.forEach(f);
+    }
+    if(right != null) {
+      right.forEach(f);
+    }
+  }
+}
+
+void main() {
+  TreeNode root = new TreeNode(1);
+  root.left = new TreeNode(2);
+  root.right = new TreeNode(3);
+  root.left.right = new TreeNode(4);
+
+  print('first tree');
+  root.forEach(print);
+  var newRoot = root.map((t) => t * 222);
+  print('second tree');
+  newRoot.forEach(print);
+}

Task/Parametric-polymorphism/E/parametric-polymorphism-1.e

@@ -0,0 +1,31 @@
+interface TreeAny guards TreeStamp {}
+def Tree {
+    to get(Value) {
+        def Tree1 {
+            to coerce(specimen, ejector) {
+                def tree := TreeAny.coerce(specimen, ejector)
+                if (tree.valueType() != Value) {
+                    throw.eject(ejector, "Tree value type mismatch")
+                }
+                return tree
+            }
+        }
+        return Tree1
+    }
+}
+
+def makeTree(T, var value :T, left :nullOk[Tree[T]], right :nullOk[Tree[T]]) {
+    def tree implements TreeStamp {
+        to valueType() { return T }
+        to map(f) {
+            value := f(value)  # the declaration of value causes this to be checked
+            if (left != null) {
+                left.map(f)
+            }
+            if (right != null) {
+                right.map(f)
+            }
+        }
+    }
+    return tree
+}

Task/Parametric-polymorphism/E/parametric-polymorphism-2.e

@@ -0,0 +1,11 @@
+? def t := makeTree(int, 0, null, null)
+# value: <tree>
+
+? t :Tree[String]
+# problem: Tree value type mismatch
+
+? t :Tree[Int]
+# problem: Failed: Undefined variable: Int
+
+? t :Tree[int]
+# value: <tree>

Task/Parametric-polymorphism/F-Sharp/parametric-polymorphism-1.fs

@@ -0,0 +1,9 @@
+    namespace RosettaCode
+
+    type BinaryTree<'T> =
+      | Element of 'T
+      | Tree of 'T * BinaryTree<'T> * BinaryTree<'T>
+      member this.Map(f) =
+        match this with
+        | Element(x) -> Element(f x)
+        | Tree(x,left,right) -> Tree((f x), left.Map(f), right.Map(f))

Task/Parametric-polymorphism/F-Sharp/parametric-polymorphism-2.fs

@@ -0,0 +1,2 @@
+    let t1 = Tree(2, Element(1), Tree(4,Element(3),Element(5)) )
+    let t2 = t1.Map(fun x -> x * 10)

Task/Parametric-polymorphism/Fortran/parametric-polymorphism-1.f

@@ -0,0 +1,35 @@
+      MODULE SORTSEARCH		!Genuflect towards Prof. D. Knuth.
+
+       INTERFACE FIND			!Binary chop search, not indexed.
+        MODULE PROCEDURE
+     1   FINDI4,				!I: of integers.
+     2   FINDF4,FINDF8,				!F: of numbers.
+     3          FINDTTI2,FINDTTI4		!T: of texts.
+       END INTERFACE FIND
+
+      CONTAINS
+      INTEGER FUNCTION FINDI4(THIS,NUMB,N)	!Binary chopper. Find i such that THIS = NUMB(i)
+       USE ASSISTANCE		!Only for the trace stuff.
+       INTENT(IN) THIS,NUMB,N	!Imply read-only, but definitely no need for any "copy-back".
+       INTEGER*4 THIS,NUMB(1:*)	!Where is THIS in array NUMB(1:N)?
+       INTEGER N		!The count. In other versions, it is supplied by the index.
+       INTEGER L,R,P		!Fingers.
+Chop away.
+        L = 0			!Establish outer bounds.
+        R = N + 1		!One before, and one after, the first and last.
+    1   P = (R - L)/2		!Probe point offset. Beware integer overflow with (L + R)/2.
+        IF (P.LE.0) THEN	!Aha! Nowhere! And THIS follows NUMB(L).
+          FINDI4 = -L		!Having -L rather than 0 (or other code) might be of interest.
+          RETURN		!Finished.
+        END IF			!So much for exhaustion.
+        P = P + L		!Convert from offset to probe point.
+        IF (THIS - NUMB(P)) 3,4,2	!Compare to the probe point.
+    2   L = P			!Shift the left bound up: THIS follows NUMB(P).
+        GO TO 1			!Another chop.
+    3   R = P			!Shift the right bound down: THIS precedes NUMB(P).
+        GO TO 1			!Try again.
+Caught it! THIS = NUMB(P)
+    4   FINDI4 = P		!So, THIS is found, here!
+      END FUNCTION FINDI4	!On success, THIS = NUMB(FINDI4); no fancy index here...
+
+      END MODULE SORTSEARCH

