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1.1       root        1: \chapter{Directives}
                      2: Directives are included in ML as (syntactically) a subclass of declarations.
                      3: They possess scope, as do all declarations.  The directives
                      4: \begin{quote}
                      5: \verb"infix" {\it d} ${\bf id}_1$ \underline{\ \ \ } ${\bf id}_n$
                      6: 
                      7: \verb"infixr" {\it d} ${\bf id}_1$ \underline{\ \ \ } ${\bf id}_n$
                      8: \end{quote}
                      9: introduce infix status for the identifiers  ${\bf id}_1$  through ${\bf id}_n$.
                     10: The digit $d$ (optional, with a default of 0) determines the
                     11: precedence, and an infixed identifier associates to the left if
                     12: introduced by \verb"infix", and to the right if introduced by
                     13: \verb"infixr".  Different infixed operators of equal precedence
                     14: associate to the left.  As indicated in Appendix~\ref{grammar}, the precedence
                     15: of infixed application is just weaker than that of application.
                     16: 
                     17: The directive
                     18: \begin{quote}
                     19: \verb"nonfix" ${\bf id}_1$ \underline{\ \ \ } ${\bf id}_n$
                     20: \end{quote}
                     21: cancels infix status for the named identifiers.
                     22: 
                     23: While an identifier has infix status, each occurrence of it (as a
                     24: value variable or as a constructor) must be infixed or else preceded
                     25: by \verb"op".  Note that this includes occurrences of the identifier
                     26: within patterns, even binding occurrences of variables.
                     27: 
                     28: Several standard functions and constructors have infix status (see
                     29: Appendix~\ref{grammar}) with precedence; these are all left associative except
                     30: ``\verb"::"''.

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