doc/refintro.tex: Fix indexed-nonterminal argument abbreviation.

[sod] / doc / refintro.tex

diff --git a/doc/refintro.tex b/doc/refintro.tex
index 2d4dbed..b0626c3 100644 (file)
--- a/doc/refintro.tex
+++ b/doc/refintro.tex
@@ -90,6 +90,11 @@ manual describes the base system as provided in the distribution.
 Fortunately, Sod is syntactically quite simple.  The notation is slightly
 unusual in order to make the presentation shorter and easier to read.
 
+The letter $\epsilon$ denotes the empty nonterminal
+\begin{quote}
+  \syntax{$\epsilon$ ::=}
+\end{quote}
+
 Anywhere a simple nonterminal name $x$ may appear in the grammar, an
 \emph{indexed} nonterminal $x[a_1, \ldots, a_n]$ may also appear.  On the
 left-hand side of a production rule, the indices $a_1$, \ldots, $a_n$ are
@@ -98,10 +103,20 @@ variables may also appear on the right-hand side in place of a nonterminal.
 Such a rule stands for a family of rules, in which each variable is replaced
 by each possible simple nonterminal or terminal symbol.
 
-The letter $\epsilon$ denotes the empty nonterminal
+As a notational convenience, where an indexed nonterminal appears on the
+right-hand side of a production rule, each actual argument may be a sequence
+of alternative right-hand sides, separated by `$|$', rather than a a simple
+terminal or nonterminal symbol.  A complex indexing of this form, say
+\syntax{$x$@[$\alpha_1^1$ @! $\alpha_1^2$ $| \cdots |$ $\alpha_1^{m_1},
+\ldots,$ $\alpha_n^1$ @! $\alpha_n^2$ $| \cdots |$ $\alpha_n^{m_n}$@]}
+means exactly the same as \syntax{$x$@[$a_1, \ldots, a_n$@]} with the
+additional rules
 \begin{quote}
-  \syntax{$\epsilon$ ::=}
+  \syntax{$a_1$ ::= $\alpha_1^1$ @! $\alpha_1^2$ $| \cdots |$ $\alpha_1^{m_1}$} \\*
+  \hbox{}\qquad $\vdots$ \\*
+  \syntax{$a_n$ ::= $\alpha_n^1$ @! $\alpha_n^2$ $| \cdots |$ $\alpha_1^{m_n}$}
 \end{quote}
+where $a_1$, \ldots, $a_n$ are new nonterminal symbols.
 
 The following indexed productions are used throughout the grammar, some often
 enough that they deserve special notation.