Task/Parametric-polymorphism/Fortran/parametric-polymorphism-2.f

@@ -0,0 +1,6 @@
+      TYPE STUFF
+       INTEGER CODE       !A key number.
+       CHARACTER*6 NAME   !Associated data.
+       INTEGER THIS       !etc.
+      END TYPE STUFF
+      TYPE(STUFF) TABLE(600)   !An array of such entries.

Task/Parametric-polymorphism/Go/parametric-polymorphism-1.go

@@ -0,0 +1,53 @@
+package main
+
+import "fmt"
+
+func average(c intCollection) float64 {
+    var sum, count int
+    c.mapElements(func(n int) {
+        sum += n
+        count++
+    })
+    return float64(sum) / float64(count)
+}
+
+func main() {
+    t1 := new(binaryTree)
+    t2 := new(bTree)
+    a1 := average(t1)
+    a2 := average(t2)
+    fmt.Println("binary tree average:", a1)
+    fmt.Println("b-tree average:", a2)
+}
+
+type intCollection interface {
+    mapElements(func(int))
+}
+
+type binaryTree struct {
+    // dummy representation details
+    left, right bool
+}
+
+func (t *binaryTree) mapElements(visit func(int)) {
+    // dummy implementation
+    if t.left == t.right {
+        visit(3)
+        visit(1)
+        visit(4)
+    }
+}
+
+type bTree struct {
+    // dummy representation details
+    buckets int
+}
+
+func (t *bTree) mapElements(visit func(int)) {
+    // dummy implementation
+    if t.buckets >= 0 {
+        visit(1)
+        visit(5)
+        visit(9)
+    }
+}

Task/Parametric-polymorphism/Go/parametric-polymorphism-2.go

@@ -0,0 +1,13 @@
+package rosettacode
+
+type Tree(type T) struct {
+    val T
+    left *Tree(T)
+    right *Tree(T)
+}
+
+func (t *Tree(T)) ReplaceAll(rep T) {
+    t.val = rep
+    if t.left != nil  { t.left.ReplaceAll(rep) }
+    if t.right != nil { t.right.ReplaceAll(rep) }
+}

Task/Parametric-polymorphism/Groovy/parametric-polymorphism.groovy

@@ -0,0 +1,17 @@
+class Tree<T> {
+    T value
+    Tree<T> left
+    Tree<T> right
+
+    Tree(T value = null, Tree<T> left = null, Tree<T> right = null) {
+        this.value = value
+        this.left = left
+        this.right = right
+    }
+
+    void replaceAll(T value) {
+        this.value = value
+        left?.replaceAll(value)
+        right?.replaceAll(value)
+    }
+}

Task/Parametric-polymorphism/Haskell/parametric-polymorphism-1.hs

@@ -0,0 +1,5 @@
+data Tree a = Empty | Node a (Tree a) (Tree a)
+
+mapTree :: (a -> b) -> Tree a -> Tree b
+mapTree f Empty        = Empty
+mapTree f (Node x l r) = Node (f x) (mapTree f l) (mapTree f r)

Task/Parametric-polymorphism/Haskell/parametric-polymorphism-2.hs

@@ -0,0 +1,3 @@
+instance Functor Tree where
+    fmap f Empty        = Empty
+    fmap f (Node x l r) = Node (f x) (fmap f l) (fmap f r)

Task/Parametric-polymorphism/Haskell/parametric-polymorphism-3.hs

@@ -0,0 +1,2 @@
+add1Everywhere :: (Functor f, Num a) => f a -> f a
+add1Everywhere nums = fmap (\x -> x + 1) nums

Task/Parametric-polymorphism/Icon/parametric-polymorphism.icon

@@ -0,0 +1,10 @@
+procedure main()
+    bTree := [1, [2, [4, [7]], [5]], [3, [6, [8], [9]]]]
+    mapTree(bTree, write)
+    bTree := [1, ["two", ["four", [7]], [5]], [3, ["six", ["eight"], [9]]]]
+    mapTree(bTree, write)
+end
+
+procedure mapTree(tree, f)
+    every f(\tree[1]) | mapTree(!tree[2:0], f)
+end

