@@ -1056,24 +1056,34 @@ trait Parsers {
10561056 * from the perspective of binary operators). May include
10571057 * unary operators or parentheses.
10581058 *@param binop a parser that matches binary operators.
1059- *@param precedence afunction from operators to their precedence levels.
1060- *Operators with higher precedence values bind more
1061- *tightly than those with lower values.
1062- *@param associativity a function from operators to their associativity .
1059+ *@param prec_table alist of tuples, each of which encodes a level of
1060+ *precedence. Precedence is encoded highest to lowest.
1061+ *Each precedence level contains an Associativity value
1062+ * and a list of operators .
10631063 *@param makeBinop a function that combines two operands and an operator
10641064 * into a new expression. The result must have the same type
10651065 * as the operands because intermediate results become
10661066 * operands to other operators.
10671067*/
10681068class PrecedenceParser [Exp ,Op ,E <: Exp ](primary :Parser [E ],
10691069binop :Parser [Op ],
1070- precedence :Op => Int ,
1071- associativity :Op => Associativity ,
1070+ prec_table :List [(Associativity ,List [Op ])],
10721071makeBinop : (Exp ,Op ,Exp )=> Exp )extends Parser [Exp ] {
1072+ private def decodePrecedence : (Map [Op ,Int ],Map [Op ,Associativity ])= {
1073+ var precedence = Map .empty[Op ,Int ]
1074+ var associativity = Map .empty[Op ,Associativity ]
1075+ var level = prec_table.length
1076+ for ((assoc, ops)<- prec_table) {
1077+ precedence= precedence++ (for (op<- ops)yield (op, level))
1078+ associativity= associativity++ (for (op<- ops)yield (op, assoc))
1079+ level-= 1
1080+ }
1081+ (precedence, associativity)
1082+ }
1083+ val (precedence, associativity)= decodePrecedence
10731084private class ExpandLeftParser (lhs :Exp ,minLevel :Int )extends Parser [Exp ] {
1074- val opPrimary = binop~ primary;
10751085def apply (input :Input ): ParseResult [Exp ]= {
1076- opPrimary (input)match {
1086+ (binop ~ primary) (input)match {
10771087case Success (op~ rhs, next)if precedence(op)>= minLevel=> {
10781088new ExpandRightParser (rhs, precedence(op), minLevel)(next)match {
10791089case Success (r, nextInput)=> new ExpandLeftParser (makeBinop(lhs, op, r), minLevel)(nextInput);