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WarnUnusedAnomalies
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The <tt>warnUnused</tt> <a href="MLBasisAnnotations">MLBasis annotation</a> can be used to report unused identifiers. This can be useful for catching bugs and for code maintenance (e.g., eliminating dead code). However, the <tt>warnUnused</tt> annotation can sometimes behave in counter-intuitive ways. This page gives some of the anomalies that have been reported.
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Functions whose only uses are recursive uses within their bodies are not warned as unused:
<pre class=code>
<B><FONT COLOR="#0000FF">local</FONT></B>
<B><FONT COLOR="#A020F0">fun</FONT></B> foo () = foo () : unit
<B><FONT COLOR="#A020F0">val</FONT></B> bar = <B><FONT COLOR="#A020F0">let</FONT></B> <B><FONT COLOR="#A020F0">fun</FONT></B> baz () = baz () : unit <B><FONT COLOR="#A020F0">in</FONT></B> baz <B><FONT COLOR="#A020F0">end</FONT></B>
<B><FONT COLOR="#0000FF">in</FONT></B>
<B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
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<pre>Warning: z.sml 3.5.
Unused variable: bar.
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Components of actual functor argument that are necessary to match the functor argument signature but are unused in the body of the functor are warned as unused:
<pre class=code>
<B><FONT COLOR="#0000FF">functor</FONT></B> Warning (<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x : t) = <B><FONT COLOR="#0000FF">struct</FONT></B>
<B><FONT COLOR="#A020F0">val</FONT></B> y = x
<B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">structure</FONT></B> X = Warning (<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x = <B><FONT COLOR="#5F9EA0">1</FONT></B>)
</PRE>
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<pre>Warning: z.sml 4.29.
Unused type: t.
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No component of a functor result is warned as unused. In the following, the only uses of <tt>f2</tt> are to match the functor argument signatures of <tt>functor G</tt> and <tt>functor H</tt> and there are no uses of <tt>z</tt>:
<pre class=code>
<B><FONT COLOR="#0000FF">functor</FONT></B> F(<B><FONT COLOR="#0000FF">structure</FONT></B> X : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>) = <B><FONT COLOR="#0000FF">struct</FONT></B>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> X.t
</FONT></B><B><FONT COLOR="#A020F0">fun</FONT></B> f1 (_ : X.t) = ()
<B><FONT COLOR="#A020F0">fun</FONT></B> f2 (_ : X.t) = ()
<B><FONT COLOR="#A020F0">val</FONT></B> z = ()
<B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">functor</FONT></B> G(<B><FONT COLOR="#0000FF">structure</FONT></B> Y : <B><FONT COLOR="#0000FF">sig</FONT></B>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
</FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> f1 : t -> unit
<B><FONT COLOR="#A020F0">val</FONT></B> f2 : t -> unit
<B><FONT COLOR="#A020F0">val</FONT></B> z : unit
<B><FONT COLOR="#0000FF">end</FONT></B>) = <B><FONT COLOR="#0000FF">struct</FONT></B>
<B><FONT COLOR="#A020F0">fun</FONT></B> g (x : Y.t) = Y.f1 x
<B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">functor</FONT></B> H(<B><FONT COLOR="#0000FF">structure</FONT></B> Y : <B><FONT COLOR="#0000FF">sig</FONT></B>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
</FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> f1 : t -> unit
<B><FONT COLOR="#A020F0">val</FONT></B> f2 : t -> unit
<B><FONT COLOR="#A020F0">val</FONT></B> z : unit
<B><FONT COLOR="#0000FF">end</FONT></B>) = <B><FONT COLOR="#0000FF">struct</FONT></B>
<B><FONT COLOR="#A020F0">fun</FONT></B> h (x : Y.t) = Y.f1 x
<B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">functor</FONT></B> Z() = <B><FONT COLOR="#0000FF">struct</FONT></B>
<B><FONT COLOR="#0000FF">structure</FONT></B> S = F(<B><FONT COLOR="#0000FF">structure</FONT></B> X = <B><FONT COLOR="#0000FF">struct</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> unit </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>)
<B><FONT COLOR="#0000FF">structure</FONT></B> SG = G(<B><FONT COLOR="#0000FF">structure</FONT></B> Y = S)
<B><FONT COLOR="#0000FF">structure</FONT></B> SH = H(<B><FONT COLOR="#0000FF">structure</FONT></B> Y = S)
<B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">structure</FONT></B> U = Z()
<B><FONT COLOR="#A020F0">val</FONT></B> _ = U.SG.g ()
<B><FONT COLOR="#A020F0">val</FONT></B> _ = U.SH.h ()
</PRE>
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Last edited on 2007-11-01 18:32:19 by <span title="fenrir.uchicago.edu"><a href="MatthewFluet">MatthewFluet</a></span>.
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