diff --git a/src/Pure/ML/ml_syntax.scala b/src/Pure/ML/ml_syntax.scala
--- a/src/Pure/ML/ml_syntax.scala
+++ b/src/Pure/ML/ml_syntax.scala
@@ -1,65 +1,66 @@
 /*  Title:      Pure/ML/ml_syntax.scala
     Author:     Makarius
 
 Concrete ML syntax for basic values.
 */
 
 package isabelle
 
 
 object ML_Syntax
 {
-  /* int */
+  /* numbers */
 
-  private def signed_int(s: String): String =
+  private def signed(s: String): String =
     if (s(0) == '-') "~" + s.substring(1) else s
 
-  def print_int(i: Int): String = signed_int(Value.Int(i))
-  def print_long(i: Long): String = signed_int(Value.Long(i))
+  def print_int(x: Int): String = signed(Value.Int(x))
+  def print_long(x: Long): String = signed(Value.Long(x))
+  def print_double(x: Double): String = signed(Value.Double(x))
 
 
   /* string */
 
   private def print_byte(c: Byte): String =
     c match {
       case 34 => "\\\""
       case 92 => "\\\\"
       case 9 => "\\t"
       case 10 => "\\n"
       case 12 => "\\f"
       case 13 => "\\r"
       case _ =>
         if (c < 0) "\\" + Library.signed_string_of_int(256 + c)
         else if (c < 32) new String(Array[Char](92, 94, (c + 64).toChar))
         else if (c < 127) Symbol.ascii(c.toChar)
         else "\\" + Library.signed_string_of_int(c)
     }
 
   private def print_symbol(s: Symbol.Symbol): String =
     if (s.startsWith("\\<")) s
     else UTF8.bytes(s).iterator.map(print_byte).mkString
 
   def print_string_bytes(str: String): String =
     quote(UTF8.bytes(str).iterator.map(print_byte).mkString)
 
   def print_string_symbols(str: String): String =
     quote(Symbol.iterator(str).map(print_symbol).mkString)
 
 
   /* pair */
 
   def print_pair[A, B](f: A => String, g: B => String)(pair: (A, B)): String =
     "(" + f(pair._1) + ", " + g(pair._2) + ")"
 
 
   /* list */
 
   def print_list[A](f: A => String)(list: List[A]): String =
     "[" + commas(list.map(f)) + "]"
 
 
   /* properties */
 
   def print_properties(props: Properties.T): String =
     print_list(print_pair(print_string_bytes, print_string_bytes))(props)
 }