langs a-z

Task/Function-composition/Objective-C/function-composition-2.m

@@ -0,0 +1,42 @@
+#include <Foundation/Foundation.h>
+
+typedef id (^Function)(id);
+
+// a commodity for "encapsulating" double f(double)
+typedef double (*func_t)(double);
+Function encapsulate(func_t f) {
+  return [[^(id x) { return [NSNumber numberWithDouble: f([x doubleValue])]; } copy] autorelease];
+}
+
+Function compose(Function a, Function b) {
+  return [[^(id x) { return a(b(x)); } copy] autorelease];
+}
+
+// functions outside...
+double my_f(double x)
+{
+  return x+1.0;
+}
+
+double my_g(double x)
+{
+  return x*x;
+}
+
+
+int main()
+{
+  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
+
+  Function f = encapsulate(my_f);
+  Function g = encapsulate(my_g);
+
+  Function composed = compose(f, g);
+
+  printf("g(2.0) = %lf\n", [g([NSNumber numberWithDouble: 2.0]) doubleValue]);
+  printf("f(2.0) = %lf\n", [f([NSNumber numberWithDouble: 2.0]) doubleValue]);
+  printf("f(g(2.0)) = %lf\n", [composed([NSNumber numberWithDouble: 2.0]) doubleValue]);
+
+  [pool release];
+  return 0;
+}