Add tasks for all the new languages

Task/Constrained-genericity/Morfa/constrained-genericity-1.morfa

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+import morfa.type.traits;
+
+template < T >
+alias IsEdible = HasMember< T, "eat" >;
+
+template < T >
+if (IsEdible< T >)
+struct FoodBox
+{
+    var food: T[];
+}
+
+struct Carrot
+{
+    func eat(): void {}
+}
+
+struct Car {}
+
+func main(): void
+{
+    var carrotBox: FoodBox< Carrot >;   // OK
+    carrotBox.food ~= Carrot();        // Adds a carrot
+
+    // var carBox: FoodBox< Car >;      // Not allowed
+    static assert( not trait(compiles, func() { var carBox: FoodBox< Car >; } ));
+}

Task/Constrained-genericity/Morfa/constrained-genericity-2.morfa

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+interface IEdible
+{
+    public func eat(): void;
+}
+
+template < T >
+if (IsDerivedOf< T, IEdible >)
+struct FoodBox
+{
+    var food: T[];
+}
+
+class Carrot: IEdible
+{
+    public override func eat(): void {}
+}
+
+class Car {}
+
+func main(): void
+{
+    var carrotBox: FoodBox< Carrot >;   // OK
+
+    // var carBox: FoodBox< Car >;      // Not allowed
+    static assert( not trait(compiles, func() { var carBox: FoodBox< Car >; } ));
+}

Task/Constrained-genericity/Nim/constrained-genericity.nim

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+type
+  Eatable = generic e
+    eat(e)
+
+  FoodBox[e: Eatable] = seq[e]
+
+  Food = object
+    name: string
+    count: int
+
+proc eat(x: int) = echo "Eating the int: ", x
+proc eat(x: Food) = echo "Eating ", x.count, " ", x.name, "s"
+
+var ints = FoodBox[int](@[1,2,3,4,5])
+var fs = FoodBox[Food](@[])
+
+fs.add Food(name: "Hamburger", count: 3)
+fs.add Food(name: "Cheeseburger", count: 5)
+
+for f in fs:
+  eat(f)

Task/Constrained-genericity/Sidef/constrained-genericity.sidef

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+class FoodBox(*food { .all { .respond_to(:eat) } }) { }
+
+class Fruit { method eat { ... } }
+class Apple < Fruit {  }
+
+say FoodBox(Fruit(), Apple()).dump  #=> FoodBox(food: [Fruit(), Apple()])
+say FoodBox(Apple(), "foo")         #!> ERROR: class `FoodBox` !~ (Apple, String)

Task/Constrained-genericity/Swift/constrained-genericity-1.swift

@@ -0,0 +1,3 @@
+protocol Eatable {
+    func eat()
+}

Task/Constrained-genericity/Swift/constrained-genericity-2.swift

@@ -0,0 +1,3 @@
+struct FoodBox<T: Eatable> {
+    var food: [T]
+}

Task/Constrained-genericity/Swift/constrained-genericity-3.swift

@@ -0,0 +1,2 @@
+func foo<T: Eatable>(x: T) { }
+// although in this case this is no more useful than just "func foo(x: Eatable)"