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<H2><A NAME="SECTION00062000000000000000"> </A>
<A NAME="attr-terms-input"> </A>
<BR>
Attributes of Terms
</H2>
<P>
Phyla can be declared to have
<EM>attributes</EM>
<A NAME="133"> </A>
of a predeclared type.
This type can be any C type, e.g. <I>int</I>, or <I>float</I>.
Of course, it can also be a C type that is generated by <EM>Kimwitu</EM>.
An example phylum with attributes is:
<A NAME="137"> </A>
<PRE><HR><!--lgrindfile: attributed_phylum_example.k 12:13 Jan 17 1997-->
expr: Plus(expr expr)
| Minus(expr expr)
| Neg(expr)
| Zero()
{ <B>float</B> value = 0;}
;
<HR></PRE>
Here the attribute
<I>value</I>
of type
<I>float</I>
is defined, and initialised with <I>0</I>.
<A NAME="142"> </A>
Multiple attributes can be defined between the curly brackets.
The initialisations are optional.
The type of an attribute can also be a type generated by the term
processor (such as a phylum).
<P>
Attributes serve as a facility to decorate a tree with extra information.
The decoration can be done in arbitrary user code.
The attribute becomes a component of the record that is generated for the phylum.
If <I>x</I> is a value of type <I>expr</I>, then the attribute can be referred to as
<I>x</I>
<!-- MATH: $\rightarrow$ -->
<IMG
WIDTH="19" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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ALT="$\rightarrow$"><I>value</I>.
<P>
As the last item of the initialisation a piece
of arbitrary C, enclosed in curly brackets, is allowed.
In this code the expression <I>$0</I> denotes the term that is being created.
The code is executed after the term has been built completely, and the other
initialisations have been performed.
An alternative way of expressing the above initialisation therefore is:
<PRE><HR><!--lgrindfile: alternative_attribute_initialisation.k 19:44 Oct 21 1992-->
{ <B>float</B> value;
{ $0->value=0;}}
<HR></PRE>
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