One way to convert data structures into human readable form (and to then operate on that representation) is to use the Core.Std s-expressions; they're basically modeled after LISP s-expressions and Core.Std has functionality to convert data from and to s-expressions (and a syntax extension to automate most of the boring parts). You can find a good overview in chapter 17 of Real World OCaml.
Most importantly for your application, there is already functionality to compute a diff between to s-expressions (you can also pretty-print them and then use a normal textual diff on them). This functionality can be found in Core_extended.Std.Sexp.Diff.
Example:
open Core.Std (* basic Sexp functionality. *)
module XSexp = Core_extended.Std.Sexp (* for Sexp diffs. *)
type example = {
a: string;
b: int;
c: float;
} with sexp (* syntax extension *)
let v1 = { a = "foo"; b = 1; c = 3.14 }
let v2 = { a = "bar"; b = 2; c = 3.14 }
let print_sexp s = print_endline (Sexp.to_string_hum s)
let sexp_diff s1 s2 =
match XSexp.Diff.of_sexps ~original:s1 ~updated:s2 with
None -> ""
| Some(diff) -> XSexp.Diff.to_string diff
let main () =
let s1 = sexp_of_example v1 in
let s2 = sexp_of_example v2 in
print_endline "=== first sexp ===";
print_sexp s1;
print_endline "=== second sexp ===";
print_sexp s2;
print_endline "=== print_diff output ===";
XSexp.print_diff ~oc:stdout ~original:s1 ~updated:s2 ();
print_endline "=== sexp_diff output ===";
print_endline (sexp_diff s1 s2)
let () = main ()
Here, print_diff is a predefined function to print the diff to a channel and sexp_diff is a simple custom function that uses Sexp.Diff to return the diff as a string. After building the program with corebuild -pkg core_extended example.native (or .byte, or using ocamlbuild with the necessary arguments), running the program should produce the following output:
=== first sexp ===
((a foo) (b 1) (c 3.14))
=== second sexp ===
((a bar) (b 2) (c 3.14))
=== print_diff output ===
a
- foo
+ bar
b
- 1
+ 2
=== sexp_diff output ===
a
- foo
+ bar
b
- 1
+ 2
