diff --git a/parser.go b/parser.go
index 48c9dcd..90897e0 100644
--- a/parser.go
+++ b/parser.go
@@ -191,10 +191,11 @@ func (self *parser) Parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, e
 func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef bool, termSymbols ...Symbol) (tree *ast, err error) {
 	var selectorTerm *term = nil
 	var currentTerm *term = nil
+	var tk *Token
 	tree = NewAst()
 	firstToken := true
 	lastSym := SymUnknown
-	for tk := scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); tk = scanner.Next() {
+	for tk = scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); tk = scanner.Next() {
 		if tk.Sym == SymComment {
 			continue
 		}
@@ -281,6 +282,9 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 		}
 		lastSym = tk.Sym
 	}
+	if err == nil {
+		err = tk.Error()
+	}
 	return
 }
 
diff --git a/scanner.go b/scanner.go
index e4eb848..aaa24af 100644
--- a/scanner.go
+++ b/scanner.go
@@ -280,62 +280,116 @@ func (self *scanner) sync(err error) error {
 	return err
 }
 
+func isBinaryDigit(ch byte) bool {
+	return ch == '0' || ch == '1'
+}
+
+func isOctalDigit(ch byte) bool {
+	return ch >= '0' && ch <= '7'
+}
+
+func isDecimalDigit(ch byte) bool {
+	return ch >= '0' && ch <= '9'
+}
+
+func isHexDigit(ch byte) bool {
+	return (ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')
+}
+
+func (self *scanner) initBase(sb *strings.Builder, currentFirstCh byte) (firstCh byte, numBase int, digitFunc func(byte) bool, err error) {
+	var ch byte
+	var digitType string
+	firstCh = currentFirstCh
+	digitFunc = isDecimalDigit
+	numBase = 10
+
+	if ch, err = self.peek(); err == nil {
+		if ch == 'b' || ch == 'B' {
+			numBase = 2
+			digitType = "binary"
+			self.readChar()
+			digitFunc = isBinaryDigit
+			firstCh, err = self.readChar()
+		} else if ch == 'o' || ch == 'O' {
+			numBase = 8
+			digitType = "octal"
+			self.readChar()
+			digitFunc = isOctalDigit
+			firstCh, err = self.readChar()
+		} else if ch == 'x' || ch == 'X' {
+			numBase = 16
+			digitType = "hex"
+			self.readChar()
+			digitFunc = isHexDigit
+			firstCh, err = self.readChar()
+		}
+		if err == nil && !digitFunc(firstCh) {
+			if len(digitType) == 0 {
+				digitType = "decimal"
+			}
+			err = fmt.Errorf("expected %s digit, got '%c'", digitType, firstCh)
+		}
+	} else if err == io.EOF {
+		err = nil
+	}
+	return
+}
+
 func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sym Symbol = SymInteger
-	var value any
 	var sb strings.Builder
+	var isDigit func(byte) bool = isDecimalDigit
+	var numBase = 10
 
-	for ch = firstCh; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+	if firstCh == '0' {
+		firstCh, numBase, isDigit, err = self.initBase(&sb, firstCh)
+	}
+	for ch = firstCh; err == nil && isDigit(ch); ch, err = self.readChar() {
 		sb.WriteByte(ch)
 	}
-	if ch == '.' {
-		sym = SymFloat
-		sb.WriteByte(ch)
-		ch, err = self.readChar()
-		if ch >= '0' && ch <= '9' {
-			for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
-				sb.WriteByte(ch)
-			}
-		}
-	}
-	if ch == 'e' || ch == 'E' {
-		sym = SymFloat
-		sb.WriteByte(ch)
-		if ch, err = self.readChar(); err == nil {
-			if ch == '+' || ch == '-' {
-				sb.WriteByte(ch)
-				ch, err = self.readChar()
-			}
+
+	if numBase == 10 {
+		if err == nil && ch == '.' {
+			sym = SymFloat
+			sb.WriteByte(ch)
+			ch, err = self.readChar()
 			if ch >= '0' && ch <= '9' {
 				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
 					sb.WriteByte(ch)
 				}
-				//err = self.sync(err)
-			} else {
-				err = errors.New("expected integer exponent")
 			}
 		}
-		// } else {
-		// err = self.sync(err)
+		if err == nil && (ch == 'e' || ch == 'E') {
+			sym = SymFloat
+			sb.WriteByte(ch)
+			if ch, err = self.readChar(); err == nil {
+				if ch == '+' || ch == '-' {
+					sb.WriteByte(ch)
+					ch, err = self.readChar()
+				}
+				if ch >= '0' && ch <= '9' {
+					for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+						sb.WriteByte(ch)
+					}
+				} else {
+					err = errors.New("expected integer exponent")
+				}
+			}
+		}
 	}
 
 	if err != nil && err != io.EOF {
 		tk = self.makeErrorToken(err)
 	} else {
+		var value any
 		err = self.sync(err)
 		txt := sb.String()
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
-		} else if strings.HasPrefix(txt, "0x") {
-			value, err = strconv.ParseInt(txt, 16, 64)
-		} else if strings.HasPrefix(txt, "0o") {
-			value, err = strconv.ParseInt(txt, 8, 64)
-		} else if strings.HasPrefix(txt, "0b") {
-			value, err = strconv.ParseInt(txt, 2, 64)
 		} else {
-			value, err = strconv.ParseInt(txt, 10, 64)
+			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
 		if err == nil {
 			tk = self.makeValueToken(sym, txt, value)
diff --git a/token.go b/token.go
index 76f6bba..c515e35 100644
--- a/token.go
+++ b/token.go
@@ -67,3 +67,17 @@ func (self *Token) Errorf(template string, args ...any) (err error) {
 	err = fmt.Errorf(fmt.Sprintf("[%d:%d] ", self.row, self.col)+template, args...)
 	return
 }
+
+func (self *Token) Error() (err error) {
+	if self.Sym == SymError {
+		if msg, ok := self.Value.(error); ok {
+			err = fmt.Errorf("[%d:%d] %v", self.row, self.col, msg)
+		}
+	}
+	return
+}
+
+func (self *Token) Errors(msg string) (err error) {
+	err = fmt.Errorf("[%d:%d] %v", self.row, self.col, msg)
+	return
+}