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From: amh@cunixb.cc.columbia.edu (Adam M. Heyman)
Newsgroups: comp.lang.scheme
Subject: Are numbers self evaluating?
Message-ID: <1991Feb26.205210.21352@cunixf.cc.columbia.edu>
Date: 26 Feb 91 20:52:10 GMT
Sender: news@cunixf.cc.columbia.edu (The Daily News)
Organization: Columbia University
Lines: 53



While fooling around with MIT Scheme 7.1, found this interesesting phenomena.
Apparently, multidigit numbrs are not self evaluating, they need to go through
adds (+) and multiplies (*) in order to evaluate.
What follows is an edited journal of a session:

	(trace +)
	Automagically impurifying an object...  ;;What the heck does this mean?
	;No value

	1
	;Value: 1
	10
	[Entering #[compound-procedure 2 +]
	    Args: 10
        	  0]
	[10
	      <== #[compound-procedure 2 +]
	    Args: 10
	          0]
	;Value: 10
	123
	[Entering #[compound-procedure 2 +]
	    Args: 10
	          2]
	[12
	      <== #[compound-procedure 2 +]
	    Args: 10
	          2]
	[Entering #[compound-procedure 2 +]
	    Args: 120
	          3]
	[123
	      <== #[compound-procedure 2 +]
	    Args: 120
	          3]
	;Value: 123

etc.

This phenomena holds also for negative numbers, i.e. only -9,-8,...0,...9 are
evaluated without supporting math functions, and can also be seen by tracing
* instead of +.
If anyone out there has some insight as to why Scheme is doing this, please
let me know. I would be very interested to learn why it decomposes numbers,
and then builds them back up (from the point of view of the user, I realize
that the decomposition is probably just the way the input handler functions,
but this is pure conjecture), especially since numbers in scheme are supposed
to be self evaluating.

 Adam Heyman
 amh@cunixb.cc.columbia.edu