[Caml-list] polymorphic (<)

[Jacques Le Normand]

Hello caml-list,
Why doesn't (<) check for physical equality before traversing the
structures?
--Jacques L.

[Martin Jambon]

Jacques Le Normand wrote:
> Hello caml-list,
> Why doesn't (<) check for physical equality before traversing the
> structures?

If I remember correctly it used to be the case in older versions of OCaml, but
it changed because of the standard behavior expected from NaN float values.
The comparison of a NaN value with any other float should always return false,
and therefore the structural comparison of any data structure containing a NaN
with itself should also return false:

# let x = Some [ nan ];;
val x : float list option = Some [nan]

# x = x;;
- : bool = false

# x == x;;
- : bool = true

The solution to your problem is to use Pervasives.compare instead of the
comparison operators:

# compare x x;;
- : int = 0

Martin

--
http://mjambon.com/

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