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#ifndef __FSTATE_H
#define __FSTATE_H
#include <set>
extern "C" {
#include <aterm2.h>
}
#include "hash.hh"
#include "store.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.
Slice : [Id] * [(Path, Id, [Id])] -> FState
(update)
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 : [(Path, Id)] * [FStateId] * Path * [(String, String)] -> FState
(update)
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.
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;
typedef set<string> StringSet;
typedef list<FSId> FSIds;
struct SliceElem
{
string path;
FSId id;
FSIds refs;
};
typedef list<SliceElem> SliceElems;
struct Slice
{
FSIds roots;
SliceElems elems;
};
#if 0
/* Realise an fstate expression in the file system. This requires
execution of all Derive() nodes. */
FState realiseFState(FState fs, StringSet & paths);
/* Return the path of an fstate expression. An empty string is
returned if the term is not a valid fstate expression. (!!!) */
string fstatePath(FState fs);
/* Return the paths referenced by fstate expression. */
void fstateRefs(FState fs, StringSet & paths);
#endif
/* 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, string * p = 0);
/* Write an aterm to the Nix store directory, and return its hash. */
FSId writeTerm(ATerm t, const string & suffix, string * p = 0);
/* Register a successor. */
void registerSuccessor(const FSId & id1, const FSId & id2);
/* Normalise an fstate-expression, that is, return an equivalent
Slice. */
Slice normaliseFState(FSId id);
/* Realise a Slice in the file system. */
void realiseSlice(Slice slice);
#endif /* !__FSTATE_H */
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