[OCaml] Fix some of the OCaml examples

Update some of the OCaml examples so that they run successfully with
`make check-ocaml-examples` (important for the CI). Some of the
examples were written to depend on passed arguments.

Temporarily disable the broken std_string example.

Examples/ocaml/argout_ref/example_prog.ml

@@ -5,17 +5,8 @@ open Example
 
 exception BadReturn
 
-let _ = if Array.length Sys.argv < 3 then
-  begin
-    print_endline 
-      ("Usage: " ^ Sys.argv.(0) ^ " n1 n2\n" ^
-       " Displays the least factors of the numbers that have the same\n" ^
-       " relationship, 16 12 -> 4 3\n") ;
-    exit 0
-  end
-
-let x = int_of_string Sys.argv.(1)
-let y = int_of_string Sys.argv.(2)
+let x = if Array.length Sys.argv > 1 then int_of_string Sys.argv.(1) else 16
+let y = if Array.length Sys.argv > 2 then int_of_string Sys.argv.(2) else 12
 let (xf,yf) = match _factor '((x to int),(y to int)) with
     C_list [ C_int a ; C_int b ] -> a,b
   | _ -> raise BadReturn

Examples/ocaml/check.list

@@ -1,6 +1,6 @@
 # see top-level Makefile.in
 simple
-std_string
+#std_string
 std_vector
 stl
 argout_ref

Examples/ocaml/contract/example_prog.ml

@@ -4,4 +4,9 @@ open Example
 let _ = print_endline "This won't throw." 
 let _ = Printf.printf "Cos 1.0 is %f\n" (_cos '(1.0) as float)
 let _ = print_endline "This will throw."
-let _ = Printf.printf "Cos 5.0 is %f\n" (_cos '(5.0) as float)
+let _ =
+  try
+    Printf.printf "Cos 5.0 is %f\n" (_cos '(5.0) as float)
+  with Failure s ->
+    print_endline s ;
+    print_endline "Exception thrown."

Examples/ocaml/scoped_enum/example_prog.ml

@@ -1,4 +1,5 @@
 open Swig
 open Example
 
-let _ = _f (match Sys.argv.(1) with "Tag1" -> ``Tag1 | _ -> ``Tag2)
+let arg = if Array.length Sys.argv > 1 then Sys.argv.(1) else "Tag1"
+let _ = _f (match arg with "Tag1" -> ``Tag1 | _ -> ``Tag2)

Examples/ocaml/strings_test/example.i

@@ -11,4 +11,5 @@ using std::string;
 #include "example.h"
 %}
 
+%include "std_string.i"
 %include example.h