`val (-->) : 'a t -> int -> 'a`

`map-->key` returns the current binding of `key` in `map`.

- raises `Not_found`

  if no such binding exists.

Equivalent to `find key map`.

`val (<--) : 'a t -> (int * 'a) -> 'a t`

`map<--(key, value)` returns a map containing the same bindings as `map`, plus a binding of `key` to `value`. If `key` was already bound in `map`, its previous binding disappears. Equivalent to `add key value map`

Important warning: `BatIMap.add` takes an optional argument, `eq` that is missing in this operator `<--`. As a consequence, using `<--` implies the use of Pervasives.(==) as comparison function.