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* Normalisation.

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This commit is contained in:
Eelco Dolstra 2003-06-27 09:55:31 +00:00
parent 3ec5252582
commit d4c3edfaba
3 changed files with 233 additions and 46 deletions
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142
src/eval.cc
View file

@ -5,6 +5,7 @@
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fcntl.h>
#include "eval.hh"
#include "globals.hh"
@ -91,7 +92,7 @@ static Hash computeDerived(Hash sourceHash, string targetName,
}
#endif
build:
// build:
/* Fill in the environment. We don't bother freeing
the strings, since we'll exec or die soon
@ -210,13 +211,14 @@ Hash hashExpr(Expr e)
/* Evaluate an expression; the result must be a string. */
static string evalString(Expr e)
{
e = evalValue(e);
e = whNormalise(e);
char * s;
if (ATmatch(e, "Str(<str>)", &s)) return s;
else throw badTerm("string value expected", e);
}
#if 0
/* Evaluate an expression; the result must be a value reference. */
static Hash evalHash(Expr e)
{
@ -225,8 +227,10 @@ static Hash evalHash(Expr e)
if (ATmatch(e, "Hash(<str>)", &s)) return parseHash(s);
else throw badTerm("value reference expected", e);
}
#endif
#if 0
/* Evaluate a list of arguments into normal form. */
void evalArgs(ATermList args, ATermList & argsNF, Environment & env)
{
@ -255,6 +259,7 @@ void evalArgs(ATermList args, ATermList & argsNF, Environment & env)
argsNF = ATreverse(argsNF);
}
#endif
Expr substExpr(string x, Expr rep, Expr e)
@ -302,19 +307,13 @@ Expr substExpr(string x, Expr rep, Expr e)
}
#if 0
Expr evalValue(Expr e)
{
char * s;
Expr eBuildPlatform, eProg, e2, e3, e4;
ATermList args;
/* Normal forms. */
if (ATmatch(e, "Str(<str>)", &s) ||
ATmatch(e, "Bool(True)") ||
ATmatch(e, "Bool(False)") ||
ATmatch(e, "Lam(<str>, <term>)", &s, &e2))
return e;
/* Value references. */
if (ATmatch(e, "Hash(<str>)", &s)) {
parseHash(s); /* i.e., throw exception if not valid */
@ -329,14 +328,6 @@ Expr evalValue(Expr e)
return evalValue(e3);
}
/* Application. */
if (ATmatch(e, "App(<term>, <term>)", &e2, &e3)) {
e2 = evalValue(e2);
if (!ATmatch(e2, "Lam(<str>, <term>)", &s, &e4))
throw badTerm("expecting lambda", e2);
return evalValue(substExpr(s, e3, e4));
}
/* Execution primitive. */
if (ATmatch(e, "Exec(<term>, <term>, [<list>])",
@ -376,3 +367,120 @@ Expr evalValue(Expr e)
/* Barf. */
throw badTerm("invalid expression", e);
}
#endif
Expr whNormalise(Expr e)
{
char * s;
Expr e2, e3, e4, e5;
/* Normal forms. */
if (ATmatch(e, "Str(<str>)", &s) ||
ATmatch(e, "Bool(True)") ||
ATmatch(e, "Bool(False)") ||
ATmatch(e, "Lam(<str>, <term>)", &s, &e2) ||
ATmatch(e, "File(<str>, <term>, <term>)", &s, &e2, &e3) ||
ATmatch(e, "Derive(<term>, <term>, <term>, <term>)", &e2, &e3, &e4, &e5))
return e;
/* Application. */
if (ATmatch(e, "App(<term>, <term>)", &e2, &e3)) {
e2 = whNormalise(e2);
if (!ATmatch(e2, "Lam(<str>, <term>)", &s, &e4))
throw badTerm("expecting lambda", e2);
return whNormalise(substExpr(s, e3, e4));
}
throw badTerm("invalid expression", e);
}
Expr dNormalise(Expr e)
{
e = whNormalise(e);
/* !!! todo */
return e;
}
Expr fNormalise(Expr e)
{
e = dNormalise(e);
char * s;
Expr e2, e3;
if (ATmatch(e, "File(<str>, <term>, [<list>])", &s, &e2, &e3)) {
ATermList refs = (ATermList) e3, refs2 = ATempty;
while (!ATisEmpty(refs)) {
ATerm ref = ATgetFirst(refs);
refs2 = ATinsert(refs2, fNormalise(ref));
refs = ATgetNext(refs);
}
refs2 = ATreverse(refs2);
return ATmake("File(<str>, <term>, <term>)", s, e2, refs2);
}
else return e;
}
void writeContent(string path, Content content)
{
char * s;
if (ATmatch(content, "Regular(<str>)", &s)) {
int fd; /* !!! close on exception */
fd = open(path.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0666);
if (fd == -1)
throw SysError("creating file " + path);
int len = strlen(s);
if (write(fd, s, len) != len)
throw SysError("writing file " + path);
close(fd);
}
else throw badTerm("ill-formed content", content);
}
struct RStatus
{
/* !!! the comparator of this hash should match the semantics of
the file system */
map<string, Hash> paths;
};
static void realise2(RStatus & status, Expr e)
{
char * s;
Content content;
ATermList refs;
if (!ATmatch(e, "File(<str>, <term>, [<list>])", &s, &content, &refs))
throw badTerm("not f-normalised", e);
string path(s);
while (!ATisEmpty(refs)) {
realise2(status, ATgetFirst(refs));
refs = ATgetNext(refs);
}
writeContent(path, content);
}
void realise(Expr e)
{
RStatus status;
realise2(status, e);
}