Task/Parametric-polymorphism/Inform-7/parametric-polymorphism-1.inf

@@ -0,0 +1,13 @@
+Polymorphism is a room.
+
+To find (V - K) in (L - list of values of kind K):
+	repeat with N running from 1 to the number of entries in L:
+		if entry N in L is V:
+			say "Found [V] at entry [N] in [L].";
+			stop;
+	say "Did not find [V] in [L]."
+
+When play begins:
+	find "needle" in {"parrot", "needle", "rutabaga"};
+	find 6 in {2, 3, 4};
+	end the story.

Task/Parametric-polymorphism/Inform-7/parametric-polymorphism-2.inf

@@ -0,0 +1,8 @@
+list of numbers
+relation of texts to rooms
+object based rulebook producing a number
+description of things
+activity on things
+number valued property
+text valued table column
+phrase (text, text) -> number

Task/Parametric-polymorphism/Java/parametric-polymorphism.java

@@ -0,0 +1,13 @@
+public class Tree<T>{
+	private T value;
+	private Tree<T> left;
+	private Tree<T> right;
+
+	public void replaceAll(T value){
+		this.value = value;
+		if (left != null)
+			left.replaceAll(value);
+		if (right != null)
+			right.replaceAll(value);
+	}
+}

Task/Parametric-polymorphism/Julia/parametric-polymorphism.julia

@@ -0,0 +1,46 @@
+module BinaryTrees
+
+mutable struct BinaryTree{V}
+    v::V
+    l::Union{BinaryTree{V}, Nothing}
+    r::Union{BinaryTree{V}, Nothing}
+end
+
+BinaryTree(v) = BinaryTree(v, nothing, nothing)
+
+map(f, bt::BinaryTree) = BinaryTree(f(bt.v), map(f, bt.l), map(f, bt.r))
+map(f, bt::Nothing) = nothing
+
+let inttree = BinaryTree(
+        0,
+        BinaryTree(
+            1,
+            BinaryTree(3),
+            BinaryTree(5),
+        ),
+        BinaryTree(
+            2,
+            BinaryTree(4),
+            nothing,
+        ),
+    )
+    map(x -> 2x^2, inttree)
+end
+
+let strtree = BinaryTree(
+        "hello",
+        BinaryTree(
+            "world!",
+            BinaryTree("Julia"),
+            nothing,
+        ),
+        BinaryTree(
+            "foo",
+            BinaryTree("bar"),
+            BinaryTree("baz"),
+        ),
+    )
+    map(uppercase, strtree)
+end
+
+end

Task/Parametric-polymorphism/Kotlin/parametric-polymorphism.kotlin

@@ -0,0 +1,24 @@
+// version 1.0.6
+
+class BinaryTree<T>(var value: T) {
+    var left : BinaryTree<T>? = null
+    var right: BinaryTree<T>? = null
+
+    fun <U> map(f: (T) -> U): BinaryTree<U> {
+        val tree = BinaryTree<U>(f(value))
+        if (left  != null) tree.left  = left?.map(f)
+        if (right != null) tree.right = right?.map(f)
+        return tree
+    }
+
+    fun showTopThree() = "(${left?.value}, $value, ${right?.value})"
+}
+
+fun main(args: Array<String>) {
+    val b   = BinaryTree(6)
+    b.left  = BinaryTree(5)
+    b.right = BinaryTree(7)
+    println(b.showTopThree())
+    val b2  = b.map { it * 10.0 }
+    println(b2.showTopThree())
+}

Task/Parametric-polymorphism/Mathematica/parametric-polymorphism.math

@@ -0,0 +1,10 @@
+f[a_] := Join[a, a]
+f[{1, 2, 3}]
+f[{"1", "2", "3"}]
+f[{1.1, 2.1, 3.1}]
+f[G[1, "a", Pi]]
+g[x_] := x^2
+g[2]
+g[3.5]
+g[Pi]
+g["a"]

Task/Parametric-polymorphism/Mercury/parametric-polymorphism.mercury

@@ -0,0 +1,6 @@
+:- type tree(A) ---> empty ; node(A, tree(A), tree(A)).
+
+:- func map(func(A) = B, tree(A)) = tree(B).
+
+map(_, empty) = empty.
+map(F, node(A, Left, Right)) = node(F(A), map(F, Left), map(F, Right)).

