alloy support

samples/Alloy/file_system.als

@@ -0,0 +1,59 @@
+module examples/systems/file_system
+
+/*
+ * Model of a generic file system.
+ */
+
+abstract sig Object {}
+
+sig Name {}
+
+sig File extends Object {} { some d: Dir | this in d.entries.contents }
+
+sig Dir extends Object {
+  entries: set DirEntry,
+  parent: lone Dir
+} {
+  parent = this.~@contents.~@entries
+  all e1, e2 : entries | e1.name = e2.name => e1 = e2
+  this !in this.^@parent
+  this != Root => Root in this.^@parent
+}
+
+one sig Root extends Dir {} { no parent }
+
+lone sig Cur extends Dir {}
+
+sig DirEntry {
+  name: Name,
+  contents: Object
+} {
+  one this.~entries
+}
+
+
+/**
+ * all directories besides root have one parent
+ */
+pred OneParent_buggyVersion {
+    all d: Dir - Root | one d.parent
+}
+
+/**
+ * all directories besides root have one parent
+ */
+pred OneParent_correctVersion {
+    all d: Dir - Root | (one d.parent && one contents.d)
+}
+
+/**
+ * Only files may be linked (that is, have more than one entry)
+ * That is, all directories are the contents of at most one directory entry
+ */
+pred NoDirAliases {
+    all o: Dir | lone o.~contents
+}
+
+check { OneParent_buggyVersion => NoDirAliases } for 5 expect 1
+
+check { OneParent_correctVersion => NoDirAliases } for 5 expect 0