Change semantic action APIs

The driver reports whether it recovered from an error to the semantic action APIs via the argument `recovered`.

driver/parser.go

@@ -85,20 +85,22 @@ ACTION_LOOP:
 		case act < 0: // Shift
 			nextState := act * -1
 
+			recovered := false
 			if p.onError {
+				p.shiftCount++
+
 				// When the parser performs shift three times, the parser recovers from the error state.
-				if p.shiftCount < 3 {
-					p.shiftCount++
-				} else {
+				if p.shiftCount >= 3 {
 					p.onError = false
 					p.shiftCount = 0
+					recovered = true
 				}
 			}
 
 			p.shift(nextState)
 
 			if p.semAct != nil {
-				p.semAct.Shift(tok)
+				p.semAct.Shift(tok, recovered)
 			}
 
 			tok, err = p.nextToken()
@@ -108,9 +110,11 @@ ACTION_LOOP:
 		case act > 0: // Reduce
 			prodNum := act
 
+			recovered := false
 			if p.onError && p.gram.ParsingTable.RecoverProductions[prodNum] != 0 {
 				p.onError = false
 				p.shiftCount = 0
+				recovered = true
 			}
 
 			accepted := p.reduce(prodNum)
@@ -123,7 +127,7 @@ ACTION_LOOP:
 			}
 
 			if p.semAct != nil {
-				p.semAct.Reduce(prodNum)
+				p.semAct.Reduce(prodNum, recovered)
 			}
 		default: // Error
 			if p.onError {

driver/semantic_action.go

@@ -10,17 +10,18 @@ import (
 
 type SemanticActionSet interface {
 	// Shift runs when the driver shifts a symbol onto the state stack. `tok` is a token corresponding to
-	// the symbol.
-	Shift(tok *mldriver.Token)
+	// the symbol. When the driver recovered from an error state by shifting the token, `recovered` is true.
+	Shift(tok *mldriver.Token, recovered bool)
 
 	// Shift runs when the driver shifts a symbol onto the state stack. `tok` is a token corresponding to
 	// the symbol. This function doesn't take a token as an argument because a token corresponding to
 	// the error symbol doesn't exist.
 	ShiftError()
 
 	// Reduce runs when the driver reduces an RHS of a production to its LHS. `prodNum` is a number of
-	// the production.
-	Reduce(prodNum int)
+	// the production. When the driver recovered from an error state by reducing the production,
+	// `recovered` is true.
+	Reduce(prodNum int, recovered bool)
 
 	// Accept runs when the driver accepts an input.
 	Accept()
@@ -96,7 +97,7 @@ func NewSyntaxTreeActionSet(gram *spec.CompiledGrammar, makeAST bool, makeCST bo
 	}
 }
 
-func (a *SyntaxTreeActionSet) Shift(tok *mldriver.Token) {
+func (a *SyntaxTreeActionSet) Shift(tok *mldriver.Token, recovered bool) {
 	term := a.tokenToTerminal(tok)
 
 	var ast *Node
@@ -146,7 +147,7 @@ func (a *SyntaxTreeActionSet) ShiftError() {
 	})
 }
 
-func (a *SyntaxTreeActionSet) Reduce(prodNum int) {
+func (a *SyntaxTreeActionSet) Reduce(prodNum int, recovered bool) {
 	lhs := a.gram.ParsingTable.LHSSymbols[prodNum]
 
 	// When an alternative is empty, `n` will be 0, and `handle` will be empty slice.

driver/semantic_action_test.go

@@ -15,18 +15,26 @@ type testSemAct struct {
 	actLog []string
 }
 
-func (a *testSemAct) Shift(tok *mldriver.Token) {
-	a.actLog = append(a.actLog, fmt.Sprintf("shift/%v", tok.KindName))
+func (a *testSemAct) Shift(tok *mldriver.Token, recovered bool) {
+	if recovered {
+		a.actLog = append(a.actLog, fmt.Sprintf("shift/%v/recovered", tok.KindName))
+	} else {
+		a.actLog = append(a.actLog, fmt.Sprintf("shift/%v", tok.KindName))
+	}
 }
 
 func (a *testSemAct) ShiftError() {
 	a.actLog = append(a.actLog, "shift/error")
 }
 
-func (a *testSemAct) Reduce(prodNum int) {
+func (a *testSemAct) Reduce(prodNum int, recovered bool) {
 	lhsSym := a.gram.ParsingTable.LHSSymbols[prodNum]
 	lhsText := a.gram.ParsingTable.NonTerminals[lhsSym]
-	a.actLog = append(a.actLog, fmt.Sprintf("reduce/%v", lhsText))
+	if recovered {
+		a.actLog = append(a.actLog, fmt.Sprintf("reduce/%v/recovered", lhsText))
+	} else {
+		a.actLog = append(a.actLog, fmt.Sprintf("reduce/%v", lhsText))
+	}
 }
 
 func (a *testSemAct) Accept() {
@@ -46,6 +54,7 @@ func TestParserWithSemanticAction(t *testing.T) {
 seq
     : seq elem semicolon
 	| elem semicolon
+    | error star star semicolon
 	| error semicolon #recover
 	;
 elem
@@ -54,6 +63,7 @@ elem
 
 ws: "[\u{0009}\u{0020}]+" #skip;
 semicolon: ';';
+star: '*';
 char: "[a-z]";
 `
 
@@ -102,25 +112,34 @@ char: "[a-z]";
 		{
 			caption: "when a grammar has `error` symbol, the driver calls `TrapError` and `ShiftError`.",
 			specSrc: specSrcWithErrorProd,
-			src:     `a; b !; c d !; e f g;`,
+			src:     `a; b !; c d !; e ! * *; h i j;`,
 			actLog: []string{
 				"shift/char",
 				"trap/1",
 				"shift/error",
 				"shift/semicolon",
-				"reduce/seq",
+				"reduce/seq/recovered",
 
 				"shift/char",
 				"trap/2",
 				"shift/error",
 				"shift/semicolon",
-				"reduce/seq",
+				"reduce/seq/recovered",
 
 				"shift/char",
 				"shift/char",
 				"trap/3",
 				"shift/error",
 				"shift/semicolon",
+				"reduce/seq/recovered",
+
+				"shift/char",
+				"trap/2",
+				"shift/error",
+				"shift/star",
+				"shift/star",
+				// When the driver shifts three times, it recovers from an error.
+				"shift/semicolon/recovered",
 				"reduce/seq",
 
 				"shift/char",