1 files changed, 60 insertions, 0 deletions
diff --git a/shared/sicp-stream.rkt b/shared/sicp-stream.rkt
new file mode 100644
index 0000000..e7a28d0
--- /dev/null
+++ b/shared/sicp-stream.rkt
@@ -0,0 +1,60 @@
+#lang racket
+(require racket/stream)
+(provide
+ stream-cons
+ stream-car
+ stream-cdr
+ the-empty-stream
+ stream-null?
+ display-line
+ show
+ display-stream
+ stream-ref
+ stream-for-each
+ stream-enumerate-interval
+ stream-map
+ stream-filter)
+
+;; (define (delay b) (lambda () b))
+;; (define (force f) (f))
+;; (define (cons-stream a b) (cons a (delay b)))
+;; (define (cons-stream a b) (stream-cons  a b))
+;; streams in racket by default are not eager for the head of the cons
+(define (stream-car stream) (stream-first stream))
+(define (stream-cdr stream) (stream-rest stream))
+(define the-empty-stream (stream))
+(define (stream-null? stream) (stream-empty? stream))
+(define (display-line x) (newline) (display x))
+(define (show x) (display-line x) x)
+(define (display-stream s) (stream-for-each display-line s))
+
+(define (stream-ref s n)
+    (if (= n 0)
+        (stream-car s)
+        (stream-ref (stream-cdr s) (- n 1))))
+
+(define (stream-for-each proc s)
+    (if (stream-null? s)
+        'done
+        (begin (proc (stream-car s))
+               (stream-for-each proc (stream-cdr s)))))
+
+(define (stream-enumerate-interval low high)
+    (if (> low high)
+        the-empty-stream
+        (stream-cons
+         low
+         (stream-enumerate-interval (+ low 1) high))))
+
+(define (stream-map proc . argstreams)
+    (if (stream-null? (car argstreams))
+        the-empty-stream
+        (stream-cons
+         (apply proc (map stream-car argstreams))
+         (apply stream-map
+                (cons proc (map stream-cdr argstreams))))))
+
+(define (stream-filter pred s)
+    (cond ((stream-null? s) the-empty-stream)
+          ((pred (stream-car s)) (stream-cons  (stream-car s) (stream-filter pred (stream-cdr s))))
+          (else (stream-filter pred (stream-cdr s)))))