* Refactoring on the file names.

src/fstate.hh

@@ -0,0 +1,80 @@
+#ifndef __EVAL_H
+#define __EVAL_H
+
+extern "C" {
+#include <aterm2.h>
+}
+
+#include "hash.hh"
+
+using namespace std;
+
+
+/* \section{Abstract syntax of Nix file system state expressions}
+
+   A Nix file system state expression, or FState, describes a
+   (partial) state of the file system.
+
+     Path : Path * Content * [FState] -> FState
+
+   Path(path, content, refs) specifies a file object (its full path
+   and contents), along with all file objects referenced by it (that
+   is, that it has pointers to).  We assume that all files are
+   self-referential.  This prevents us from having to deal with
+   cycles.
+
+     Derive : String * Path * [FState] * Path * [(String, String)] -> FState
+
+   Derive(platform, builder, ins, outs, env) specifies the creation of
+   new file objects (in paths declared by `outs') by the execution of
+   a program `builder' on a platform `platform'.  This execution takes
+   place in a file system state given by `ins'.  `env' specifies a
+   mapping of strings to strings.
+
+     [ !!! NOT IMPLEMENTED 
+       Regular : String -> Content
+       Directory : [(String, Content)] -> Content
+       (this complicates unambiguous normalisation)
+     ]
+     CHash : Hash -> Content
+
+   File content, given either in situ, or through an external reference
+   to the file system or url-space decorated with a hash to preserve
+   purity.
+
+   A FState expression is in {\em $f$-normal form} if all Derive nodes
+   have been reduced to File nodes.
+
+   DISCUSSION: the idea is that a Regular/Directory is interchangeable
+   with its CHash.  This would appear to break referential
+   transparency, e.g., Derive(..., ..., [...CHash(h)...], ...) can
+   only be reduced in a context were the Regular/Directory equivalent
+   of Hash(h) is known.  However, CHash should be viewed strictly as a
+   shorthand; that is, when we export an expression containing a
+   CHash, we should also export the file object referenced by that
+   CHash.
+
+*/
+
+typedef ATerm FState;
+typedef ATerm Content;
+
+
+/* Realise a $f$-normalised expression in the file system. */
+FState realiseFState(FState fs);
+
+/* 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);
+
+/* Write an aterm to the Nix store directory, and return its hash. */
+Hash writeTerm(ATerm t);
+
+
+#endif /* !__EVAL_H */