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>2.7. Generating Multiple Parsers From a Single Grammar</A
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><P
>It is often useful to use a single grammar to describe
multiple parsers, where each parser has a different top-level
non-terminal, but parts of the grammar are shared between
parsers. A classic example of this is an interpreter, which
needs to be able to parse both entire files and single
expressions: the expression grammar is likely to be identical
for the two parsers, so we would like to use a single grammar
but have two entry points.</P
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> lets you do this by
allowing multiple <TT
CLASS="LITERAL"
>%name</TT
> directives in the
grammar file. The <TT
CLASS="LITERAL"
>%name</TT
> directive takes an
optional second parameter specifying the top-level
non-terminal for this parser, so we may specify multiple parsers
like so:</P
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>%name parse1 non-terminal1
%name parse2 non-terminal2</PRE
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> will generate from this a
module which defines two functions <TT
CLASS="FUNCTION"
>parse1</TT
>
and <TT
CLASS="FUNCTION"
>parse2</TT
>, which parse the grammars given
by <TT
CLASS="LITERAL"
>non-terminal1</TT
> and
<TT
CLASS="LITERAL"
>non-terminal2</TT
> respectively. Each parsing
function will of course have a different type, depending on the
type of the appropriate non-terminal.</P
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