Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!yale!Krulwich-Bruce
From: Krulwich-Bruce@cs.yale.edu (Bruce Krulwich)
Newsgroups: comp.lang.scheme
Subject: Re: semantics of DEFINE (why use it at all on the top level?)
Message-ID: <59918@yale-celray.yale.UUCP>
Date: 9 May 89 00:41:32 GMT
References: <890503-103409-9762@Xerox> <2454@ski.cs.vu.nl>
Sender: root@yale.UUCP
Reply-To: Krulwich-Bruce@cs.yale.edu (Bruce Krulwich)
Organization: Computer Science, Yale University, New Haven, CT 06520-2158
Lines: 30
In-reply-to: biep@cs.vu.nl (J A Biep Durieux)

In article <2454@ski.cs.vu.nl>, biep@cs (J A Biep Durieux) writes:
>In article <890503-103409-9762@Xerox> Pavel.pa@XEROX.COM writes:
>
>>-- A program is a mixed sequence of definitions and expressions.
>>	
>>--The meaning of a program P is the same as that of the expression:
>>		    ((lambda  (I*)  P')  <undefined>  ...)
...
>Then why not actually do this?
>
>-- The scheme top-level environment has each variable bound to a unique
>   location.  Many of these locations will be assigned the value 
>   #\undefined.
>
>-- The user can assign other values to variable locations using "set!".
>   A "define" on top level will be an error, since the variable is
>   already bound on that level.

First, the system has to know what symbols to bind in the global LET
contour.  It would be consistant to have DEFINE always specify that a
symbol be included in this binding.

Secondly, having internal DEFINEs do local definitions is even more
redundant, since it is 100% translatable into a LETREC while DEFINE is
needed to specify what variables should be bound.


Bruce Krulwich