* Basic work on allowing derive expressions to build multiple paths.

  This is not entirely trivial since this introduces the possibility
  of mutual recursion.
* Made normal forms self-contained.
* Use unique ids, not content hashes, for content referencing.

7 files changed, 366 insertions, 193 deletions

diff --git a/src/fstate.cc b/src/fstate.cc
index 36f7482acf9d..596d63a5f406 100644
--- a/src/fstate.cc
+++ b/src/fstate.cc
@@ -154,55 +154,47 @@ FState hash2fstate(Hash hash)
 }
 
 
-ATerm termFromHash(const Hash & hash, string * p)
+ATerm termFromId(const FSId & id, string * p)
 {
-    string path = expandHash(hash);
+    string path = expandId(id);
     if (p) *p = path;
     ATerm t = ATreadFromNamedFile(path.c_str());
-    if (!t) throw Error(format("cannot read aterm %1%") % path);
+    if (!t) throw Error(format("cannot read aterm from `%1%'") % path);
     return t;
 }
 
 
-Hash writeTerm(ATerm t, const string & suffix, string * p)
+FSId writeTerm(ATerm t, const string & suffix, string * p)
 {
-    string path = nixStore + "/tmp.nix"; /* !!! */
+    FSId id = hashTerm(t);
+
+    string path = canonPath(nixStore + "/" + 
+        (string) id + suffix + ".nix");
     if (!ATwriteToNamedTextFile(t, path.c_str()))
         throw Error(format("cannot write aterm %1%") % path);
-    Hash hash = hashPath(path);
-    string path2 = canonPath(nixStore + "/" + 
-        (string) hash + suffix + ".nix");
-    if (rename(path.c_str(), path2.c_str()) == -1)
-        throw SysError(format("renaming %1% to %2%") % path % path2);
-    registerPath(path2, hash);
-    if (p) *p = path2;
-    return hash;
+
+    registerPath(path, id);
+    if (p) *p = path;
+
+    return id;
 }
 
 
-void registerSuccessor(const Hash & fsHash, const Hash & scHash)
+void registerSuccessor(const FSId & id1, const FSId & id2)
 {
-    setDB(nixDB, dbSuccessors, fsHash, scHash);
+    setDB(nixDB, dbSuccessors, id1, id2);
 }
 
 
-FState storeSuccessor(FState fs, FState sc, StringSet & paths)
+static FSId storeSuccessor(const FSId & id1, FState sc)
 {
-    if (fs == sc) return sc;
-    
-    string path;
-    Hash fsHash = hashTerm(fs);
-    Hash scHash = writeTerm(sc, "-s-" + (string) fsHash, &path);
-    registerSuccessor(fsHash, scHash);
-    paths.insert(path);
-
-#if 0
-    return ATmake("Include(<str>)", ((string) scHash).c_str());
-#endif
-    return sc;
+    FSId id2 = writeTerm(sc, "-s-" + (string) id1, 0);
+    registerSuccessor(id1, id2);
+    return id2;
 }
 
