YARN-913 Initial yarn registry just to get the git process booted

.gitignore

@@ -13,4 +13,8 @@ hs_err_pid*
 
 # Tex artifacts
 *.dvi
-*.aux
+*.aux
+*.pdf
+*.log
+.project
+*.toolbox

tlaspecs/yarnregistry/yarnregistry.tla

@@ -0,0 +1,57 @@
+---------------------------- MODULE yarnregistry ----------------------------
+
+
+EXTENDS Sequences
+
+(* a path element is all chars excluding "/" *)
+
+CONSTANTS
+            PathChars,  \* the set of valid characters in a path 
+            Paths,      \* the set of all possible valid paths 
+            Data        \* the set of all possible sequences of bytes
+
+
+
+(* all paths in the system *)
+VARIABLE registryPaths
+
+PathCharInvariant == PathChars \subseteq STRING 
+
+PathInvariant == \A p \in registryPaths:  \A pe \in p : pe \in PathChars
+
+(*
+isRoot[P] == p = []
+*) 
+(* parent(p, q) == *) 
+
+=============================================================================
+
+(*
+An Entry is defined as a path, an ephemerality flag, and  the actual data which it contains.
+
+By including the path in an entry, we avoid having to define some function
+mapping Path -> entry. Instead a registry can be defined as a set of RegistryEntries
+matching the validity critera.
+
+*)
+
+RegistryEntry == [
+        path: Paths,                \* The path to the entry
+        ephemeral: BOOLEAN,         \* A flag to indicate when the entry is ephemeral
+        data: Data]                 \* the data in the entry
+
+
+(***************************************************************************
+For validity, all entries must match the following criteria
+
+* there can be at most one entry with a given path in the set
+* their path is either [] or a parent path which must also be found in the registry
+* no entry may have a parent that is ephemeral
+
+ ***************************************************************************)
+
+=============================================================================
+=============================================================================
+\* Modification History
+\* Last modified Mon Sep 01 18:50:01 BST 2014 by stevel
+\* Created Sun Aug 31 14:54:47 BST 2014 by stevel