feat: ad support for error value

Author: link-duan

ast.go

@@ -28,6 +28,7 @@ const (
 	Number
 	String
 	BoolLiteral        // TRUE or FALSE
+	EValue             // Error value (e.g., #DIV/0!, #VALUE!, etc)
 	Exclamation        // !
 	BraceOpen          // {
 	BraceClose         // }

lexer.go

@@ -116,6 +116,8 @@ func (l *lexer) next() (*Token, error) {
 		default:
 			return newToken(start, l.pos, GreaterThan, ">"), nil
 		}
+	case '#':
+		return l.errValue()
 	default:
 		if isDigit(l.ch) {
 			return l.number()
@@ -150,6 +152,12 @@ func (l *lexer) nextch() {
 	}
 }
 
+func (l *lexer) eat(n int) {
+	for i := 0; i < n; i++ {
+		l.nextch()
+	}
+}
+
 func (l *lexer) absoluteReference() (*Token, error) {
 	var start = l.pos
 	var startOffset = l.offset - 1 // Start at the current character
@@ -205,6 +213,33 @@ func (l *lexer) absoluteReference() (*Token, error) {
 	return nil, newLexError(l.pos, "invalid absolute reference after '$'")
 }
 
+func (l *lexer) errValue() (*Token, error) {
+	var values = []string{
+		"#NULL!",
+		"#DIV/0!",
+		"#VALUE!",
+		"#REF!",
+		"#NAME?",
+		"#NUM!",
+		"#N/A",
+	}
+	for _, value := range values {
+		// check length
+		if l.offset-1+len(value) > len(l.src) {
+			continue // Not enough characters left for this error value
+		}
+		if string(l.src[l.offset-1:l.offset-1+len(value)]) == value {
+			var start = l.pos
+			l.eat(len(value) - 1) // Consume the error value
+			var end = l.pos
+			l.offset += len(value) - 1 // Adjust offset to skip the error value
+			l.ch = l.peekChar()        // Update current character
+			return newToken(start, end, EValue, value), nil
+		}
+	}
+	return nil, newLexError(l.pos, "unrecognized error value")
+}
+
 func (l *lexer) stringLiteral(quote rune) (*Token, error) {
 	var start = l.pos
 	var end = start

lexer_test.go

@@ -10,6 +10,9 @@ func TestLexer(t *testing.T) {
 		src      string
 		expected TokenType
 	}{
+		{"#DIV/0!", EValue},
+		{"#VALUE!", EValue},
+		{"#N/A", EValue},
 		{"A$123", Cell},
 		{"$A$1", Cell},
 		{"A1", Cell},