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#include "eval.hh"
#include "parser.hh"
#include "primops.hh"
EvalState::EvalState()
: normalForms(32768, 75)
{
blackHole = ATmake("BlackHole()");
if (!blackHole) throw Error("cannot build black hole");
nrEvaluated = nrCached = 0;
}
/* Substitute an argument set into the body of a function. */
static Expr substArgs(Expr body, ATermList formals, Expr arg)
{
ATMatcher m;
ATermMap subs;
Expr undefined = ATmake("Undefined");
/* Get the formal arguments. */
for (ATermIterator i(formals); i; ++i) {
Expr name, def;
if (atMatch(m, *i) >> "NoDefFormal" >> name)
subs.set(name, undefined);
else if (atMatch(m, *i) >> "DefFormal" >> name >> def)
subs.set(name, def);
else abort(); /* can't happen */
}
/* Get the actual arguments, and check that they match with the
formals. */
ATermMap args;
queryAllAttrs(arg, args);
for (ATermIterator i(args.keys()); i; ++i) {
Expr key = *i;
Expr cur = subs.get(key);
if (!cur)
throw badTerm(format("function has no formal argument `%1%'")
% aterm2String(key), arg);
subs.set(key, args.get(key));
}
/* Check that all arguments are defined. */
for (ATermIterator i(subs.keys()); i; ++i)
if (subs.get(*i) == undefined)
throw badTerm(format("formal argument `%1%' missing")
% aterm2String(*i), 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)
{
ATMatcher m;
/* Create the substitution list. */
ATermMap subs;
for (ATermIterator i(bnds); i; ++i) {
string s;
Expr e2;
if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
abort(); /* can't happen */
subs.set(s, ATmake("Select(<term>, <str>)", e, s.c_str()));
}
/* Create the non-recursive set. */
ATermMap as;
for (ATermIterator i(bnds); i; ++i) {
string s;
Expr e2;
if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
abort(); /* can't happen */
as.set(s, substitute(subs, e2));
}
return makeAttrs(as);
}
string evalString(EvalState & state, Expr e)
{
e = evalExpr(state, e);
ATMatcher m;
string s;
if (!(atMatch(m, e) >> "Str" >> s))
throw badTerm("string expected", e);
return s;
}
Path evalPath(EvalState & state, Expr e)
{
e = evalExpr(state, e);
ATMatcher m;
string s;
if (!(atMatch(m, e) >> "Path" >> s))
throw badTerm("path expected", e);
return s;
}
bool evalBool(EvalState & state, Expr e)
{
e = evalExpr(state, e);
ATMatcher m;
if (atMatch(m, e) >> "Bool" >> "True") return true;
else if (atMatch(m, e) >> "Bool" >> "False") return false;
else throw badTerm("expecting a boolean", e);
}
Expr evalExpr2(EvalState & state, Expr e)
{
ATMatcher m;
Expr e1, e2, e3, e4;
string s1;
/* Normal forms. */
if (atMatch(m, e) >> "Str" ||
atMatch(m, e) >> "Path" ||
atMatch(m, e) >> "Uri" ||
atMatch(m, e) >> "Bool" ||
atMatch(m, e) >> "Function" ||
atMatch(m, e) >> "Attrs" ||
atMatch(m, e) >> "List")
return e;
/* Any encountered variables must be undeclared or primops. */
if (atMatch(m, e) >> "Var" >> s1) {
if (s1 == "null") return primNull(state);
return e;
}
/* Function application. */
if (atMatch(m, e) >> "Call" >> e1 >> e2) {
ATermList formals;
/* Evaluate the left-hand side. */
e1 = evalExpr(state, e1);
/* Is it a primop or a function? */
if (atMatch(m, e1) >> "Var" >> s1) {
if (s1 == "import") return primImport(state, e2);
if (s1 == "derivation") return primDerivation(state, e2);
if (s1 == "toString") return primToString(state, e2);
if (s1 == "baseNameOf") return primBaseNameOf(state, e2);
if (s1 == "isNull") return primIsNull(state, e2);
else throw badTerm("undefined variable/primop", e1);
}
else if (atMatch(m, e1) >> "Function" >> formals >> e4)
return evalExpr(state,
substArgs(e4, formals, evalExpr(state, e2)));
else throw badTerm("expecting a function or primop", e1);
}
/* Attribute selection. */
if (atMatch(m, e) >> "Select" >> e1 >> s1) {
Expr a = queryAttr(evalExpr(state, e1), s1);
if (!a) throw badTerm(format("missing attribute `%1%'") % s1, e);
return evalExpr(state, a);
}
/* Mutually recursive sets. */
ATermList bnds;
if (atMatch(m, e) >> "Rec" >> bnds)
return expandRec(e, bnds);
/* Let expressions `let {..., body = ...}' are just desugared
into `(rec {..., body = ...}).body'. */
if (atMatch(m, e) >> "LetRec" >> bnds)
return evalExpr(state, ATmake("Select(Rec(<term>), \"body\")", bnds));
/* Conditionals. */
if (atMatch(m, e) >> "If" >> e1 >> e2 >> e3) {
if (evalBool(state, e1))
return evalExpr(state, e2);
else
return evalExpr(state, e3);
}
/* Assertions. */
if (atMatch(m, e) >> "Assert" >> e1 >> e2) {
if (!evalBool(state, e1)) throw badTerm("guard failed", e);
return evalExpr(state, e2);
}
/* Generic equality. */
if (atMatch(m, e) >> "OpEq" >> e1 >> e2)
return makeBool(evalExpr(state, e1) == evalExpr(state, e2));
/* Generic inequality. */
if (atMatch(m, e) >> "OpNEq" >> e1 >> e2)
return makeBool(evalExpr(state, e1) != evalExpr(state, e2));
/* Negation. */
if (atMatch(m, e) >> "OpNot" >> e1)
return makeBool(!evalBool(state, e1));
/* Implication. */
if (atMatch(m, e) >> "OpImpl" >> e1 >> e2)
return makeBool(!evalBool(state, e1) || evalBool(state, e2));
/* Conjunction (logical AND). */
if (atMatch(m, e) >> "OpAnd" >> e1 >> e2)
return makeBool(evalBool(state, e1) && evalBool(state, e2));
/* Disjunction (logical OR). */
if (atMatch(m, e) >> "OpOr" >> e1 >> e2)
return makeBool(evalBool(state, e1) || evalBool(state, e2));
/* Barf. */
throw badTerm("invalid expression", e);
}
Expr evalExpr(EvalState & state, Expr e)
{
startNest(nest, lvlVomit,
format("evaluating expression: %1%") % e);
state.nrEvaluated++;
/* Consult the memo table to quickly get the normal form of
previously evaluated expressions. */
Expr nf = state.normalForms.get(e);
if (nf) {
if (nf == state.blackHole)
throw badTerm("infinite recursion", e);
state.nrCached++;
return nf;
}
/* Otherwise, evaluate and memoize. */
state.normalForms.set(e, state.blackHole);
nf = evalExpr2(state, e);
state.normalForms.set(e, nf);
return nf;
}
Expr evalFile(EvalState & state, const Path & path)
{
startNest(nest, lvlTalkative, format("evaluating file `%1%'") % 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));
}
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