71
src/eval.hh
View file

@ -10,14 +10,14 @@ extern "C" {
using namespace std;
/* Abstract syntax of Nix expressions.
/* \section{Abstract syntax of Nix expressions}
An expression describes a (partial) state of the file system in a
referentially transparent way. The operational effect of
evaluating an expression is that the state described by the
expression is realised.
File : String * Content * [Expr] -> Expr
File : Path * Content * [Expr] -> Expr
File(path, content, refs) specifies a file object (its full path
and contents), along with all file objects referenced by it (that
@ -25,12 +25,13 @@ using namespace std;
self-referential. This prevents us from having to deal with
cycles.
Derive : String * Expr * [Expr] * [String] -> Expr
Derive : String * Path * [Expr] * [Expr] * [Expr] -> Expr
Derive(platform, builder, ins, outs) 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 and in an environment given by `ins'.
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.
Str : String -> Expr
@ -40,39 +41,73 @@ using namespace std;
Tuples of expressions.
Regular : String -> Content
Directory : [(String, Content)] -> Content
Hash : String -> Content
[ !!! NOT IMPLEMENTED
Regular : String -> Content
Directory : [(String, Content)] -> Content
(this complicates unambiguous normalisation)
]
CHash : Hash -> Content
File content, given either explicitly or implicitly through a cryptographic hash.
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.
The set of expressions in {\em $f$-normal form} is as follows:
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.
File : String * Content * [FExpr] -> FExpr
These are completely evaluated Nix expressions.
\section{Reduction rules}
The set of expressions in {\em $d$-normal form} is as follows:
...
\section{Normals forms}
An expression is in {\em weak head normal form} if it is a lambda,
a string or boolean value, or a File or Derive value.
An expression is in {\em $d$-normal form} if it matches the
signature FExpr:
File : String * Content * [DExpr] -> DExpr
Derive : String * DExpr * [Tup] * [String] -> DExpr
Derive : String * Path * [Tup] * [Tup2] -> DExpr
Tup : Str * DExpr -> Tup
Tup : Str * Str -> Tup
Tup : Str * Str -> Tup2
Str : String -> Str
These are Nix expressions in which the file system result of Derive
expressions has not yet been computed. This is useful for, e.g.,
querying dependencies.
An expression is in {\em $f$-normal form} if it matches the
signature FExpr:
File : String * Content * [FExpr] -> FExpr
These are completely evaluated Nix expressions.
*/
typedef ATerm Expr;
typedef ATerm Content;
/* Evaluate an expression. */
Expr evalValue(Expr e);
/* Expression normalisation. */
Expr whNormalise(Expr e);
Expr dNormalise(Expr e);
Expr fNormalise(Expr e);
/* Realise a $f$-normalised expression in the file system. */
void realise(Expr e);
/* Return a canonical textual representation of an expression. */
string printExpr(Expr e);

66
src/test.cc
View file

@ -11,13 +11,27 @@
#include "globals.hh"
void evalTest(Expr e)
typedef Expr (* Normaliser) (Expr);
void eval(Normaliser n, Expr e)
{
e = evalValue(e);
e = n(e);
cout << (string) hashExpr(e) << ": " << printExpr(e) << endl;
}
void evalFail(Normaliser n, Expr e)
{
try {
e = n(e);
abort();
} catch (Error e) {
cout << "error (expected): " << e.what() << endl;
}
}
struct MySink : DumpSink
{
virtual void operator () (const unsigned char * data, unsigned int len)
@ -90,19 +104,48 @@ void runTests()
/* Expression evaluation. */
evalTest(ATmake("Str(\"Hello World\")"));
evalTest(ATmake("Bool(True)"));
evalTest(ATmake("Bool(False)"));
evalTest(ATmake("App(Lam(\"x\", Var(\"x\")), Str(\"Hello World\"))"));
evalTest(ATmake("App(App(Lam(\"x\", Lam(\"y\", Var(\"x\"))), Str(\"Hello World\")), Str(\"Hallo Wereld\"))"));
evalTest(ATmake("App(Lam(\"sys\", Lam(\"x\", [Var(\"x\"), Var(\"sys\")])), Str(\"i686-suse-linux\"))"));
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 = hashFile(builder1fn);
string fn1 = nixValues + "/builder-1.sh";
Expr e1 = ATmake("File(<str>, ExtFile(<str>, <str>), [])",
fn1.c_str(),
builder1h.c_str(),
builder1fn.c_str());
eval(fNormalise, e1);
string fn2 = nixValues + "/refer.txt";
Expr e2 = ATmake("File(<str>, Regular(<str>), [<term>])",
fn2.c_str(),
("I refer to " + fn1).c_str(),
e1);
eval(fNormalise, e2);
realise(e2);
#if 0
Hash builder1 = addValue("./test-builder-1.sh");
Expr e1 = ATmake("Exec(Str(<str>), Hash(<str>), [])",
thisSystem.c_str(), ((string) builder1).c_str());
evalTest(e1);
eval(e1);
Hash builder2 = addValue("./test-builder-2.sh");
@ -110,14 +153,15 @@ void runTests()
"Exec(Str(<str>), Hash(<str>), [Tup(Str(\"src\"), <term>)])",
thisSystem.c_str(), ((string) builder2).c_str(), e1);
evalTest(e2);
eval(e2);
Hash h3 = addValue("./test-expr-1.nix");
Expr e3 = ATmake("Deref(Hash(<str>))", ((string) h3).c_str());
evalTest(e3);
eval(e3);
deleteValue(h3);
#endif
}