Add a pair sampler generator

Author: adhameer

src/grader/test_lib.ml

@@ -119,6 +119,7 @@ module type S = sig
     val sample_bool : bool sampler
     val sample_list : ?min_size: int -> ?max_size: int -> ?dups: bool -> ?sorted: bool -> 'a sampler -> 'a list sampler
     val sample_array : ?min_size: int -> ?max_size: int -> ?dups: bool -> ?sorted: bool -> 'a sampler -> 'a array sampler
+    val sample_pair : 'a sampler -> 'b sampler -> ('a * 'b) sampler
     val sample_alternatively : 'a sampler list -> 'a sampler
     val sample_cases : 'a list -> 'a sampler
     val sample_option : 'a sampler -> 'a option sampler
@@ -1862,6 +1863,9 @@ module Make
     let sample_list ?min_size ?max_size ?dups ?sorted sample () =
       Array.to_list (sample_array ?min_size ?max_size ?dups ?sorted sample ())
 
+    let sample_pair sample1 sample2 () =
+      (sample1 (), sample2 ())
+
     let printable_funs = ref []
 
     let fun_printer ppf f =

src/grader/test_lib.mli

@@ -472,6 +472,11 @@ module type S = sig
       -> 'a sampler
       -> 'a array sampler
 
+    (** [sample_pair s1 s2] returns a sampler that generates a value
+        of type ['a * 'b] using [s1] and [s2] to generate values of
+        type ['a] and ['b], respectively, on each call. *)
+    val sample_pair : 'a sampler -> 'b sampler -> ('a * 'b) sampler
+
     (** [sample_alternatively s] returns a sampler that mimics
        randomly the behavior of one of [s] sampler and change at each
        call. *)