fix ocaml build by moving to Zarith methods

Author: bronsa

src/api/ml/z3.ml

@@ -1039,7 +1039,7 @@ struct
     let get_big_int (x:expr) =
       if is_int_numeral x then
         let s = (Z3native.get_numeral_string (Expr.gc x) x) in
-        Big_int.big_int_of_string s
+        Z.of_string s
       else
         raise (Error "Conversion failed.")
 
@@ -1063,7 +1063,7 @@ struct
     let get_ratio x =
       if is_rat_numeral x then
         let s = Z3native.get_numeral_string (Expr.gc x) x in
-        Ratio.ratio_of_string s
+        Q.of_string s
       else
         raise (Error "Conversion failed.")
 

src/api/ml/z3.mli

@@ -1159,7 +1159,7 @@ sig
     val mk_sort : context -> Sort.sort
 
     (** Get a big_int from an integer numeral *)
-    val get_big_int : Expr.expr -> Big_int.big_int
+    val get_big_int : Expr.expr -> Z.t
 
     (** Returns a string representation of a numeral. *)
     val numeral_to_string : Expr.expr -> string
@@ -1217,7 +1217,7 @@ sig
     val get_denominator : Expr.expr -> Expr.expr
 
     (** Get a ratio from a real numeral *)
-    val get_ratio : Expr.expr -> Ratio.ratio
+    val get_ratio : Expr.expr -> Q.t
 
     (** Returns a string representation in decimal notation.
         The result has at most as many decimal places as indicated by the int argument.*)