On ocamlyacc, function application grammar and precedence

I'm OCaml newbie and I'm trying to write a simple OCaml-like grammar, and I can't figure this out. My grammar allows something like this:

let sub = fun x -> fun y -> x - y;;

However, if I want to use the function so defined, I can write: (sub 7) 3 but I can't write sub 7 3, which really bugs me. For some reason, it gets interpreted as if I wrote sub (7 3) (which would treat 7 as a function with argument 3). The relevant sections are:

/* other operators, then at the very end: */
%left APPLY

/* ... */

expr:
    /* ... */
    | expr expr %prec APPLY      { Apply($1, $2) }

Thanks!