tasks a-s

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
+}