How to prevent OCaml batteries from overriding values
The package Batteries.Num overrides the functions (+), (-), ... So the compiler gives an error on the following simple code
open Batteries open Num let a = 4 + 4;;
File "a.ml", line 3, characters 8-9: Error: This expression has type int but an expression was expected of type Batteries.Num.num = Num.num
I compile with "ocamlfind ocamlc -package batteries a.ml".
EDIT: I know I could use Pervasives.(+) or just open Num locally.
But I am able to compile this program successfully with ocamlbuild with the simplest _tags file: <*>: pkg_batteries, package(batteries), package(num)
Where is the magic? How can I compile like ocamlbuild does with a Makefile?
EDIT: I found the solution. I actually had two versions of batteries (1.4 and 2.2), and ocamlfind gave the version 2.2 on command line, and 1.4 on ocamlbuild. I don't know why. I believe the early version of batteries didn't redefine the module Num (but you had to use BatNum), so the problem doesn't occur with the older version. Thanks for the answers.
What command are you using the build it? Because if you aren't specifying a build target (i.e. your command is ocamlbuild a.ml instead of ocamlbuild a.ml a.native) it will appear as though its compiling even though it isn't.
What is ACTUALLY happening when you try "ocamlfind ocamlc -package batteries a.ml" is that the + from nums is overshadowing the + from Pervasives.
You could do let a = Pervasives.(+) 4 4;;, or instead of opening Nums, do Nums. for everything like that.
You can just refer to the function by using the module name you want.
If you want the (+) from Pervasives, you just say Pervasives.(+) x y instead of x + y.
The solution I have used when I faced this problem is to open Pervasive to override Batteries values.
open Batteries open Num open Pervasives let a = 4 + 4;;