gf-core/lib/resource/doc/gfdoc/Precedence.html

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Last update: 2005-11-23 09:16:18 CET
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Produced by
gfdoc - a rudimentary GF document generator.
(c) Aarne Ranta (<A HREF="mailto:aarne@cs.chalmers.se">aarne@cs.chalmers.se</A>) 2002 under GNU GPL.
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<P>
operations for precedence-dependent strings.
five levels:
p4 (constants), p3 (applications), p2 (products), p1 (sums), p0 (arrows)
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<PRE>
    resource Precedence = open Prelude in {

    param
    Prec = p4 | p3 | p2 | p1 | p0 ;

    lintype
    PrecTerm = Prec =&gt; Str ;

    oper
    pss : PrecTerm -&gt; {s : PrecTerm} = \s -&gt; {s = s} ;
</PRE>
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<P>
change this if you want some other type of parentheses
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<PRE>
    mkParenth : Str -&gt; Str = \str -&gt; "(" ++ str ++ ")" ;
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<P>
define ordering of precedences
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<PRE>
    nextPrec : Prec =&gt; Prec =
      table {p0 =&gt; p1 ; p1 =&gt; p2 ; p2 =&gt; p3 ; _ =&gt; p4} ;
    prevPrec : Prec =&gt; Prec =
      table {p4 =&gt; p3 ; p3 =&gt; p2 ; p2 =&gt; p1 ; _ =&gt; p0} ;

    mkPrec : Str -&gt; Prec =&gt; Prec =&gt; Str = \str -&gt;
      table {
        p4 =&gt; table {                -- use the term of precedence p4...
          _   =&gt; str} ;              -- ...always without parentheses
        p3 =&gt; table {                -- use the term of precedence p3...
          p4  =&gt; mkParenth str ;     -- ...in parentheses if p4 is required...
          _   =&gt; str} ;              -- ...otherwise without parentheses
        p2 =&gt; table {
          p4  =&gt; mkParenth str ;
          p3  =&gt; mkParenth str ;
          _   =&gt; str} ;
        p1 =&gt; table {
          p1  =&gt; str ;
          p0  =&gt; str ;
          _   =&gt; mkParenth str} ;
        p0 =&gt; table {
          p0  =&gt; str ;
          _   =&gt; mkParenth str}
            } ;
</PRE>
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<P>
make a string into a constant, of precedence p4
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<PRE>
    mkConst : Str -&gt; PrecTerm =
      \f -&gt;
      mkPrec f ! p4 ;
</PRE>
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<P>
make a string into a 1/2/3 -place prefix operator, of precedence p3
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<PRE>
    mkFun1 : Str -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \x -&gt;
      table {k =&gt; mkPrec (f ++ x ! p4) ! p3 ! k} ;
    mkFun2 : Str -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \x -&gt; \y -&gt;
      table {k =&gt; mkPrec (f ++ x ! p4 ++ y ! p4) ! p3 ! k} ;
    mkFun3 : Str -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \x -&gt; \y -&gt; \z -&gt;
      table {k =&gt; mkPrec (f ++ x ! p4 ++ y ! p4 ++ z ! p4) ! p3 ! k} ;
</PRE>
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<P>
make a string into a non/left/right -associative infix operator, of precedence p
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<PRE>
    mkInfix : Str -&gt; Prec -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      table {k =&gt; mkPrec (x ! (nextPrec ! p) ++ f ++ y ! (nextPrec ! p)) ! p ! k} ;
    mkInfixL : Str -&gt; Prec -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      table {k =&gt; mkPrec (x ! p ++ f ++ y ! (nextPrec ! p)) ! p ! k} ;
    mkInfixR : Str -&gt; Prec -&gt; PrecTerm -&gt; PrecTerm -&gt; PrecTerm =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      table {k =&gt; mkPrec (x ! (nextPrec ! p) ++ f ++ y ! p) ! p ! k} ;
</PRE>
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<P>
alternative:
precedence as inherent feature
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<PRE>
    lintype TermWithPrec = {s : Str ; p : Prec} ;

    oper
    mkpPrec : Str -&gt; Prec -&gt; TermWithPrec =
      \f -&gt; \p -&gt;
      {s = f ; p = p} ;

    usePrec : TermWithPrec -&gt; Prec -&gt; Str =
      \x -&gt; \p -&gt;
      mkPrec x.s ! x.p ! p ;
</PRE>
<P></P>
<P>
make a string into a constant, of precedence p4
</P>
<PRE>
    mkpConst : Str -&gt; TermWithPrec =
      \f -&gt;
      mkpPrec f p4 ;
</PRE>
<P></P>
<P>
make a string into a 1/2/3 -place prefix operator, of precedence p3
</P>
<PRE>
    mkpFun1 : Str -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \x -&gt;
      mkpPrec (f ++ usePrec x p4) p3 ;

    mkpFun2 : Str -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \x -&gt; \y -&gt;
      mkpPrec (f ++ usePrec x p4 ++ usePrec y p4) p3 ;

    mkpFun3 : Str -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \x -&gt; \y -&gt; \z -&gt;
      mkpPrec (f ++ usePrec x p4 ++ usePrec y p4 ++ usePrec z p4) p3 ;
</PRE>
<P></P>
<P>
make a string a into non/left/right -associative infix operator, of precedence p
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<PRE>
    mkpInfix : Str -&gt; Prec -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      mkpPrec (usePrec x (nextPrec ! p) ++ f ++ usePrec y (nextPrec ! p)) p ;
    mkpInfixL : Str -&gt; Prec -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      mkpPrec (usePrec x p ++ f ++ usePrec y (nextPrec ! p)) p ;
    mkpInfixR : Str -&gt; Prec -&gt; TermWithPrec -&gt; TermWithPrec -&gt; TermWithPrec =
      \f -&gt; \p -&gt; \x -&gt; \y -&gt;
      mkpPrec (usePrec x (nextPrec ! p) ++ f ++ usePrec y p) p ;
    } ;
</PRE>
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