 
+#if 0
 static FState realise(FState fs, StringSet & paths)
 {
     char * s1, * s2, * s3;
@@ -421,3 +413,193 @@ void fstateRefs(FState fs, StringSet & paths)
 {
     fstateRefs2(fs, paths);
 }
+#endif
+
+
+static void parseIds(ATermList ids, FSIds & out)
+{
+    while (!ATisEmpty(ids)) {
+        char * s;
+        ATerm id = ATgetFirst(ids);
+        if (!ATmatch(id, "<str>", &s))
+            throw badTerm("not an id", id);
+        out.push_back(parseHash(s));
+        debug(s);
+        ids = ATgetNext(ids);
+    }
+}
+
+
+/* Parse a slice. */
+static Slice parseSlice(FState fs)
+{
+    Slice slice;
+    ATermList roots, elems;
+    
+    if (!ATmatch(fs, "Slice([<list>], [<list>])", &roots, &elems))
+        throw badTerm("not a slice", fs);
+
+    parseIds(roots, slice.roots);
+
+    while (!ATisEmpty(elems)) {
+        char * s1, * s2;
+        ATermList refs;
+        ATerm t = ATgetFirst(elems);
+        if (!ATmatch(t, "(<str>, <str>, [<list>])", &s1, &s2, &refs))
+            throw badTerm("not a slice element", t);
+        SliceElem elem;
+        elem.path = s1;
+        elem.id = parseHash(s2);
+        parseIds(refs, elem.refs);
+        slice.elems.push_back(elem);
+        elems = ATgetNext(elems);
+    }
+
+    return slice;
+}
+
+
+Slice normaliseFState(FSId id)
+{
+    debug(format("normalising fstate"));
+    Nest nest(true);
+
+    /* Try to substitute $id$ by any known successors in order to
+       speed up the rewrite process. */
+    string idSucc;
+    while (queryDB(nixDB, dbSuccessors, id, idSucc)) {
+        debug(format("successor %1% -> %2%") % (string) id % idSucc);
+        id = parseHash(idSucc);
+    }
+
+    /* Get the fstate expression. */
+    FState fs = termFromId(id);
+
+    /* Already in normal form (i.e., a slice)? */
+    if (ATgetType(fs) == AT_APPL && 
+        (string) ATgetName(ATgetAFun(fs)) == "Slice")
+        return parseSlice(fs);
+    
+    /* Then we it's a Derive node. */
+    ATermList outs, ins, bnds;
+    char * builder;
+    char * platform;
+    if (!ATmatch(fs, "Derive([<list>], [<list>], <str>, <str>, [<list>])",
+            &outs, &ins, &builder, &platform, &bnds))
+        throw badTerm("not a derive", fs);
+
+    /* Right platform? */
+    checkPlatform(platform);
+        
+    /* Realise inputs (and remember all input paths). */
+    FSIds inIds;
+    parseIds(ins, inIds);
+    
+    SliceElems inElems; /* !!! duplicates */
+    StringSet inPathsSet;
+    for (FSIds::iterator i = inIds.begin(); i != inIds.end(); i++) {
+        Slice slice = normaliseFState(*i);
+        realiseSlice(slice);
+
+        for (SliceElems::iterator j = slice.elems.begin();
+             j != slice.elems.end(); j++)
+        {
+            inElems.push_back(*j);
+            inPathsSet.insert(j->path);
+        }
+    }
+
+    Strings inPaths;
+    copy(inPathsSet.begin(), inPathsSet.end(),
+        inserter(inPaths, inPaths.begin()));
+
+    /* Build the environment. */
+    Environment env;
+    while (!ATisEmpty(bnds)) {
+        char * s1, * s2;
+        ATerm bnd = ATgetFirst(bnds);
+        if (!ATmatch(bnd, "(<str>, <str>)", &s1, &s2))
+            throw badTerm("tuple of strings expected", bnd);
+        env[s1] = s2;
+        bnds = ATgetNext(bnds);
+    }
+
+    /* Check that none of the output paths exist. */
+    typedef pair<string, FSId> OutPath;
+    list<OutPath> outPaths;
+    while (!ATisEmpty(outs)) {
+        ATerm t = ATgetFirst(outs);
+        char * s1, * s2;
+        if (!ATmatch(t, "(<str>, <str>)", &s1, &s2))
+            throw badTerm("string expected", t);
+        outPaths.push_back(OutPath(s1, parseHash(s2)));
+        outs = ATgetNext(outs);
+    }
+
+    for (list<OutPath>::iterator i = outPaths.begin(); 
+         i != outPaths.end(); i++)
+        if (pathExists(i->first))
+            throw Error(format("path `%1%' exists") % i->first);
+
+    /* Run the builder. */
+    runProgram(builder, env);
+        
+    Slice slice;
+
+    /* Check whether the output paths were created, and register each
+       one. */
+    for (list<OutPath>::iterator i = outPaths.begin(); 
+         i != outPaths.end(); i++)
+    {
+        string path = i->first;
+        if (!pathExists(path))
+            throw Error(format("path `%1%' does not exist") % path);
+        registerPath(path, i->second);
+        slice.roots.push_back(i->second);
+
+        Strings outPaths = filterReferences(path, inPaths);
+    }
+
+    return slice;
+}
+
+
+void realiseSlice(Slice slice)
+{
+    debug(format("realising slice"));
+    Nest nest(true);
+
+    if (slice.elems.size() == 0)
+        throw Error("empty slice");
+
+    /* Perhaps all paths already contain the right id? */
+
+    bool missing = false;
+    for (SliceElems::iterator i = slice.elems.begin();
+         i != slice.elems.end(); i++)
+    {
+        SliceElem elem = *i;
+        string id;
+        if (!queryDB(nixDB, dbPath2Id, elem.path, id)) {
+            if (pathExists(elem.path))
+                throw Error(format("path `%1%' obstructed") % elem.path);
+            missing = true;
+            break;
+        }
+        if (parseHash(id) != elem.id)
+            throw Error(format("path `%1%' obstructed") % elem.path);
+    }
+
+    if (!missing) {
+        debug(format("already installed"));
+        return;
+    }
+
+    /* For each element, expand its id at its path. */
+    for (SliceElems::iterator i = slice.elems.begin();
+         i != slice.elems.end(); i++)
+    {
+        SliceElem elem = *i;
+        expandId(elem.id, elem.path);
+    }
+}
diff --git a/src/fstate.hh b/src/fstate.hh
index 9d789c834685..f06a4807ef5d 100644
--- a/src/fstate.hh
+++ b/src/fstate.hh
@@ -8,6 +8,7 @@ extern "C" {
 }
 