Task/Parametric-polymorphism/Nim/parametric-polymorphism.nim

@@ -0,0 +1,48 @@
+import strutils, sugar
+
+type Tree[T] = ref object
+  value: T
+  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)

Task/Parametric-polymorphism/OCaml/parametric-polymorphism.ocaml

@@ -0,0 +1,6 @@
+type 'a tree = Empty | Node of 'a * 'a tree * 'a tree
+
+(** val map_tree : ('a -> 'b) -> 'a tree -> 'b tree *)
+let rec map_tree f = function
+  | Empty        -> Empty
+  | Node (x,l,r) -> Node (f x, map_tree f l, map_tree f r)

Task/Parametric-polymorphism/Objective-C/parametric-polymorphism.m

@@ -0,0 +1,16 @@
+@interface Tree<T> : NSObject {
+  T value;
+  Tree<T> *left;
+  Tree<T> *right;
+}
+
+- (void)replaceAll:(T)v;
+@end
+
+@implementation Tree
+- (void)replaceAll:(id)v {
+  value = v;
+  [left replaceAll:v];
+  [right replaceAll:v];
+}
+@end

Task/Parametric-polymorphism/Phix/parametric-polymorphism-1.phix

@@ -0,0 +1,3 @@
+(phixonline)-->
+ <span style="color: #0000FF;">?</span><span style="color: #7060A8;">sort</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">shuffle</span><span style="color: #0000FF;">({</span><span style="color: #000000;">5</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"oranges"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">6</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"apples"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">7</span><span style="color: #0000FF;">}))</span>
+<!--

Task/Parametric-polymorphism/Phix/parametric-polymorphism-2.phix

@@ -0,0 +1,45 @@
+(phixonline)-->
+ <span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
+ <span style="color: #008080;">enum</span> <span style="color: #000000;">data</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">left</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">right</span>
+
+ <span style="color: #008080;">function</span> <span style="color: #000000;">tmap</span><span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span> <span style="color: #000000;">tree</span><span style="color: #0000FF;">,</span> <span style="color: #004080;">integer</span> <span style="color: #000000;">rid</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">data</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">rid</span><span style="color: #0000FF;">(</span><span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">data</span><span style="color: #0000FF;">])</span>
+     <span style="color: #008080;">if</span> <span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">]!=</span><span style="color: #004600;">null</span> <span style="color: #008080;">then</span> <span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">tmap</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">deep_copy</span><span style="color: #0000FF;">(</span><span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">],</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span><span style="color: #000000;">rid</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
+     <span style="color: #008080;">if</span> <span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">]!=</span><span style="color: #004600;">null</span> <span style="color: #008080;">then</span> <span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">tmap</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">deep_copy</span><span style="color: #0000FF;">(</span><span style="color: #000000;">tree</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">],</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span><span style="color: #000000;">rid</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
+     <span style="color: #008080;">return</span> <span style="color: #000000;">tree</span>
+ <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
+
+ <span style="color: #008080;">function</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #004080;">object</span> <span style="color: #000000;">v</span><span style="color: #0000FF;">)</span>
+     <span style="color: #008080;">return</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">v</span><span style="color: #0000FF;">,</span><span style="color: #004600;">null</span><span style="color: #0000FF;">,</span><span style="color: #004600;">null</span><span style="color: #0000FF;">}</span>
+ <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
+
+ <span style="color: #008080;">function</span> <span style="color: #000000;">add10</span><span style="color: #0000FF;">(</span><span style="color: #004080;">atom</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">return</span> <span style="color: #000000;">x</span><span style="color: #0000FF;">+</span><span style="color: #000000;">10</span> <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
+
+ <span style="color: #008080;">procedure</span> <span style="color: #000000;">main</span><span style="color: #0000FF;">()</span>
+     <span style="color: #004080;">object</span> <span style="color: #000000;">root</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.00</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000080;font-style:italic;">-- Add some nodes.</span>
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.10</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">][</span><span style="color: #000000;">left</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.11</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">left</span><span style="color: #0000FF;">][</span><span style="color: #000000;">right</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.12</span><span style="color: #0000FF;">)</span>
+
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.20</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">][</span><span style="color: #000000;">left</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.21</span><span style="color: #0000FF;">)</span>
+     <span style="color: #000000;">root</span><span style="color: #0000FF;">[</span><span style="color: #000000;">right</span><span style="color: #0000FF;">][</span><span style="color: #000000;">right</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">newnode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1.22</span><span style="color: #0000FF;">)</span>
+
+     <span style="color: #000080;font-style:italic;">-- Now the tree has seven nodes.
+
+     -- Show the whole tree.</span>
+     <span style="color: #7060A8;">ppOpt</span><span style="color: #0000FF;">({</span><span style="color: #004600;">pp_Nest</span><span style="color: #0000FF;">,</span><span style="color: #000000;">2</span><span style="color: #0000FF;">})</span>
+     <span style="color: #7060A8;">pp</span><span style="color: #0000FF;">(</span><span style="color: #000000;">root</span><span style="color: #0000FF;">)</span>
+
+     <span style="color: #000080;font-style:italic;">-- Modify the whole tree.</span>
+     <span style="color: #000000;">root</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">tmap</span><span style="color: #0000FF;">(</span><span style="color: #000000;">root</span><span style="color: #0000FF;">,</span><span style="color: #000000;">add10</span><span style="color: #0000FF;">)</span>
+
+     <span style="color: #000080;font-style:italic;">-- Create a whole new tree.</span>
+     <span style="color: #004080;">object</span> <span style="color: #000000;">root2</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">tmap</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">deep_copy</span><span style="color: #0000FF;">(</span><span style="color: #000000;">root</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">),</span><span style="color: #000000;">newnode</span><span style="color: #0000FF;">)</span>
+
+     <span style="color: #000080;font-style:italic;">-- Show the whole tree again.</span>
+     <span style="color: #7060A8;">pp</span><span style="color: #0000FF;">(</span><span style="color: #000000;">root</span><span style="color: #0000FF;">)</span>
+ <span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
+ <span style="color: #000000;">main</span><span style="color: #0000FF;">()</span>
+<!--

