forked from GitHub/gf-core
55 lines
1.5 KiB
Plaintext
55 lines
1.5 KiB
Plaintext
resource Formal = open Prelude in {
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-- to replace the old library Precedence
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oper
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Prec : PType ;
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TermPrec : Type = {s : Str ; p : Prec} ;
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mkPrec : Prec -> Str -> TermPrec = \p,s ->
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{s = s ; p = p} ;
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top : TermPrec -> Str = usePrec 0 ;
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constant : Str -> TermPrec = mkPrec highest ;
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infixl : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
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mkPrec p (usePrec p x ++ f ++ usePrec (nextPrec p) y) ;
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infixr : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
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mkPrec p (usePrec (nextPrec p) x ++ f ++ usePrec p y) ;
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infixn : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
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mkPrec p (usePrec (nextPrec p) x ++ f ++ usePrec (nextPrec p) y) ;
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-- auxiliaries, should not be needed so much
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usePrec : Prec -> TermPrec -> Str = \p,x ->
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case lessPrec x.p p of {
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True => parenth x.s ;
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False => parenthOpt x.s
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} ;
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parenth : Str -> Str = \s -> "(" ++ s ++ ")" ;
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parenthOpt : Str -> Str = \s -> variants {s ; "(" ++ s ++ ")"} ;
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--.
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-- low-level things: don't use
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Prec : PType = Predef.Ints 4 ;
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highest = 4 ;
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lessPrec : Prec -> Prec -> Bool = \p,q ->
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case <<p,q> : Prec * Prec> of {
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<3,4> | <2,3> | <2,4> => True ;
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<1,1> | <1,0> | <0,0> => False ;
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<1,_> | <0,_> => True ;
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_ => False
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} ;
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nextPrec : Prec -> Prec = \p -> case <p : Prec> of {
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4 => 4 ;
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n => Predef.plus n 1
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} ;
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}
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