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<TITLE>4.1 The Danger of Modifying Languages</TITLE>
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<A HREF="compile.html"><FONT COLOR="#FFFFFF">1 Compile</FONT></A><BR>
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<P><FONT SIZE="5">4.1 The Danger of Modifying Languages</FONT><BR>
<P>FunnelWeb is a computer program that implements the
semantics of the FunnelWeb language. As such, you should
take great care when making changes to FunnelWeb that
modify the syntax or semantics of its language:
<P><BLOCKQUOTE><B>Removing
features:</B> Removal of features
(featurectomy) is extremely difficult once the legacy base
is using the features. If a feature is removed, users will
have to go through all their files and find
a way to simulate the effect of the removed feature with
other features. This is usually unthinkable.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Modifying
features:</B> Modification of
features has less direct impact than the removal of
features, but can cause more subtle errors. Anyone modifying
features should be sure that they
are not inadvertently laying semantic traps.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Adding
features:</B> Although the addition
of features is generally the most painless for the user
community, as Hoare points out, it is also the most
dangerous in the long run.</BLOCKQUOTE>
<P>
<BLOCKQUOTE> "When any new language
design project is nearing completion, there is always a mad
rush to get new features added before standardization. The
rush is mad indeed, because it leads into a trap from which
there is no escape. A feature which is omitted can always be
added later, when its design and its implications are well
understood. A feature which is included before it is fully
understood can never be removed later."<STRONG>[Hoare80]</STRONG>
</BLOCKQUOTE>
<P>The benefits of tight control over a language are
enormous.
<P><BLOCKQUOTE><B>Universal portability:</B> Source files can be
treated as portable.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Clear semantics:</B> Doubt about the semantics
of the language are minimized.</BLOCKQUOTE>
<P>For these reasons, I have decided to keep tight control
over the FunnelWeb syntax and semantics. If you develop
a variant of FunnelWeb, please take these issues into account.
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