Isabelle system support.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Tools/isabelle_system.scala	Sat Aug 16 16:01:53 2008 +0200
@@ -0,0 +1,26 @@
+/*  Title:      Pure/Tools/isabelle_system.scala
+    ID:         $Id$
+    Author:     Makarius
+
+Isabelle system support.
+*/
+
+package isabelle
+
+
+object IsabelleSystem {
+
+  /* Isabelle settings */
+
+  class BadSetting(val name: String) extends Exception
+
+  private def strict_getenv(name: String) = {
+    val value = System.getenv(name)
+    if (value == null || value == "") throw new BadSetting(name)
+    else value
+  }
+
+  def ISABELLE_HOME() = strict_getenv("ISABELLE_HOME_JVM")
+  def ISABELLE_HOME_USER() = strict_getenv("ISABELLE_HOME_USER_JVM")
+
+}