add lab 07 doc comments

labs/07/primes.ml

@@ -1,15 +1,31 @@
+(** An infinite stream containing values of type ['a],
+  * where the tail is produced by a thunk.
+  *)
 type 'a infstream = Cons of 'a * (unit -> 'a infstream)
 
+(** [take n s] returns a list containing the first [n] elements
+  * of infinite stream [s].
+  * If [n <= 0], it returns the empty list.
+  *)
 let rec take n (Cons (h, t)) =
   if n <= 0 then []
   else h :: take (n - 1) (t ())
 
+(** [from n] creates an infinite stream of integers starting at [n]
+  * and increasing by [1] for each subsequent element.
+  *)
 let rec from n = Cons (n, fun () -> from (n + 1))
 
+(** [filter f s] returns a new infinite stream containing only
+  * the elements of stream [s] that satisfy predicate [f].
+  *)
 let rec filter f (Cons (h, t)) =
   if f h then Cons (h, fun () -> filter f (t ()))
   else filter f (t ())
 
+(** [primes] is an infinite stream of prime numbers generated
+  * using the sieve of Eratosthenes.
+  *)
 let primes =
   let rec sieve (Cons (h, t)) =
     Cons (h, fun () ->