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Re: [Chicken-users] Bug with #!optional in Chicken 4.8.0

From: John Cowan
Subject: Re: [Chicken-users] Bug with #!optional in Chicken 4.8.0
Date: Wed, 17 Oct 2012 10:01:15 -0400
User-agent: Mutt/1.5.20 (2009-06-14)

John Croisant scripsit:

> Here is how I understand the situation: in order to avoid
> unnecessary computation, we want to avoid invoking the guard
> procedure when the old parameter value is restored at the end of
> parameterize. 

This is not strong enough: despite the term "guard procedure", this
procedure can in fact compute and return arbitrary results, so it
must not be called on restore, and doing so is a correctness
violation, not merely an optimization.  Indeed, SRFI 39 calls it a
conversion procedure.

A: "Spiro conjectures Ex-Lax."                  John Cowan
Q: "What does Pat Nixon frost her cakes with?"  address@hidden
  --"Jeopardy" for generative semanticists

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