Libraries Digest, Vol 97, Issue 28

John Lato jwlato at
Mon Sep 26 11:35:25 CEST 2011

Message: 6
> Date: Mon, 26 Sep 2011 05:53:05 +0200
> From: Daniel Fischer < at>
> Subject: Proposal: New Eq and Ord instances for Double and Float
> To: libraries at
> Message-ID: < at>
> Content-Type: Text/Plain;  charset="us-ascii"
> Proposal: Provide Double and Float with Eq and Ord instances that introduce
> a total order.

With the current behavior, other data structures (e.g. Data.Set Float)
can be corrupted by NaN.  Silent corruption is an unforgivable sin,
and I think it's worth giving up IEEE semantics for default
comparisons to fix it.

Especially since IEEE floats are often poorly-understand, it's an easy
trap for the unwary, or even the cautious, programmer.

My biggest concern is for the Haskell community at large.  How many
current programs expect (or rely upon) IEEE behavior?  The impact of
this change could be extremely wide-ranging.  I would expect a major
version bump to base to implement this, solely due to the impact.

As to what symbol to use for IEEE comparisons, I dislike the OCaml
dot-style operators precisely because it's easy to overlook.  I don't
have a nice justification for it, but how about two dots, e.g. "==..",
">.." ?

John L

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