sicp-ex-3.55

  
  
 (define (partial-sums s) 
   (cons-stream (stream-car s) 
                (add-streams (stream-cdr s) (partial-sums s)))) 

  
  
 (define (partial-sums s) 
   (add-streams s (cons-stream 0 (partial-sums s)))) 
  

@huntzhan: nice, very elegant

Must have self-reference to avoid recalculation:

  
 (define (partial-sums s) 
   (define ps (add-streams s (cons-stream 0 ps))) 
   ps) 
  

My solution:

  
 (define (partial-sums S) 
   (cons-stream (stream-car S) 
                (add-streams (partial-sums (stream-cdr S)) 
                             S))) 

dekuofa1995's solution is wrong. For his, (partial-sums integers) returns 1, 3, 7, 12... correct solution should return (partial-sums integers) => 1, 3, 6, 10...

 (define (partial-sums s) 
   (cons-stream (stream-car s) 
                (add-streams (partial-sums s) 
                             (stream-cdr s))))