From b9f09b3268bf0c3d9ecd512dd3a0aa1247550cc2 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 16 Jun 2003 07:03:40 +0000 Subject: [PATCH] * AST for Nix expressions. --- src/nix.cc | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 67 insertions(+), 3 deletions(-) diff --git a/src/nix.cc b/src/nix.cc index ea33e5e28..7990cde3a 100644 --- a/src/nix.cc +++ b/src/nix.cc @@ -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)