[PD] Finding "$0" and dealing with it in messages

Mathieu Bouchard matju at artengine.ca
Fri Dec 4 21:59:16 CET 2009

On Sat, 28 Nov 2009, Frank Barknecht wrote:

> I encountered this in the SICP as well which is from 1984, so probably 
> knows its Smalltalk as well, although the index only mentions Smalltalk 
> once in a footnote.
> Here's the intro to selectors:
> http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-14.html#%_idx_1290

This is not the same meaning of selector. We have to be careful about 
that. In mainstream OO vocabulary, this would be called «reader», 
«getter», or «accessor» (or half of an accessor), although in your 
example, they define these as plain functions because there is no OO in 

In Scheme, the concept of selector we are talking about does not exist. In 
CommonLISP, it would be called «the symbol of a generic-function» because 
when CommonLISP integrated the notion of OO it turned it quite inside-out.

I don't know about other OOP frameworks for LISP and Scheme but you can 
assume that there are as many as there are for Tcl. In those systems you 
may find a more ordinary concept of selector. Or not.

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| Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801

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