延迟求值和无穷(4)

template< typename Record>  
void print_rec(Record* r){ 
        if(r){ 
                std::cout<< r->value<<”, ”; 
                print_rec(r->next()); 
        } 
        else 
                std::cout<<” n”; 
} 
 
int main(int, char**){ 
        record* r1= new record(90, new record(250, new record(1000, 0))); 
        record* r2=transform(r1, discount); 
        record* r3=filter(r2, Greator<double>(500.0)); 
        print_rec(r3); 
        delete r3; 
        delete r2; 
        delete r1; 
 
        stream_record* r4= new stream_record(90, new stream_record(250, new stream_record(1000, 0))); 
        stream_record* r5=transform(r4, discount); 
        stream_record* r6=filter(r5, Greator<double>(500.0)); 
        print_rec(r6); 
        delete r6; 
        delete r5; 
        delete r4; 
}

template< typename Record>  
double getAt(Record* r, int i){ 
        if(i==0)  
                return (r!=0)? r->value : -1; 
        else 
                return getAt(r->next(), i-1); 
}

stream_record* r5=transform(r4, discount); 
std::cout<<”transform overn”; 
std::cout<<”1st:  ”<<getAt(r5, 0)<<”n”; 
std::cout<<”1st gotn”; 
std::cout<<”2nd:  ”<<getAt(r5, 1)<<”n”; 
std::cout<<”2nd gotn”; 
std::cout<<”3rd:  ”<<getAt(r5, 2)<<”n”;