case branches support constant sets for convenience

doc/manual.txt

@@ -1527,6 +1527,27 @@ given, control passes after the ``case`` statement.
 To suppress the static error in the ordinal case an ``else`` part with a ``nil``
 statement can be used.
 
+As a special semantic extension, an expression in an ``of`` branch of a case
+statement may evaluate to a set constructor; the set is then expanded into 
+a list of its elements:
+
+.. code-block:: nimrod
+  const
+    SymChars: set[char] = {'a'..'z', 'A'..'Z', '\x80'..'\xFF'}
+
+  proc classify(s: string) =
+    case s[0]
+    of SymChars, '_': echo "an identifier"
+    of '0'..'9': echo "a number"
+    else: echo "other"
+  
+  # is equivalent to:
+  proc classify(s: string) =
+    case s[0]
+    of 'a'..'z', 'A'..'Z', '\x80'..'\xFF', '_': echo "an identifier"
+    of '0'..'9': echo "a number"
+    else: echo "other"
+
 
 When statement
 ~~~~~~~~~~~~~~