Merge branch 'master' of https://github.com/Gavlooth/dst into gavlooth

examples/lazyseqs.dst

@@ -62,7 +62,7 @@ body once, and then memoizes the result."
  (range2 0 end))
 
 (defn map
- "Return a sequence that is the result of apply f to each value in s."
+ "Return a sequence that is the result of applying f to each value in s."
  [f s]
  (delay
   (def x (s))
@@ -105,3 +105,41 @@ body once, and then memoizes the result."
   (when x
    (def thehead (get HEAD x))
    (if thehead (tuple thehead (take-while pred (get TAIL x)))))))
+
+#Iterators is a conscept that looks a lot like lazy seq
+#The following functions turn iterators to lazy seq and vice versa
+
+(defn- iter-self
+  [next]
+  (delay (tuple (next) (iter-self next))))
+
+(defn iter2lazy
+"Create a lazy sequence froma an iterator"
+  [iter]
+  (def  {:more more :next next} iter)
+  (iter-self next))
+
+(defn lazy2iter
+  "turn a lazy-seq to an iterator"
+  [lazy-seq]
+  (var result (head lazy-seq) )
+  (var  rest (tail lazy-seq))
+  {:more  (fn [] result)
+   :next (fn [] (def next result)
+           (when result
+             (:= result (head rest))
+             (:= rest (tail rest)))
+           next)})
+
+
+#Now we can use the nonfuctional filter from boot.dst
+#to write a filter version that returns a lazy sequence
+#Be carefull when creating lazy sequences from mutable
+#data structures as their values are references to this
+#data structures. Same is true for iterators
+
+(defn filter2 [pred coll]
+  (tail (iter2lazy (filter pred coll))))
+
+
+