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section on record update in gf-refman

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aarne
2014-06-19 07:10:43 +00:00
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doc/gf-refman.html
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@@ -5,7 +5,7 @@
</HEAD><BODY BGCOLOR="white" TEXT="black"> </HEAD><BODY BGCOLOR="white" TEXT="black">
<P ALIGN="center"><CENTER><H1>GF Language Reference Manual</H1> <P ALIGN="center"><CENTER><H1>GF Language Reference Manual</H1>
<FONT SIZE="4"> <FONT SIZE="4">
<I>Aarne Ranta</I>, <I>Krasimir Angelov</I><BR>November 2013 <I>Aarne Ranta</I>, <I>Krasimir Angelov</I><BR>June 2014, GF 3.6
</FONT></CENTER> </FONT></CENTER>
<P></P> <P></P>
@@ -2490,8 +2490,20 @@ The result is a record type or a record with a union of the fields of <I>R</I> a
</P> </P>
<UL> <UL>
<LI>both <I>R</I> and <I>S</I> are either records or record types <LI>both <I>R</I> and <I>S</I> are either records or record types
<LI>the labels in <I>R</I> and <I>S</I> are distinct <LI>the labels in <I>R</I> and <I>S</I> are disjoint, if <I>R</I> and <I>S</I> are record types
</UL> </UL>
(Since GF version 3.6) If <I>R</I> and <I>S</I> are record objects,
then the labels in them need not be disjoint. Labels defined in
<I>S</I> are then given priority, so that record extensions in fact
works as <B>record update</B>. A common pattern of using this feature
is
<pre>
lin F x ... = x ** {r = ... x.r ...}
</pre>
where <tt>x</tt> is a record with many fields, just one of which is
updated. Following the normal binding conditions, <tt>x.r</tt> on the
right hand side still refers to the old value of the <tt>r</tt> field.
<A NAME="toc41"></A> <A NAME="toc41"></A>
<H3>Subtyping</H3> <H3>Subtyping</H3>