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Date: Saturday, 7 March 1987 18:39-EST
From: Jeff Dalton <jeff%aiva.edinburgh.ac.uk at Cs.Ucl.AC.UK>
To: johnw%cvaxa.sussex.ac.uk at Cs.Ucl.AC.UK
cc: common-lisp at sail.stanford.edu
Re: evalhook, eval-when
A key question here is whether Common Lisp requires that the environment
obtained via the &ENV parameter of a macro can meaningfully be passed to
EVALHOOK and vice-versa.
The answer is no. See pp145-146 in CLTL in the discussion of the
(omitted) &environment keyword. I believe PCL is no longer doing
this, since it works on our system which uses a partial environment
In any case, POPLOG Common Lisp might still have some use for hook
functions. [...] As a user of POPLOG Common Lisp, I often wish
there was a single stepper of some sort, even if it didn't see
forms "smaller than function calls".
Yes, evalhook is one way to implement a stepper. The question is
whether providing a portable way to implement steppers is so important
that we make life difficult for implementors by requiring it in Common
Lisp. There is nothing to stop compile-only implementations from
having steppers, but they probably aren't going to want to use
evalhook to do it.