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Re: Worrying development

From: Tom Lord
Subject: Re: Worrying development
Date: Fri, 23 Jan 2004 09:16:25 -0800 (PST)

    > From: Dirk Herrmann <address@hidden>

    > First: It's not a matter of whether users *need* to make certain 
    > assumptions: It's a matter of interface definition. Scheme defines the 
    > string data type and together with it, it defines the semantics of 
    > operations on it. 

Please show me what existing lines of the Scheme standard will have to
change if mutation-sharing shared substrings are added.

The standard (not very formally but clearly enough) says that the
standard procedures which construct strings allocate fresh locations
for the contents of those strings.

That means that none of those procedures create mutation-sharing
shared substrings -- nobody has proposed anything different.

I think you are imagining that there is an additional requirement in
the standard: that any procedure at all which creates a new string
must allocate fresh locations for its contents.  But that additional
requirement isn't there.  Scheme programmers can not assume that that
requirement is part of Scheme.

Mutation-sharing shared substrings are an upwards compatible extension
to the Scheme standard.  They break no correct programs.  They enable
new kinds of programs.


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