Initial data commit

Task/Y-combinator/C/y-combinator.c

@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/* func: our one and only data type; it holds either a pointer to
+   a function call, or an integer.  Also carry a func pointer to
+   a potential parameter, to simulate closure                   */
+typedef struct func_t *func;
+typedef struct func_t {
+        func (*fn) (func, func);
+        func _;
+        int num;
+} func_t;
+
+func new(func(*f)(func, func), func _) {
+        func x = malloc(sizeof(func_t));
+        x->fn = f;
+        x->_ = _;       /* closure, sort of */
+        x->num = 0;
+        return x;
+}
+
+func call(func f, func n) {
+        return f->fn(f, n);
+}
+
+func Y(func(*f)(func, func)) {
+        func g = new(f, 0);
+        g->_ = g;
+        return g;
+}
+
+func num(int n) {
+        func x = new(0, 0);
+        x->num = n;
+        return x;
+}
+
+
+func fac(func self, func n) {
+        int nn = n->num;
+        return nn > 1   ? num(nn * call(self->_, num(nn - 1))->num)
+                        : num(1);
+}
+
+func fib(func self, func n) {
+        int nn = n->num;
+        return nn > 1
+                ? num(  call(self->_, num(nn - 1))->num +
+                        call(self->_, num(nn - 2))->num )
+                : num(1);
+}
+
+void show(func n) { printf(" %d", n->num); }
+
+int main() {
+        int i;
+        func f = Y(fac);
+        printf("fac: ");
+        for (i = 1; i < 10; i++)
+                show( call(f, num(i)) );
+        printf("\n");
+
+        f = Y(fib);
+        printf("fib: ");
+        for (i = 1; i < 10; i++)
+                show( call(f, num(i)) );
+        printf("\n");
+
+        return 0;
+}