literals of rational number, e.g. 1.2(3), are now supported and are evaluated as fractions

operand-const.go

@@ -27,6 +27,7 @@ func init() {
 	registerTermConstructor(SymString, newConstTerm)
 	registerTermConstructor(SymInteger, newConstTerm)
 	registerTermConstructor(SymFloat, newConstTerm)
+	registerTermConstructor(SymFraction, newConstTerm)
 	registerTermConstructor(SymBool, newConstTerm)
 	registerTermConstructor(SymKwNil, newConstTerm)
 }

scanner.go

@@ -385,7 +385,8 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 				}
 			}
 		}
-		if err == nil && (ch == 'e' || ch == 'E') {
+		if err == nil {
+			if ch == 'e' || ch == 'E' {
 				sym = SymFloat
 				sb.WriteByte(ch)
 				if ch, err = self.readChar(); err == nil {
@@ -398,7 +399,21 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 							sb.WriteByte(ch)
 						}
 					} else {
-					err = errors.New("expected integer exponent")
+						err = fmt.Errorf("[%d:%d] expected integer exponent, got %c", self.row, self.column, ch)
+					}
+				}
+			} else if ch == '(' {
+				sym = SymFraction
+				ch, err = self.readChar()
+				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = self.readChar() {
+					sb.WriteByte(ch)
+				}
+				if err == nil {
+					if ch != ')' {
+						err = fmt.Errorf("[%d:%d] expected ')', got '%c'", self.row, self.column, ch)
+					} else {
+						_, err = self.readChar()
+					}
 				}
 			}
 		}
@@ -412,6 +427,8 @@ func (self *scanner) parseNumber(firstCh byte) (tk *Token) {
 		txt := sb.String()
 		if sym == SymFloat {
 			value, err = strconv.ParseFloat(txt, 64)
+		} else if sym == SymFraction {
+			value, err = makeGeneratingFraction(txt)
 		} else {
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}

symbol.go

@@ -73,6 +73,7 @@ const (
 	SymBool
 	SymInteger
 	SymFloat
+	SymFraction
 	SymString
 	SymIterator
 	SymOr