[plt-scheme] linear update procedures in v4

From: praimon (praimon at gmail.com)
Date: Mon Jan 12 23:41:15 EST 2009

srfi 1 allows, but doesn't require, its linear update procedures to be
destructive. So I was wondering, if I use append! in a version 4 #lang scheme
module, is it 'silently' calling the non-destructive append instead?
As you can see, I'm a bit confused about the mutation-related changes
in the latest versions of plt-scheme.

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