Re: hash tables

[Michael Vanier <mvanier@bbb.caltech.edu>]

> From: "Paul A. Steckler" <steck@cs.rice.edu>
> Cc: "Plt-Scheme@Fast. Cs. Utah. Edu" <plt-scheme@fast.cs.utah.edu>
> Date: Thu, 8 Feb 2001 17:44:06 -0600
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> >It appears that it is not possible to use a string as a key in mzscheme's
> >hash tables.  Is this correct?  I've been able to use symbols and numbers
> >as keys but not strings or immutable strings; why is that?  Also, it would
> >be nice if an error was raised when an invalid key is used, as opposed to
> >finding out later that there is nothing stored at that key location.
> 
> Two Scheme keys hash to the same value iff they are eq?.
> Two strings containing the same characters are not
> eq?.  The *same* string can be used as a hash key,
> but that's rarely what you want.
> 
> You can convert your strings to symbols to use them
> as hash keys.
> 
> The procedure hash-table-get does raise an exception when no value 
> is found.
> 
> -- Paul
> 

OK, I get it now.  I was confused by the error message/exception system
since I was using this interactively (my fault).  Actually, symbols *are*
what I want, but I wanted to know the logic behind it.

Thanks,

Mike