* Synchronise terminology with the ICSE paper (e.g., slice -> closure,

fstate -> Nix expression).
* Fix src/test.cc.

src/expr.hh

@@ -0,0 +1,73 @@
+#ifndef __FSTATE_H
+#define __FSTATE_H
+
+extern "C" {
+#include <aterm2.h>
+}
+
+#include "store.hh"
+
+
+/* Abstract syntax of Nix expressions. */
+
+typedef list<FSId> FSIds;
+
+struct ClosureElem
+{
+    FSId id;
+    StringSet refs;
+};
+
+typedef map<string, ClosureElem> ClosureElems;
+
+struct Closure
+{
+    StringSet roots;
+    ClosureElems elems;
+};
+
+typedef map<string, FSId> DerivationOutputs;
+typedef map<string, string> StringPairs;
+
+struct Derivation
+{
+    DerivationOutputs outputs;
+    FSIdSet inputs;
+    string platform;
+    string builder;
+    Strings args;
+    StringPairs env;
+};
+
+struct NixExpr
+{
+    enum { neClosure, neDerivation } type;
+    Closure closure;
+    Derivation derivation;
+};
+
+
+/* Return a canonical textual representation of an expression. */
+string printTerm(ATerm t);
+
+/* Throw an exception with an error message containing the given
+   aterm. */
+Error badTerm(const format & f, ATerm t);
+
+/* Hash an aterm. */
+Hash hashTerm(ATerm t);
+
+/* Read an aterm from disk, given its id. */
+ATerm termFromId(const FSId & id);
+
+/* Write an aterm to the Nix store directory, and return its hash. */
+FSId writeTerm(ATerm t, const string & suffix, FSId id = FSId());
+
+/* Parse a Nix expression. */
+NixExpr parseNixExpr(ATerm t);
+
+/* Parse a Nix expression. */
+ATerm unparseNixExpr(const NixExpr & ne);
+
+
+#endif /* !__FSTATE_H */