flet/labels/macrolet

[Jeff Mincy <mincy@Think.COM>]

    Date: Thu 5 Nov 87 00:01:23-PST
    From: "Kim A. Barrett" <IIM@ecla.usc.edu>

      It is our opinion that it is reasonable for a local function/macro to be
    able to shadow a special form.  If such shadowing is not allowed, it's
    basically just another totally arbitrary rule that the programmer has to
    remember.  It also makes for some extra work for program-analyzing
    programs, either in the analysis of flet/labels/macrolet forms, where it
    must check the names to see if they would shadow any of the standard
    special-forms, or at form-processing time (where it is currently impossible
    to do portably).
I, just to be different, do not think that it is reasonable or desirable to
hide special-forms lexically.  These forms really are special, users have to understand
them separately from other things like funtion call.  Making it so that 
could be lexically hidden only makes special forms superficially like other forms.
You still cant funcall a special form. 

      It seems to me that the necessary functionality for examining the
    function environment is pretty easy to describe.  All you really need is
    something like

	(defun local-function-p (symbol environment)
	  "This function returns T if the specified symbol names a local
	   function or macro in the specified environment, and Nil otherwise.
	   Environment should be either the environment argument passed to a
	   macroexpander function (obtained with the &environment
	   lambda-keyword), or the environment argument to applyhook/evalhook."
	   ...)
I have had this problem as well.  One of the few places where I've *HAD* to resort
to #+symbolics ..., #+lucid ...   I would suggest that it return something different
so that lexical macros can be distinguished from lexical functions.
Say return multiple values where the first value is t if is a local function or
macro and the second value of t if the symbol is lexical macro.


      I would expect that, for any given implementation, it is completely
    trivial to write the code for local-function-p.  Does anyone know of a
    counter-example?  With this function available, when your code walker is
    processing a form which is a list whose car is a symbol, it does the
    following


      The functionality needed for augmenting environments is less obvious to
    me, since I haven't studied all that many code walkers to know what their
    needs are, nor all that many implementations, to know what their quirks
    are, as far as manipulation of environments is concerned.  I think
    something like the following would be adequate for the walkers and
    implementations I have seen, but feel free to blow holes in it.
I am not really convinced that this is needed.  But, I havent really thought about it.

    kab

-jeff