 #include "hash.hh"
+#include "store.hh"
 
 using namespace std;
 
@@ -17,33 +18,24 @@ using namespace std;
    A Nix file system state expression, or FState, describes a
    (partial) state of the file system.
 
-     Path : Path * Content * [FState] -> FState
+     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 : String * Path * [FState] * Path * [(String, String)] -> FState
+     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.
 
-     [ !!! 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.
 
@@ -63,7 +55,26 @@ 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);
@@ -74,6 +85,8 @@ 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);
@@ -85,16 +98,22 @@ Error badTerm(const format & f, ATerm t);
 /* Hash an aterm. */
 Hash hashTerm(ATerm t);
 
-FState hash2fstate(Hash hash);
-
-/* Read an aterm from disk, given its hash. */
-ATerm termFromHash(const Hash & hash, string * p = 0);
+/* 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. */
-Hash writeTerm(ATerm t, const string & suffix, string * p = 0);
+FSId writeTerm(ATerm t, const string & suffix, string * p = 0);
 
 /* Register a successor. */
-void registerSuccessor(const Hash & fsHash, const Hash & scHash);
+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 */
diff --git a/src/globals.cc b/src/globals.cc
index 9893d7ad22b4..1edb38f7483e 100644
--- a/src/globals.cc
+++ b/src/globals.cc
@@ -2,7 +2,8 @@
 #include "db.hh"
 
 
-string dbHash2Paths = "hash2paths";
+string dbPath2Id = "path2id";
+string dbId2Paths = "id2paths";
 string dbSuccessors = "successors";
 string dbSubstitutes = "substitutes";
 
@@ -15,7 +16,8 @@ string nixDB = "/UNINIT";
 
 void initDB()
 {
-    createDB(nixDB, dbHash2Paths);
+    createDB(nixDB, dbPath2Id);
+    createDB(nixDB, dbId2Paths);
     createDB(nixDB, dbSuccessors);
     createDB(nixDB, dbSubstitutes);
 }
diff --git a/src/globals.hh b/src/globals.hh
index 0668ac40e57e..fbb020df7c91 100644
--- a/src/globals.hh
+++ b/src/globals.hh
@@ -8,33 +8,36 @@ using namespace std;
 
