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<H2><A NAME="SECTION00061000000000000000"> </A>
<A NAME="input-terms"> </A>
<BR>
Defining Terms
</H2>
<P>
The input structure of terms is borrowed from the Synthesizer's
Specification Language SSL.
<A NAME="112"> </A>
An example is the following.
<A NAME="113"> </A><A NAME="114"> </A>
<PRE><HR><!--lgrindfile: phylum_example.k 12:12 Jan 17 1997-->
expr: Plus(expr expr)
| Minus(expr expr)
| Neg(expr)
| Zero()
;
<BR>
exprlist: <B>list</B> expr;
<HR></PRE>
This declares two
<EM>phyla</EM><A NAME="117"> </A>,
or term types, or nonterminals, depending on your viewpoint.
Each of these denotes a set of terms.
As shown, there are two ways of constructing a phylum.
One is by enumerating its variants, each of which is an
<EM>operator</EM>
<A NAME="119"> </A>
applied to a list of phyla.
It is possible to declare nullary operators, but it is not possible to define
phyla that do not have operators.
The other way is declaring it as a
<I>list</I>
phylum.
<A NAME="121"> </A>
This is effectively equivalent to declaring the following right recursive
phylum:
<A NAME="122"> </A>
<PRE><HR><!--lgrindfile: list_phylum_example.k 19:44 Oct 21 1992-->
exprlist:Nilexprlist()
| Consexprlist(expr exprlist)
;
<HR></PRE>
<P>
A list phylum therefore always has an empty list constructor, and a prefix operator.
The advantage of a list declaration, apart from its brevity, is that it
instructs the system to generate additional, list-specific, functions.
<P>
There are a number of predefined phyla, among them are
<I>casestring</I>
<A NAME="1342"> </A>
and
<I>nocasestring</I>
<A NAME="1343"> </A>
for case-sensitive and case-insensitive character strings respectively.
The full list of predefined phyla is in Section <A HREF="node18.html#gen-predef">2.3</A>.
<P>
<P>
Phyla can be defined more than once, and at each occurrence operators, attributes,
and storage options (see below) can be added.
<P>
For each phylum, the term processor generates a C data type (a record)
with the same name.
This is discussed in more detail in Section <A HREF="node16.html#gen-types">2.1</A>.
<P>
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<BR><I>2000-04-17</I>
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