Task/Parametric-polymorphism/PicoLisp/parametric-polymorphism.l

@@ -0,0 +1,4 @@
+(de mapTree (Tree Fun)
+   (set Tree (Fun (car Tree)))
+   (and (cadr Tree) (mapTree @ Fun))
+   (and (cddr Tree) (mapTree @ Fun)) )

Task/Parametric-polymorphism/REXX/parametric-polymorphism.rexx

@@ -0,0 +1,32 @@
+/*REXX program  demonstrates  (with displays)  a method of   parametric polymorphism.   */
+call newRoot  1.00, 3                            /*new root,  and also indicate 3 stems.*/
+                                                 /* [↓]  no need to label the stems.    */
+call addStem  1.10                               /*a new stem  and  its initial value.  */
+call addStem  1.11                               /*"  "    "    "    "     "      "     */
+call addStem  1.12                               /*"  "    "    "    "     "      "     */
+call addStem  1.20                               /*"  "    "    "    "     "      "     */
+call addStem  1.21                               /*"  "    "    "    "     "      "     */
+call addStem  1.22                               /*"  "    "    "    "     "      "     */
+                       call sayNodes             /*display some nicely formatted values.*/
+call modRoot  50                                 /*modRoot will add fifty to all stems. */
+                       call sayNodes             /*display some nicely formatted values.*/
+exit                                             /*stick a fork in it,  we're all done. */
+/*──────────────────────────────────────────────────────────────────────────────────────*/
+addStem:  nodes= nodes + 1;   do j=1  for stems;   root.nodes.j= arg(1);   end;     return
+newRoot:  parse arg @,stems; nodes= -1; call addStem copies('═',9); call addStem @; return
+/*──────────────────────────────────────────────────────────────────────────────────────*/
+modRoot:  arg #;  do    j=1  for nodes           /*traipse through all the defined nodes*/
+                     do k=1  for stems           /*add bias ──►───────────────────────┐ */
+                     if datatype(root.j.k, 'N')  then root.j.k= root.j.k + #   /* ◄───┘ */
+                     end   /*k*/                 /* [↑]  add  if  stem value is numeric.*/
+                  end      /*j*/
+          return
+/*──────────────────────────────────────────────────────────────────────────────────────*/
+sayNodes: w= 9;   do    j=0  to  nodes;  _=      /*ensure each of the nodes gets shown. */
+                     do k=1  for stems;  _= _ center(root.j.k, w)  /*concatenate a node.*/
+                     end   /*k*/
+                  $= word('node='j,  1 + (j<1) ) /*define a label for this line's output*/
+                  say center($, w)  substr(_, 2) /*ignore 1st (leading) blank which was */
+                  end      /*j*/                 /* [↑]         caused by concatenation.*/
+          say                                    /*show a blank line to separate outputs*/
+          return

