A-M baby

Task/Function-composition/C/function-composition.c

@@ -0,0 +1,64 @@
+#include <stdlib.h>
+
+/* generic interface for functors from double to double */
+typedef struct double_to_double {
+  double (*fn)(struct double_to_double *, double);
+} double_to_double;
+
+#define CALL(f, x) f->fn(f, x)
+
+
+/* functor returned by compose */
+typedef struct compose_functor {
+  double (*fn)(struct compose_functor *, double);
+  double_to_double *f;
+  double_to_double *g;
+} compose_functor;
+/* function to be used in "fn" in preceding functor */
+double compose_call(compose_functor *this, double x) {
+  return CALL(this->f, CALL(this->g, x));
+}
+/* returns functor that is the composition of functors
+   f & g. caller is responsible for deallocating memory */
+double_to_double *compose(double_to_double *f,
+                          double_to_double *g) {
+  compose_functor *result = malloc(sizeof(compose_functor));
+  result->fn = &compose_call;
+  result->f = f;
+  result->g = g;
+  return (double_to_double *)result;
+}
+
+
+
+#include <math.h>
+
+/* we can make functors for sin and asin by using
+   the following as "fn" in a functor */
+double sin_call(double_to_double *this, double x) {
+  return sin(x);
+}
+double asin_call(double_to_double *this, double x) {
+  return asin(x);
+}
+
+
+
+#include <stdio.h>
+
+int main() {
+  double_to_double *my_sin = malloc(sizeof(double_to_double));
+  my_sin->fn = &sin_call;
+  double_to_double *my_asin = malloc(sizeof(double_to_double));
+  my_asin->fn = &asin_call;
+
+  double_to_double *sin_asin = compose(my_sin, my_asin);
+
+  printf("%f\n", CALL(sin_asin, 0.5)); /* prints "0.500000" */
+
+  free(sin_asin);
+  free(my_sin);
+  free(my_asin);
+
+  return 0;
+}