* AST for Nix expressions.

This commit is contained in:
Eelco Dolstra 2003-06-16 07:03:40 +00:00
parent 21fe717ce2
commit b9f09b3268

View file

@ -23,17 +23,81 @@ using namespace std;
/* Database names. */
/* dbRefs :: Hash -> FileName
Maintains a mapping from hashes to filenames within the NixValues
directory. This mapping is for performance only; it can be
reconstructed unambiguously from the nixValues directory. The
reason is that names in this directory are not printed hashes but
also might carry some descriptive element (e.g.,
"aterm-2.0-ae749a..."). Without this mapping, looking up a value
would take O(n) time because we would need to read the entire
directory. */
static string dbRefs = "refs";
static string dbInstPkgs = "pkginst";
static string dbPrebuilts = "prebuilts";
/* dbNFs :: Hash -> Hash
Each pair (h1, h2) in this mapping records the fact that h2 is a
normal form obtained by evaluating the value h1.
We would really like to have h2 be the hash of the object
referenced by h2. However, that gives a cyclic dependency: to
compute the hash (and thus the file name) of the object, we need to
compute the object, but to do that, we need the file name of the
object.
So for now we abandon the requirement that
hashFile(dbRefs[h]) == h.
I.e., this property does not hold for computed normal forms.
Rather, we use h2 = hash(h1). This allows dbNFs to be
reconstructed. Perhaps using a pseudo random number would be
better to prevent the system from being subverted in some way.
*/
static string dbNFs = "nfs";
/* dbNetSources :: Hash -> URL
Each pair (hash, url) in this mapping states that the object
identified by hash can be obtained by fetching the object pointed
to by url.
TODO: this should be Hash -> [URL]
TODO: factor this out into a separate tool? */
static string dbNetSources = "netsources";
static string nixSourcesDir;
/* Path names. */
/* nixValues is the directory where all Nix values (both files and
directories, and both normal and non-normal forms) live. */
static string nixValues;
/* nixLogDir is the directory where we log evaluations. */
static string nixLogDir;
/* nixDB is the file name of the Berkeley DB database where we
maintain the dbXXX mappings. */
static string nixDB;
/* Abstract syntax of Nix values:
e := Hash(h) -- external reference
| Str(s) -- string constant
| Bool(b) -- boolean constant
| Name(e) -- "&" operator; pointer (file name) formation
| App(e, e) -- application
| Lam(x, e) -- lambda abstraction
| Exec(platform, e, e*)
-- primitive; execute e with args e* on platform
;
*/
/* Download object referenced by the given URL into the sources
directory. Return the file name it was downloaded to. */
string fetchURL(string url)