Task/Parametric-polymorphism/Racket/parametric-polymorphism.rkt

@@ -0,0 +1,20 @@
+#lang typed/racket
+
+(define-type (Tree A) (U False (Node A)))
+
+(struct: (A) Node
+  ([val : A] [left : (Tree A)] [right : (Tree A)])
+  #:transparent)
+
+(: tree-map (All (A B) (A -> B) (Tree A) -> (Tree B)))
+(define (tree-map f tree)
+  (match tree
+    [#f #f]
+    [(Node val left right)
+     (Node (f val) (tree-map f left) (tree-map f right))]))
+
+;; unit tests
+(require typed/rackunit)
+(check-equal?
+ (tree-map add1 (Node 5 (Node 3 #f #f) #f))
+ (Node 6 (Node 4 #f #f) #f))

Task/Parametric-polymorphism/Raku/parametric-polymorphism.raku

@@ -0,0 +1,20 @@
+role BinaryTree[::T] {
+    has T $.value;
+    has BinaryTree[T] $.left;
+    has BinaryTree[T] $.right;
+
+    method replace-all(T $value) {
+        $!value = $value;
+        $!left.replace-all($value) if $!left.defined;
+        $!right.replace-all($value) if $!right.defined;
+    }
+}
+
+class IntTree does BinaryTree[Int] { }
+
+my IntTree $it .= new(value => 1,
+                      left  => IntTree.new(value => 2),
+                      right => IntTree.new(value => 3));
+
+$it.replace-all(42);
+say $it;

Task/Parametric-polymorphism/Rust/parametric-polymorphism.rust

@@ -0,0 +1,46 @@
+struct TreeNode<T> {
+    value: T,
+    left: Option<Box<TreeNode<T>>>,
+    right: Option<Box<TreeNode<T>>>,
+}
+
+impl <T> TreeNode<T> {
+    fn my_map<U,F>(&self, f: &F) -> TreeNode<U> where
+            F: Fn(&T) -> U {
+        TreeNode {
+            value: f(&self.value),
+            left: match self.left {
+                None => None,
+                Some(ref n) => Some(Box::new(n.my_map(f))),
+            },
+            right: match self.right {
+                None => None,
+                Some(ref n) => Some(Box::new(n.my_map(f))),
+            },
+        }
+    }
+}
+
+fn main() {
+    let root = TreeNode {
+        value: 3,
+        left: Some(Box::new(TreeNode {
+            value: 55,
+            left: None,
+            right: None,
+        })),
+        right: Some(Box::new(TreeNode {
+            value: 234,
+            left: Some(Box::new(TreeNode {
+                value: 0,
+                left: None,
+                right: None,
+            })),
+            right: None,
+        })),
+    };
+    root.my_map(&|x| { println!("{}" , x)});
+    println!("---------------");
+    let new_root = root.my_map(&|x| *x as f64 * 333.333f64);
+    new_root.my_map(&|x| { println!("{}" , x) });
+}

Task/Parametric-polymorphism/Scala/parametric-polymorphism-1.scala

@@ -0,0 +1,4 @@
+case class Tree[+A](value: A, left: Option[Tree[A]], right: Option[Tree[A]]) {
+  def map[B](f: A => B): Tree[B] =
+    Tree(f(value), left map (_.map(f)), right map (_.map(f)))
+}

Task/Parametric-polymorphism/Scala/parametric-polymorphism-2.scala

@@ -0,0 +1,5 @@
+class Employee(val name: String)
+class Manager(name: String) extends Employee(name)
+
+val t = Tree(new Manager("PHB"), None, None)
+val t2: Tree[Employee] = t

Task/Parametric-polymorphism/Scala/parametric-polymorphism-3.scala

@@ -0,0 +1,2 @@
+def toName(e: Employee) = e.name
+val treeOfNames = t.map(toName)

Task/Parametric-polymorphism/Scala/parametric-polymorphism-4.scala

@@ -0,0 +1 @@
+trait Function1[-T1, +R]

