[plt-dev] `unsafe-fl' and unboxing

From: Doug Williams (m.douglas.williams at gmail.com)
Date: Sun Oct 4 14:46:48 EDT 2009

When you use mutable data structures, you live with the choice. For the
statistics routines, I use exact->inexact inside the loop at the point where
I use the value, so I'm not worried about it. Off the top of my head, the
only problem I see is that exact->inexact also works on complex numbers, so
I may still not have a simple float. I assume +inf.0, -inf.0, and +nan.0
(and, therefore, -nan.0) also pass through exact->inexact. I further assume
those are stored as floats (in an IEEE format) and work as expected - at
least they seem to in the REPL. Is that a correct assumption? Are there
other cases where exact->inexact does not give me a float? [I need to decide
on a case by case basis what to do about complex numbers.]

On Sun, Oct 4, 2009 at 12:53 PM, Matthew Flatt <mflatt at cs.utah.edu> wrote:

> At Sat, 3 Oct 2009 08:34:03 -0600, Matthew Flatt wrote:
> > (while the contract on the "checked" version ensures that the unsafe
> > operations will not cause a crash).
> Not true. Sam points out that a vector (or other sequence) can be
> mutable, so checking elements at the beginning does not make `variance'
> safe if it uses unsafe operations on the elements internally.
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