 /* Database names. */
 
-/* dbHash2Paths :: Hash -> [Path]
+/* dbPath2Id :: Path -> FSId
 
-   Maintains a mapping from hashes to lists of paths.  This is what we
-   use to resolve Hash(hash) content descriptors. */
-extern string dbHash2Paths;
+   Each pair (p, id) records that path $p$ contains an expansion of
+   $id$. */
+extern string dbPath2Id;
 
-/* dbSuccessors :: Hash -> Hash
 
-   Each pair (h1, h2) in this mapping records the fact that a
-   successor of an fstate expression with hash h1 is stored in a file
-   with hash h2.
+/* dbId2Paths :: FSId -> [Path]
+
+   A mapping from ids to lists of paths. */
+extern string dbId2Paths;
+
+
+/* dbSuccessors :: FSId -> FSId
+
+   Each pair $(id_1, id_2)$ in this mapping records the fact that a
+   successor of an fstate expression stored in a file with identifier
+   $id_1$ is stored in a file with identifier $id_2$.
 
    Note that a term $y$ is successor of $x$ iff there exists a
    sequence of rewrite steps that rewrites $x$ into $y$.
-
-   Also note that instead of a successor, $y$ can be any term
-   equivalent to $x$, that is, reducing to the same result, as long as
-   $x$ is equal to or a successor of $y$.  (This is useful, e.g., for
-   shared derivate caching over the network).
 */
 extern string dbSuccessors;
 
-/* dbSubstitutes :: Hash -> [Hash]
 
-   Each pair $(h, [hs])$ tells Nix that it can realise any of the
-   fstate expressions referenced by the hashes in $hs$ to obtain a Nix
-   archive that, when unpacked, will produce a path with hash $h$.
+/* dbSubstitutes :: FSId -> [FSId]
+
+   Each pair $(id, [ids])$ tells Nix that it can realise any of the
+   fstate expressions referenced by the identifiers in $ids$ to
+   generate a path with identifier $id$.
 
    The main purpose of this is for distributed caching of derivates.
    One system can compute a derivate with hash $h$ and put it on a
diff --git a/src/store.cc b/src/store.cc
index 5feb80c9de78..c8b3bd37f4e5 100644
--- a/src/store.cc
+++ b/src/store.cc
@@ -84,39 +84,36 @@ void copyPath(string src, string dst)
 }
 
 
-void registerSubstitute(const Hash & srcHash, const Hash & subHash)
+void registerSubstitute(const FSId & srcId, const FSId & subId)
 {
     Strings subs;
-    queryListDB(nixDB, dbSubstitutes, srcHash, subs); /* non-existence = ok */
+    queryListDB(nixDB, dbSubstitutes, srcId, subs); /* non-existence = ok */
 
     for (Strings::iterator it = subs.begin(); it != subs.end(); it++)
-        if (parseHash(*it) == subHash) return;
+        if (parseHash(*it) == subId) return;
     
-    subs.push_back(subHash);
+    subs.push_back(subId);
     
-    setListDB(nixDB, dbSubstitutes, srcHash, subs);
+    setListDB(nixDB, dbSubstitutes, srcId, subs);
 }
 
 
-Hash registerPath(const string & _path, Hash hash)
+void registerPath(const string & _path, const FSId & id)
 {
     string path(canonPath(_path));
 
-    if (hash == Hash()) hash = hashPath(path);
+    setDB(nixDB, dbPath2Id, path, id);
 
     Strings paths;
-    queryListDB(nixDB, dbHash2Paths, hash, paths); /* non-existence = ok */
+    queryListDB(nixDB, dbId2Paths, id, paths); /* non-existence = ok */
 
     for (Strings::iterator it = paths.begin();
          it != paths.end(); it++)
-        if (*it == path) goto exists;
+        if (*it == path) return;
     
     paths.push_back(path);
     