Task/Parametric-polymorphism/Scala/parametric-polymorphism-5.scala

@@ -0,0 +1,6 @@
+case class Tree[+A](value: A, left: Option[Tree[A]], right: Option[Tree[A]]) {
+  def map[B](f: A => B): Tree[B] =
+    Tree(f(value), left map (_.map(f)), right map (_.map(f)))
+  def find[B >: A](what: B): Boolean =
+    (value == what) || left.map(_.find(what)).getOrElse(false) || right.map(_.find(what)).getOrElse(false)
+}

Task/Parametric-polymorphism/Scala/parametric-polymorphism-6.scala

@@ -0,0 +1,2 @@
+if (t2.find(new Employee("Dilbert")))
+  println("Call Catbert!")

Task/Parametric-polymorphism/Scala/parametric-polymorphism-7.scala

@@ -0,0 +1,4 @@
+trait DFA {
+  type Element
+  val map = new collection.mutable.HashMap[Element, DFA]()
+}

Task/Parametric-polymorphism/Seed7/parametric-polymorphism.seed7

@@ -0,0 +1,37 @@
+$ include "seed7_05.s7i";
+
+const func type: container (in type: elemType) is func
+  result
+    var type: container is void;
+  begin
+    container := array elemType;
+
+    global
+
+      const func container: map (in container: aContainer,
+          inout elemType: aVariable, ref func elemType: aFunc) is func
+        result
+          var container: mapResult is container.value;
+        begin
+          for aVariable range aContainer do
+            mapResult &:= aFunc;
+          end for;
+        end func;
+
+    end global;
+  end func;
+
+const type: intContainer is container(integer);
+var intContainer: container1 is [] (1, 2, 4, 6, 10, 12, 16, 18, 22);
+var intContainer: container2 is 0 times 0;
+
+const proc: main is func
+  local
+    var integer: num is 0;
+  begin
+    container2 := map(container1, num, num + 1);
+    for num range container2 do
+      write(num <& " ");
+    end for;
+    writeln;
+  end func;

Task/Parametric-polymorphism/Standard-ML/parametric-polymorphism.ml

@@ -0,0 +1,5 @@
+datatype 'a tree = Empty | Node of 'a * 'a tree * 'a tree
+
+(** val map_tree = fn : ('a -> 'b) -> 'a tree -> 'b tree *)
+fun map_tree f Empty = Empty
+  | map_tree f (Node (x,l,r)) = Node (f x, map_tree f l, map_tree f r)

Task/Parametric-polymorphism/Swift/parametric-polymorphism-1.swift

@@ -0,0 +1,11 @@
+class Tree<T> {
+  var value: T?
+  var left: Tree<T>?
+  var right: Tree<T>?
+
+  func replaceAll(value: T?) {
+    self.value = value
+    left?.replaceAll(value)
+    right?.replaceAll(value)
+  }
+}

Task/Parametric-polymorphism/Swift/parametric-polymorphism-2.swift

@@ -0,0 +1,11 @@
+enum Tree<T> {
+  case Empty
+  indirect case Node(T, Tree<T>, Tree<T>)
+
+  func map<U>(f : T -> U) -> Tree<U> {
+    switch(self) {
+    case     .Empty        : return .Empty
+    case let .Node(x, l, r): return .Node(f(x), l.map(f), r.map(f))
+    }
+  }
+}

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-1.ursala

@@ -0,0 +1 @@
+binary_tree_of "node-type" = "node-type"%hhhhWZAZ

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-2.ursala

@@ -0,0 +1,5 @@
+#import tag
+
+#fix general_type_fixer 1
+
+binary_tree_of "node-type" = ("node-type",(binary_tree_of "node-type")%Z)%drWZwlwAZ

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-3.ursala

@@ -0,0 +1 @@
+binary_tree_of = %-hhhhWZAZ

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-4.ursala

@@ -0,0 +1 @@
+binary_tree_map "f" = ~&a^& ^A/"f"@an ~&amPfamPWB

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-5.ursala

@@ -0,0 +1 @@
+binary_tree_map = ~&a^&+ ^A\~&amPfamPWB+ @an

Task/Parametric-polymorphism/Ursala/parametric-polymorphism-6.ursala

@@ -0,0 +1,7 @@
+string_tree = binary_tree_of %s
+
+x = 'foo': ('bar': (),'baz': ())
+
+#cast string_tree
+
+example = (binary_tree_map "s". "s"--"s") x

