- replaced recursive parsing of binary expressions with
precedence-based expression parser
SVN=126556
diff --git a/usr/gri/src/parser.go b/usr/gri/src/parser.go
index 355120d..e811fc8 100644
--- a/usr/gri/src/parser.go
+++ b/usr/gri/src/parser.go
@@ -20,7 +20,7 @@
func (P *Parser) PrintIndent() {
for i := P.indent; i > 0; i-- {
- print " ";
+ print ". ";
}
}
@@ -556,6 +556,7 @@
P.Trace("GoStat");
P.Expect(Scanner.GO);
P.ParseExpression();
+ P.Ecart();
}
@@ -755,6 +756,8 @@
func (P *Parser) TryStatement() bool {
P.Trace("Statement (try)");
+ indent := P.indent;
+ res := true;
switch P.tok {
case Scanner.CONST: fallthrough;
case Scanner.TYPE: fallthrough;
@@ -790,11 +793,13 @@
P.ParseSelectStat();
default:
// no statement found
- P.Ecart();
- return false;
+ res = false;
+ }
+ if indent != P.indent {
+ panic "imbalanced tracing code"
}
P.Ecart();
- return true;
+ return res;
}
@@ -856,6 +861,7 @@
func (P *Parser) ParseDeclaration() {
P.Trace("Declaration");
+ indent := P.indent;
switch P.tok {
case Scanner.CONST:
P.ParseConstDecl();
@@ -870,6 +876,9 @@
default:
P.Error("declaration expected");
}
+ if indent != P.indent {
+ panic "imbalanced tracing code"
+ }
P.Ecart();
}
@@ -907,7 +916,7 @@
case Scanner.NEW:
P.ParseNew();
default:
- panic "unknown operand"
+ P.Error("operand expected");
}
P.Ecart();
}
@@ -992,90 +1001,44 @@
}
-func (P *Parser) ParseMultiplicativeExpr() {
- P.Trace("MultiplicativeExpr");
+func Precedence(tok int) int {
+ // TODO should use a map or array here for lookup
+ switch tok {
+ case Scanner.COR:
+ return 1;
+ case Scanner.CAND:
+ return 2;
+ case Scanner.EQL, Scanner.NEQ, Scanner.LSS, Scanner.LEQ, Scanner.GTR, Scanner.GEQ:
+ return 3;
+ case Scanner.ADD, Scanner.SUB, Scanner.OR, Scanner.XOR:
+ return 4;
+ case Scanner.MUL, Scanner.QUO, Scanner.REM, Scanner.SHL, Scanner.SHR, Scanner.AND:
+ return 5;
+ }
+ return 0;
+}
+
+
+func (P *Parser) ParseBinaryExpr(prec1 int) {
+ P.Trace("BinaryExpr");
P.ParseUnaryExpr();
- for {
- switch P.tok {
- case Scanner.MUL: fallthrough;
- case Scanner.QUO: fallthrough;
- case Scanner.REM: fallthrough;
- case Scanner.SHL: fallthrough;
- case Scanner.SHR: fallthrough;
- case Scanner.AND:
+ for prec := Precedence(P.tok); prec >= prec1; prec-- {
+ for Precedence(P.tok) == prec {
P.Next();
- P.ParseUnaryExpr();
- default:
- P.Ecart();
- return;
+ P.ParseBinaryExpr(prec + 1);
}
}
P.Ecart();
}
-func (P *Parser) ParseAdditiveExpr() {
- P.Trace("AdditiveExpr");
- P.ParseMultiplicativeExpr();
- for {
- switch P.tok {
- case Scanner.ADD: fallthrough;
- case Scanner.SUB: fallthrough;
- case Scanner.OR: fallthrough;
- case Scanner.XOR:
- P.Next();
- P.ParseMultiplicativeExpr();
- default:
- P.Ecart();
- return;
- }
- }
- P.Ecart();
-}
-
-
-func (P *Parser) ParseRelationalExpr() {
- P.Trace("RelationalExpr");
- P.ParseAdditiveExpr();
- switch P.tok {
- case Scanner.EQL: fallthrough;
- case Scanner.NEQ: fallthrough;
- case Scanner.LSS: fallthrough;
- case Scanner.LEQ: fallthrough;
- case Scanner.GTR: fallthrough;
- case Scanner.GEQ:
- P.Next();
- P.ParseAdditiveExpr();
- }
- P.Ecart();
-}
-
-
-func (P *Parser) ParseLANDExpr() {
- P.Trace("LANDExpr");
- P.ParseRelationalExpr();
- for P.tok == Scanner.CAND {
- P.Next();
- P.ParseRelationalExpr();
- }
- P.Ecart();
-}
-
-
-func (P *Parser) ParseLORExpr() {
- P.Trace("LORExpr");
- P.ParseLANDExpr();
- for P.tok == Scanner.COR {
- P.Next();
- P.ParseLANDExpr();
- }
- P.Ecart();
-}
-
-
func (P *Parser) ParseExpression() {
P.Trace("Expression");
- P.ParseLORExpr();
+ indent := P.indent;
+ P.ParseBinaryExpr(1);
+ if indent != P.indent {
+ panic "imbalanced tracing code";
+ }
P.Ecart();
}
