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From: jbs@mit-eddie.MIT.EDU (Jeff Siegal)
Newsgroups: net.lang.lisp
Subject: Re: Abusing "define" in Scheme... (car crashes?)
Message-ID: <2049@mit-eddie.MIT.EDU>
Date: Wed, 21-May-86 06:12:11 EDT
Article-I.D.: mit-eddi.2049
Posted: Wed May 21 06:12:11 1986
Date-Received: Sat, 24-May-86 02:38:32 EDT
References: <13508@ucla-cs.ARPA> <2048@mit-eddie.MIT.EDU>
Reply-To: jbs@mit-eddie.UUCP (Jeff Siegal)
Distribution: net
Organization: MIT, EE/CS Computer Facilities, Cambridge, MA
Lines: 36
Keywords: Scheme

In article <2048@mit-eddie.MIT.EDU> psi@mit-eddie.MIT.EDU (Joseph J. Mankoski) writes:
>In article <13508@ucla-cs.ARPA>, hydar@ucla-cs.ARPA (Dan Hydar) writes:
>> 
>>      
>>         Does anyone know if Scheme is defined such that ANY binding can be
>>    changed or is there some set of functions/identifiers that can be (or
>>    MUST be) prevented from being re-defined?	
>

>[...].  Personally,  I prefer the freedom to
>redefine anything, though  I still avoid redefining  T, Lambda, and of
>course, Define.

Actually, redefining lambda or define would not change the meaning of
expressions like (define a b) or (lambda (x) (* x 2)).  These are are
"special forms" and (if I remember my 6.001 correctly) the evaulator
does not look for their definitions in the current context before
actually doing the work involved (binding or procedure creation).  So
actually the list of indentifiers which can not be redefined is the
list of special forms.

Note however, that you can do the following:

--> (DEFINE LAMBDA 1)
LAMBDA

--> LAMBDA
1

--> ((LAMBDA (X) (+ X 1)) 1)
2

LAMBDA has been defined as a symbol bound to 1, but this does not
affect the normal usage of LAMBDA, which still works as expected(?).

Jeff Siegal