Task/Parametric-polymorphism/Visual-Basic-.NET/parametric-polymorphism.vb

@@ -0,0 +1,38 @@
+Class BinaryTree(Of T)
+    ReadOnly Property Left As BinaryTree(Of T)
+    ReadOnly Property Right As BinaryTree(Of T)
+    ReadOnly Property Value As T
+
+    Sub New(value As T, Optional left As BinaryTree(Of T) = Nothing, Optional right As BinaryTree(Of T) = Nothing)
+        Me.Value = value
+        Me.Left = left
+        Me.Right = right
+    End Sub
+
+    Function Map(Of U)(f As Func(Of T, U)) As BinaryTree(Of U)
+        Return New BinaryTree(Of U)(f(Me.Value), Me.Left?.Map(f), Me.Right?.Map(f))
+    End Function
+
+    Overrides Function ToString() As String
+        Dim sb As New Text.StringBuilder()
+        Me.ToString(sb, 0)
+        Return sb.ToString()
+    End Function
+
+    Private Overloads Sub ToString(sb As Text.StringBuilder, depth As Integer)
+        sb.Append(New String(ChrW(AscW(vbTab)), depth))
+        sb.AppendLine(Me.Value?.ToString())
+        Me.Left?.ToString(sb, depth + 1)
+        Me.Right?.ToString(sb, depth + 1)
+    End Sub
+End Class
+
+Module Program
+    Sub Main()
+        Dim b As New BinaryTree(Of Integer)(6, New BinaryTree(Of Integer)(5), New BinaryTree(Of Integer)(7))
+        Dim b2 As BinaryTree(Of Double) = b.Map(Function(x) x * 0.5)
+
+        Console.WriteLine(b)
+        Console.WriteLine(b2)
+    End Sub
+End Module

Task/Parametric-polymorphism/Visual-Prolog/parametric-polymorphism.pro

@@ -0,0 +1,19 @@
+domains
+   tree{Type} = branch(tree{Type} Left, tree{Type} Right); leaf(Type Value).
+
+class predicates
+   treewalk : (tree{X},function{X,Y}) -> tree{Y} procedure (i,i).
+
+clauses
+   treewalk(branch(Left,Right),Func) = branch(NewLeft,NewRight) :-
+        NewLeft = treewalk(Left,Func), NewRight = treewalk(Right,Func).
+
+   treewalk(leaf(Value),Func) = leaf(X) :-
+        X = Func(Value).
+
+   run():-
+       init(),
+       X = branch(leaf(2), branch(leaf(3),leaf(4))),
+       Y = treewalk(X,addone),
+       write(Y),
+       succeed().

Task/Parametric-polymorphism/Wren/parametric-polymorphism.wren

@@ -0,0 +1,53 @@
+class BinaryTree {
+    construct new(T, value) {
+        if (!(T is Class)) Fiber.abort ("T must be a class.")
+        if (value.type != T) Fiber.abort("Value must be of type T.")
+        _kind = T
+        _value = value
+        _left = null
+        _right = null
+    }
+
+    // constructor overload to enable kind to be inferred from type of value
+    static new (value) { new(value.type, value) }
+
+    kind  { _kind }
+    value { _value}
+    value=(v) {
+        if (v.type != _kind) Fiber.abort("Value must be of type %(_kind)")
+        _value = v
+    }
+
+    left  { _left }
+    right { _right }
+    left=(b) {
+        if (b.type != BinaryTree || b.kind != _kind) {
+            Fiber.abort("Argument must be a BinaryTree of type %(_kind)")
+        }
+        _left = b
+    }
+    right=(b) {
+        if (b.type != BinaryTree || b.kind != _kind) {
+            Fiber.abort("Argument must be a BinaryTree of type %(_kind)")
+        }
+        _right = b
+    }
+
+    map(f) {
+        var tree = BinaryTree.new(f.call(_value))
+        if (_left) tree.left = left.map(f)
+        if (_right) tree.right = right.map(f)
+        return tree
+    }
+
+    showTopThree() { "(%(left.value), %(value), %(right.value))" }
+}
+
+var b    = BinaryTree.new(6)
+b.left   = BinaryTree.new(5)
+b.right  = BinaryTree.new(7)
+System.print(b.showTopThree())
+
+var b2   = b.map{ |i| i * 10 }
+System.print(b2.showTopThree())
+b2.value = "six" // generates an error because "six" is not a Num