[plt-scheme] jumping comma

From: Felix Klock's PLT scheme proxy (pltscheme at pnkfx.org)
Date: Sat Dec 31 11:05:42 EST 2005


For the same reason that you see:
	> (list 'jumping (list 'unquote 'comma))
	(jumping ,comma)

The characters comma (" , "), quote (" ' "), and backquote (" ` ")  
are special characters that are first expanded by the reader into  
unquote, quote, and quasiquote special forms (the reader grabs the  
next S-expression as the argument to the form, and wraps it all in  
parens).  When the evaluator returns an S-expression with unquote,  
quote, or quasiquote in operator position, the printer converts it  
back into a form that uses the shorthand form.


	'(jumping, comma)
= reads to =>
	(quote (jumping (unquote comma)))
= evals to =>
	(jumping (unquote comma))
= prints to =>
	(jumping ,comma)


On Dec 31, 2005, at 7:29 AM, Andreas Zwinkau wrote:

> I don't know, what to make out of this behaviour:
>    > '(jumping, comma)
>    (jumping ,comma)
> Why does the comma jump from "right of jumping" to "left of comma"?
> be blessed
> Andi
> mail: beza1e1 at web.de # jabber: beza1e1 at amessage.de # web:  
> beza1e1.tuxen.de
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