@@ -20,6 +20,9 @@ import scala.language.implicitConversions
2020
2121// TODO: better error handling (labelling like parsec's <?>)
2222
23+ /** An enumeration of operator associativity values: `Left`, `Right`, and
24+ * `Non`.
25+ */
2326object Associativity extends Enumeration {
2427type Associativity = Value
2528
@@ -1025,18 +1028,34 @@ trait Parsers {
10251028
10261029import Associativity ._
10271030
1028- class PrecedenceParser [Exp ,Op ](primary :Parser [Exp ],
1029- binop :Parser [Op ],
1030- precedence :Op => Int ,
1031- associativity :Op => Associativity ,
1032- makeBinop : (Exp ,Op ,Exp )=> Exp )extends Parser [Exp ] {
1033- class PrecedenceSuffixParser (lhs :Exp ,minLevel :Int )extends Parser [Exp ] {
1031+ /** A parser that respects operator the precedence and associativity
1032+ * conventions specified in its constructor.
1033+ *
1034+ *@param primary a parser that matches atomic expressions (the atomicity is
1035+ * from the perspective of binary operators). May include
1036+ * unary operators or parentheses.
1037+ *@param binop a parser that matches binary operators.
1038+ *@param precedence a function from operators to their precedence levels.
1039+ * Operators with higher precedence values bind more
1040+ * tightly than those with lower values.
1041+ *@param associativity a function from operators to their associativity.
1042+ *@param makeBinop a function that combines two operands and an operator
1043+ * into a new expression. The result must have the same type
1044+ * as the operands because intermediate results become
1045+ * operands to other operators.
1046+ */
1047+ class PrecedenceParser [Exp ,Op ,E <: Exp ](primary :Parser [E ],
1048+ binop :Parser [Op ],
1049+ precedence :Op => Int ,
1050+ associativity :Op => Associativity ,
1051+ makeBinop : (Exp ,Op ,Exp )=> Exp )extends Parser [Exp ] {
1052+ private class ExpandLeftParser (lhs :Exp ,minLevel :Int )extends Parser [Exp ] {
10341053val opPrimary = binop~ primary;
1035- def parse (input :Input ): ParseResult [Exp ]= {
1054+ def apply (input :Input ): ParseResult [Exp ]= {
10361055 opPrimary(input)match {
10371056case Success (op~ rhs, next)if precedence(op)>= minLevel=> {
1038- new PrecedenceRhsSuffixParser (rhs, precedence(op), minLevel)(next)match {
1039- case Success (r, nextInput)=> new PrecedenceSuffixParser (makeBinop(lhs, op, r), minLevel)(nextInput);
1057+ new ExpandRightParser (rhs, precedence(op), minLevel)(next)match {
1058+ case Success (r, nextInput)=> new ExpandLeftParser (makeBinop(lhs, op, r), minLevel)(nextInput);
10401059case ns=> ns// dead code
10411060 }
10421061 }
@@ -1047,7 +1066,7 @@ trait Parsers {
10471066 }
10481067 }
10491068
1050- class PrecedenceRhsSuffixParser (rhs :Exp ,currentLevel :Int ,minLevel :Int )extends Parser [Exp ] {
1069+ private class ExpandRightParser (rhs :Exp ,currentLevel :Int ,minLevel :Int )extends Parser [Exp ] {
10511070private def nextLevel (nextBinop :Op ): Option [Int ]= {
10521071if (precedence(nextBinop)> currentLevel) {
10531072Some (minLevel+ 1 )
@@ -1057,14 +1076,14 @@ trait Parsers {
10571076None
10581077 }
10591078 }
1060- def parse (input :Input ): ParseResult [Exp ]= {
1079+ def apply (input :Input ): ParseResult [Exp ]= {
10611080def done : ParseResult [Exp ]= Success (rhs, input)
10621081 binop(input)match {
10631082case Success (nextBinop,_)=> {
10641083 nextLevel(nextBinop)match {
10651084case Some (level)=> {
1066- new PrecedenceSuffixParser (rhs, level)(input)match {
1067- case Success (r, next)=> new PrecedenceRhsSuffixParser (r, currentLevel, minLevel)(next)
1085+ new ExpandLeftParser (rhs, level)(input)match {
1086+ case Success (r, next)=> new ExpandRightParser (r, currentLevel, minLevel)(next)
10681087case ns=> ns// dead code
10691088 }
10701089 }
@@ -1076,10 +1095,12 @@ trait Parsers {
10761095 }
10771096 }
10781097
1079- def parse (input :Input ): ParseResult [Exp ]= {
1098+ /** Parse an expression.
1099+ */
1100+ def apply (input :Input ): ParseResult [Exp ]= {
10801101 primary(input)match {
10811102case Success (lhs, next)=> {
1082- new PrecedenceSuffixParser (lhs,0 )(next)
1103+ new ExpandLeftParser (lhs,0 )(next)
10831104 }
10841105case noSuccess=> noSuccess
10851106 }