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diff --git a/src/libnix/normalise.hh b/src/libnix/normalise.hh
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+++ b/src/libnix/normalise.hh
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+#ifndef __NORMALISE_H
+#define __NORMALISE_H
+
+#include "expr.hh"
+
+
+/* Normalise a Nix expression.  That is, if the expression is a
+   derivation, a path containing an equivalent closure expression is
+   returned.  This requires that the derivation is performed, unless a
+   successor is known. */
+Path normaliseNixExpr(const Path & nePath, PathSet pending = PathSet());
+
+/* Realise a closure expression in the file system. 
+
+   The pending paths are those that are already being realised.  This
+   prevents infinite recursion for paths realised through a substitute
+   (since when we build the substitute, we would first try to realise
+   its output paths through substitutes... kaboom!). */
+void realiseClosure(const Path & nePath, PathSet pending = PathSet());
+
+/* Ensure that a path exists, possibly by instantiating it by
+   realising a substitute. */
+void ensurePath(const Path & path, PathSet pending = PathSet());
+
+/* Read a Nix expression, after ensuring its existence through
+   ensurePath(). */
+NixExpr exprFromPath(const Path & path, PathSet pending = PathSet());
+
+/* Get the list of root (output) paths of the given Nix expression. */
+PathSet nixExprRoots(const Path & nePath);
+
+/* Get the list of paths that are required to realise the given
+   expression.  For a derive expression, this is the union of
+   requisites of the inputs; for a closure expression, it is the path of
+   each element in the closure.  If `includeExprs' is true, include the
+   paths of the Nix expressions themselves.  If `includeSuccessors' is
+   true, include the requisites of successors. */
+PathSet nixExprRequisites(const Path & nePath,
+    bool includeExprs, bool includeSuccessors);
+
+/* Return the list of the paths of all known Nix expressions whose
+   output paths are completely contained in the set `outputs'. */
+PathSet findGenerators(const PathSet & outputs);
+
+
+#endif /* !__NORMALISE_H */