-    setListDB(nixDB, dbHash2Paths, hash, paths);
-    
- exists:
-    return hash;
+    setListDB(nixDB, dbId2Paths, id, paths);
 }
 
 
@@ -124,10 +121,15 @@ void unregisterPath(const string & _path)
 {
     string path(canonPath(_path));
 
-    Hash hash = hashPath(path);
+    string _id;
+    if (!queryDB(nixDB, dbPath2Id, path, _id))
+        return;
+    FSId id(parseHash(_id));
+
+    /* begin transaction */
     
     Strings paths, paths2;
-    queryListDB(nixDB, dbHash2Paths, hash, paths); /* non-existence = ok */
+    queryListDB(nixDB, dbId2Paths, id, paths); /* non-existence = ok */
 
     bool changed = false;
     for (Strings::iterator it = paths.begin();
@@ -135,7 +137,9 @@ void unregisterPath(const string & _path)
         if (*it != path) paths2.push_back(*it); else changed = true;
 
     if (changed)
-        setListDB(nixDB, dbHash2Paths, hash, paths2);
+        setListDB(nixDB, dbId2Paths, id, paths2);
+
+    /* end transaction */
 }
 
 
@@ -146,7 +150,7 @@ bool isInPrefix(const string & path, const string & _prefix)
 }
 
 
-string expandHash(const Hash & hash, const string & target,
+string expandId(const FSId & id, const string & target,
     const string & prefix)
 {
     Strings paths;
@@ -154,9 +158,7 @@ string expandHash(const Hash & hash, const string & target,
     if (!target.empty() && !isInPrefix(target, prefix))
         abort();
 
-    queryListDB(nixDB, dbHash2Paths, hash, paths);
-
-    /* !!! we shouldn't check for staleness by default --- too slow */
+    queryListDB(nixDB, dbId2Paths, id, paths);
 
     /* Pick one equal to `target'. */
     if (!target.empty()) {
@@ -165,16 +167,8 @@ string expandHash(const Hash & hash, const string & target,
              i != paths.end(); i++)
         {
             string path = *i;
-            try {
-#if 0
-                if (path == target && hashPath(path) == hash)
-#endif
-                if (path == target && pathExists(path))
-                    return path;
-            } catch (Error & e) {
-                debug(format("stale path: %1%") % e.msg());
-                /* try next one */
-            }
+            if (path == target && pathExists(path))
+                return path;
         }
         
     }
@@ -184,28 +178,26 @@ string expandHash(const Hash & hash, const string & target,
          it != paths.end(); it++)
     {
         string path = *it;
-        try {
-            if (isInPrefix(path, prefix) && hashPath(path) == hash) {
-                if (target.empty())
-                    return path;
-                else {
-                    copyPath(path, target);
-                    return target;
-                }
+        if (isInPrefix(path, prefix) && pathExists(path)) {
+            if (target.empty())
+                return path;
+            else {
+                copyPath(path, target);
+                registerPath(target, id);
+                return target;
             }
-        } catch (Error & e) {
-            debug(format("stale path: %1%") % e.msg());
-            /* try next one */
         }
     }
 
+#if 0
     /* Try to realise the substitutes. */
 
     Strings subs;
-    queryListDB(nixDB, dbSubstitutes, hash, subs); /* non-existence = ok */
+    queryListDB(nixDB, dbSubstitutes, id, subs); /* non-existence = ok */
 
     for (Strings::iterator it = subs.begin(); it != subs.end(); it++) {
-        StringSet dummy;
+        realiseSlice(normaliseFState(*it));
+        
         FState nf = realiseFState(hash2fstate(parseHash(*it)), dummy);
         string path = fstatePath(nf);
 
@@ -222,29 +214,30 @@ string expandHash(const Hash & hash, const string & target,
             return target;
         }
     }
+#endif
     
-    throw Error(format("cannot expand hash `%1%'") % (string) hash);
+    throw Error(format("cannot expand id `%1%'") % (string) id);
 }
 
