Scheme functions

filters.scm

(define filters
  (lambda ((pred <function>) (stream <stream>))
    (cond ((stream-empty? stream) stream)
          ((pred (stream-first stream))
           (stream-cons (stream-first stream)
                        (filters pred (stream-rest stream))))
          (else (filters pred (stream-rest stream))))))

maps.scm

; maps thorugh stream
(define maps
  (lambda ((f <function>) (stream <stream>))
    (if (stream-empty? stream) 
        stream
        (stream-cons (f (stream-first stream)) (maps f (stream-rest stream))))))

reduce.scm

(define reduce
  (lambda (base combiner lst) ;base <object> combiner<function> lst<list>
    (if (null? lst)
      base
      (combiner (head lst)
                (reduce base combiner (tail lst))))))