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need for 'dynamical-let'?

From: Stephen J. Turnbull
Subject: need for 'dynamical-let'?
Date: Fri, 24 Jul 2015 13:23:34 +0900

Stephen Leake writes:

 > Can we define a macro 'dynamical-let' that would implement this
 > pattern, but with hidden variables?

First, was there a typo in your post?  add-to-list normally takes a
(quoted) symbol.  Since the argument isn't quoted, it appears that the
effect is that you are attempting to add-to-list to the variable (not
the value!) nil.  Assuming that was a typo....

`dynamical-let' is about as ugly as ugly can get, and anyway it
shouldn't be necessary.  The variable is lexically apparent and its
value is not magical in any way.  Your code *should* work.

Try running your code in the interpreter.  I suspect it will work when
the function is actually called (in compiled code there's a compiler
macro so the function is never called).  Why not fix that instead?

Or, perhaps, as Dmitry and the add-to-list docstring suggest, you
should convert the code to use `push' or `pushnew' instead.  The
inconvenience of the busybody compiler macro may be considered a
"feature" intended to encourage you to modernize your code.

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