     
-void addToStore(string srcPath, string & dstPath, Hash & hash,
+void addToStore(string srcPath, string & dstPath, FSId & id,
     bool deterministicName)
 {
     srcPath = absPath(srcPath);
-    hash = hashPath(srcPath);
+    id = hashPath(srcPath);
 
     string baseName = baseNameOf(srcPath);
-    dstPath = canonPath(nixStore + "/" + (string) hash + "-" + baseName);
+    dstPath = canonPath(nixStore + "/" + (string) id + "-" + baseName);
 
     try {
         /* !!! should not use the substitutes! */
-        dstPath = expandHash(hash, deterministicName ? dstPath : "", nixStore);
+        dstPath = expandId(id, deterministicName ? dstPath : "", nixStore);
         return;
     } catch (...) {
     }
     
     copyPath(srcPath, dstPath);
-    registerPath(dstPath, hash);
+    registerPath(dstPath, id);
 }
 
 
diff --git a/src/store.hh b/src/store.hh
index b6ed43ff675b..7dd0f72e6f7c 100644
--- a/src/store.hh
+++ b/src/store.hh
@@ -8,29 +8,28 @@
 using namespace std;
 
 
+typedef Hash FSId;
+
+
 /* Copy a path recursively. */
 void copyPath(string src, string dst);
 
 /* Register a substitute. */
-void registerSubstitute(const Hash & srcHash, const Hash & subHash);
+void registerSubstitute(const FSId & srcId, const FSId & subId);
 
-/* Register a path keyed on its hash. */
-Hash registerPath(const string & path, Hash hash = Hash());
+/* Register a path keyed on its id. */
+void registerPath(const string & path, const FSId & id);
 
 /* Return a path whose contents have the given hash.  If target is
    not empty, ensure that such a path is realised in target (if
    necessary by copying from another location).  If prefix is not
-   empty, only return a path that is an descendent of prefix. 
-
-   If no path with the given hash is known to exist in the file
-   system, 
-*/
-string expandHash(const Hash & hash, const string & target = "",
+   empty, only return a path that is an descendent of prefix. */
+string expandId(const FSId & id, const string & target = "",
     const string & prefix = "/");
 
 /* Copy a file to the nixStore directory and register it in dbRefs.
    Return the hash code of the value. */
-void addToStore(string srcPath, string & dstPath, Hash & hash,
+void addToStore(string srcPath, string & dstPath, FSId & id,
     bool deterministicName = false);
 
 /* Delete a value from the nixStore directory. */
diff --git a/src/test.cc b/src/test.cc
index c2a1cd3bfd55..3437650ac217 100644
--- a/src/test.cc
+++ b/src/test.cc
@@ -11,14 +11,15 @@
 #include "globals.hh"
 
 
-void realise(FState fs)
+void realise(FSId id)
 {
-    cout << format("%1% => %2%\n")
-        % printTerm(fs)
-        % printTerm(realiseFState(fs));
+    cout << format("realising %1%\n") % (string) id;
+    Slice slice = normaliseFState(id);
+    realiseSlice(slice);
 }
 
 
+#if 0
 void realiseFail(FState fs)
 {
     try {
@@ -28,6 +29,7 @@ void realiseFail(FState fs)
         cout << "error (expected): " << e.what() << endl;
     }
 }
+#endif
 
 
 struct MySink : DumpSink
@@ -111,54 +113,47 @@ void runTests()
 
