Add label notation

2 files changed, 25 insertions, 0 deletions

diff --git a/grammar/grammar.go b/grammar/grammar.go
index 9d1933b..3f1117c 100644
--- a/grammar/grammar.go
+++ b/grammar/grammar.go
@@ -677,6 +677,7 @@ func (b *GrammarBuilder) genProductionsAndActions(root *spec.RootNode, symTabAnd
 	LOOP_RHS:
 		for _, alt := range prod.RHS {
 			altSyms := make([]symbol, len(alt.Elements))
+			labels := map[string]int{}
 			for i, elem := range alt.Elements {
 				var sym symbol
 				if elem.Pattern != "" {
@@ -707,6 +708,28 @@ func (b *GrammarBuilder) genProductionsAndActions(root *spec.RootNode, symTabAnd
 					}
 				}
 				altSyms[i] = sym
+
+				if elem.Label != nil {
+					if _, added := labels[elem.Label.Name]; added {
+						b.errs = append(b.errs, &verr.SpecError{
+							Cause:  semErrDuplicateLabel,
+							Detail: elem.Label.Name,
+							Row:    elem.Label.Pos.Row,
+							Col:    elem.Label.Pos.Col,
+						})
+						continue LOOP_RHS
+					}
+					if _, found := symTab.toSymbol(elem.Label.Name); found {
+						b.errs = append(b.errs, &verr.SpecError{
+							Cause:  semErrInvalidLabel,
+							Detail: elem.Label.Name,
+							Row:    elem.Label.Pos.Row,
+							Col:    elem.Label.Pos.Col,
+						})
+						continue LOOP_RHS
+					}
+					labels[elem.Label.Name] = i
+				}
 			}
 
 			p, err := newProduction(lhsSym, altSyms)
diff --git a/grammar/semantic_error.go b/grammar/semantic_error.go
index d540c03..4326d81 100644
--- a/grammar/semantic_error.go
+++ b/grammar/semantic_error.go
@@ -27,6 +27,8 @@ var (
 	semErrDuplicateTerminal   = newSemanticError("duplicate terminal")
 	semErrDuplicateName       = newSemanticError("duplicate names are not allowed between terminals and non-terminals")
 	semErrErrSymIsReserved    = newSemanticError("symbol 'error' is reserved as a terminal symbol")
+	semErrDuplicateLabel      = newSemanticError("a label must be unique in an alternative")
+	semErrInvalidLabel        = newSemanticError("a label must differ from terminal symbols or non-terminal symbols")
 	semErrDirInvalidName      = newSemanticError("invalid directive name")
 	semErrDirInvalidParam     = newSemanticError("invalid parameter")
 )