* Working evaluator.

* Mutually recursive attribute sets.
* Print evaluator efficiency statistics.

src/fix-ng/eval.cc

@@ -1,18 +1,167 @@
 #include "eval.hh"
 #include "expr.hh"
 #include "parser.hh"
+#include "primops.hh"
 
 
 EvalState::EvalState()
 {
     blackHole = ATmake("BlackHole()");
     if (!blackHole) throw Error("cannot build black hole");
+    nrEvaluated = nrCached = 0;
+}
+
+
+Expr getAttr(EvalState & state, Expr e, const string & name)
+{
+}
+
+
+/* Substitute an argument set into the body of a function. */
+static Expr substArgs(Expr body, ATermList formals, Expr arg)
+{
+    Subs subs;
+    Expr undefined = ATmake("Undefined");
+
+    /* Get the formal arguments. */
+    while (!ATisEmpty(formals)) {
+        char * s;
+        if (!ATmatch(ATgetFirst(formals), "<str>", &s))
+            abort(); /* can't happen */
+        subs[s] = undefined;
+        formals = ATgetNext(formals);
+    }
+
+    /* Get the actual arguments, and check that they match with the
+       formals. */
+    Attrs args;
+    queryAllAttrs(arg, args);
+    for (Attrs::iterator i = args.begin(); i != args.end(); i++) {
+        if (subs.find(i->first) == subs.end())
+            throw badTerm(format("argument `%1%' not declared") % i->first, arg);
+        subs[i->first] = i->second;
+    }
+
+    /* Check that all arguments are defined. */
+    for (Subs::iterator i = subs.begin(); i != subs.end(); i++)
+        if (i->second == undefined)
+            throw badTerm(format("formal argument `%1%' missing") % i->first, arg);
+    
+    return substitute(subs, body);
+}
+
+
+/* Transform a mutually recursive set into a non-recursive set.  Each
+   attribute is transformed into an expression that has all references
+   to attributes substituted with selection expressions on the
+   original set.  E.g., e = `rec {x = f x y, y = x}' becomes `{x = f
+   (e.x) (e.y), y = e.x}'. */
+ATerm expandRec(ATerm e, ATermList bnds)
+{
+    /* Create the substitution list. */
+    Subs subs;
+    ATermList bs = bnds;
+    while (!ATisEmpty(bs)) {
+        char * s;
+        Expr e2;
+        if (!ATmatch(ATgetFirst(bs), "Bind(<str>, <term>)", &s, &e2))
+            abort(); /* can't happen */
+        subs[s] = ATmake("Select(<term>, <str>)", e, s);
+        bs = ATgetNext(bs);
+    }
+
+    /* Create the non-recursive set. */
+    Attrs as;
+    bs = bnds;
+    while (!ATisEmpty(bs)) {
+        char * s;
+        Expr e2;
+        if (!ATmatch(ATgetFirst(bs), "Bind(<str>, <term>)", &s, &e2))
+            abort(); /* can't happen */
+        as[s] = substitute(subs, e2);
+        bs = ATgetNext(bs);
+    }
+
+    return makeAttrs(as);
+}
+
+
+string evalString(EvalState & state, Expr e)
+{
+    e = evalExpr(state, e);
+    char * s;
+    if (!ATmatch(e, "Str(<str>)", &s))
+        throw badTerm("string expected", e);
+    return s;
+}
+
+
+Path evalPath(EvalState & state, Expr e)
+{
+    e = evalExpr(state, e);
+    char * s;
+    if (!ATmatch(e, "Path(<str>)", &s))
+        throw badTerm("path expected", e);
+    return s;
 }
 
 
 Expr evalExpr2(EvalState & state, Expr e)
 {
-    return e;
+    Expr e1, e2, e3, e4;
+    char * s1;
+
+    /* Normal forms. */
+    if (ATmatch(e, "Str(<str>)", &s1) ||
+        ATmatch(e, "Path(<str>)", &s1) ||
+        ATmatch(e, "Uri(<str>)", &s1) ||
+        ATmatch(e, "Function([<list>], <term>)", &e1, &e2) ||
+        ATmatch(e, "Attrs([<list>])", &e1) ||
+        ATmatch(e, "List([<list>])", &e1))
+        return e;
+
+    /* Any encountered variables must be undeclared or primops. */
+    if (ATmatch(e, "Var(<str>)", &s1)) {
+        return e;
+    }
+
+    /* Function application. */
+    if (ATmatch(e, "Call(<term>, <term>)", &e1, &e2)) {
+        
+        /* Evaluate the left-hand side. */
+        e1 = evalExpr(state, e1);
+
+        /* Is it a primop or a function? */
+        if (ATmatch(e1, "Var(<str>)", &s1)) {
+            string primop(s1);
+            if (primop == "import") return primImport(state, e2);
+            if (primop == "derivation") return primDerivation(state, e2);
+            else throw badTerm("undefined variable/primop", e1);
+        }
+
+        else if (ATmatch(e1, "Function([<list>], <term>)", &e3, &e4)) {
+            return evalExpr(state, 
+                substArgs(e4, (ATermList) e3, evalExpr(state, e2)));
+        }
+        
+        else throw badTerm("expecting a function or primop", e1);
+    }
+
+    /* Attribute selection. */
+    if (ATmatch(e, "Select(<term>, <str>)", &e1, &s1)) {
+        string name(s1);
+        Expr a = queryAttr(evalExpr(state, e1), name);
+        if (!a) throw badTerm(format("missing attribute `%1%'") % name, e);
+        return evalExpr(state, a);
+    }
+
+    /* Mutually recursive sets. */
+    ATermList bnds;
+    if (ATmatch(e, "Rec([<list>])", &bnds))
+        return expandRec(e, (ATermList) bnds);
+
+    /* Barf. */
+    throw badTerm("invalid expression", e);
 }
 
 
@@ -20,12 +169,15 @@ Expr evalExpr(EvalState & state, Expr e)
 {
     Nest nest(lvlVomit, format("evaluating expression: %1%") % printTerm(e));
 
+    state.nrEvaluated++;
+
     /* Consult the memo table to quickly get the normal form of
        previously evaluated expressions. */
     NormalForms::iterator i = state.normalForms.find(e);
     if (i != state.normalForms.end()) {
         if (i->second == state.blackHole)
             throw badTerm("infinite recursion", e);
+        state.nrCached++;
         return i->second;
     }
 
@@ -43,3 +195,11 @@ Expr evalFile(EvalState & state, const Path & path)
     Expr e = parseExprFromFile(path);
     return evalExpr(state, e);
 }
+
+
+void printEvalStats(EvalState & state)
+{
+    debug(format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency")
+        % state.nrEvaluated % state.nrCached
+        % ((float) state.nrCached / (float) state.nrEvaluated * 100));
+}