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