     /* Expression evaluation. */
 
-#if 0
-    eval(whNormalise,
-        ATmake("Str(\"Hello World\")"));
-    eval(whNormalise,
-        ATmake("Bool(True)"));
-    eval(whNormalise,
-        ATmake("Bool(False)"));
-    eval(whNormalise,
-        ATmake("App(Lam(\"x\", Var(\"x\")), Str(\"Hello World\"))"));
-    eval(whNormalise,
-        ATmake("App(App(Lam(\"x\", Lam(\"y\", Var(\"x\"))), Str(\"Hello World\")), Str(\"Hallo Wereld\"))"));
-    eval(whNormalise,
-        ATmake("App(Lam(\"sys\", Lam(\"x\", [Var(\"x\"), Var(\"sys\")])), Str(\"i686-suse-linux\"))"));
-
-    evalFail(whNormalise,
-        ATmake("Foo(123)"));
-
-    string builder1fn = absPath("./test-builder-1.sh");
-    Hash builder1h = hashPath(builder1fn);
-
-    string fn1 = nixValues + "/builder-1.sh";
-    Expr e1 = ATmake("Path(<str>, ExtFile(<str>, <str>), [])", 
-        fn1.c_str(),
-        builder1h.c_str(),
-        builder1fn.c_str());
-    eval(fNormalise, e1);
-
-    string fn2 = nixValues + "/refer.txt";
-    Expr e2 = ATmake("Path(<str>, Regular(<str>), [<term>])",
-        fn2.c_str(),
-        ("I refer to " + fn1).c_str(),
-        e1);
-    eval(fNormalise, e2);
-
-    realise(e2);
-#endif
-
-    Hash builder1h;
+    FSId builder1id;
     string builder1fn;
-    addToStore("./test-builder-1.sh", builder1fn, builder1h);
+    addToStore("./test-builder-1.sh", builder1fn, builder1id);
 
     FState fs1 = ATmake(
-        "Path(<str>, Hash(<str>), [])", 
+        "Slice([<str>], [(<str>, <str>, [])])",
+        ((string) builder1id).c_str(),
         builder1fn.c_str(),
-        ((string) builder1h).c_str());
-    realise(fs1);
-    realise(fs1);
+        ((string) builder1id).c_str());
+    FSId fs1id = writeTerm(fs1, "", 0);
+
+    realise(fs1id);
+    realise(fs1id);
+
+    FState fs2 = ATmake(
+        "Slice([<str>], [(<str>, <str>, [])])",
+        ((string) builder1id).c_str(),
+        (builder1fn + "_bla").c_str(),
+        ((string) builder1id).c_str());
+    FSId fs2id = writeTerm(fs2, "", 0);
+
+    realise(fs2id);
+    realise(fs2id);
+
+    string out1fn = nixStore + "/hello.txt";
+    string out1id = hashString("foo"); /* !!! bad */
+    FState fs3 = ATmake(
+        "Derive([(<str>, <str>)], [<str>], <str>, <str>, [(\"out\", <str>)])",
+        out1fn.c_str(),
+        ((string) out1id).c_str(),
+        ((string) fs1id).c_str(),
+        ((string) builder1fn).c_str(),
+        thisSystem.c_str(),
+        out1fn.c_str());
+    debug(printTerm(fs3));
+    FSId fs3id = writeTerm(fs3, "", 0);
+
+    realise(fs3id);
+    realise(fs3id);
 
+#if 0
     FState fs2 = ATmake(
         "Path(<str>, Hash(<str>), [])", 
         (builder1fn + "_bla").c_str(),
@@ -175,28 +170,8 @@ void runTests()
         out1fn.c_str(),
         out1fn.c_str());
     realise(fs3);
-
-#if 0
-    Expr e1 = ATmake("Exec(Str(<str>), Hash(<str>), [])",
-        thisSystem.c_str(), ((string) builder1).c_str());
-
-    eval(e1);
-
-    Hash builder2 = addValue("./test-builder-2.sh");
-
-    Expr e2 = ATmake(
-        "Exec(Str(<str>), Hash(<str>), [Tup(Str(\"src\"), <term>)])",
-        thisSystem.c_str(), ((string) builder2).c_str(), e1);
-
-    eval(e2);
-
-    Hash h3 = addValue("./test-expr-1.nix");
-    Expr e3 = ATmake("Deref(Hash(<str>))", ((string) h3).c_str());
-
-    eval(e3);
-
-    deleteValue(h3);
 #endif
+
 }