267 lines
7.5 KiB
C++
267 lines
7.5 KiB
C++
#include "eval.hh"
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#include "expr.hh"
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#include "parser.hh"
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#include "primops.hh"
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EvalState::EvalState()
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: normalForms(32768, 75)
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{
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blackHole = ATmake("BlackHole()");
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if (!blackHole) throw Error("cannot build black hole");
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nrEvaluated = nrCached = 0;
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}
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/* Substitute an argument set into the body of a function. */
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static Expr substArgs(Expr body, ATermList formals, Expr arg)
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{
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ATMatcher m;
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ATermMap subs;
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Expr undefined = ATmake("Undefined");
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/* Get the formal arguments. */
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for (ATermIterator i(formals); i; ++i) {
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Expr name, def;
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if (atMatch(m, *i) >> "NoDefFormal" >> name)
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subs.set(name, undefined);
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else if (atMatch(m, *i) >> "DefFormal" >> name >> def)
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subs.set(name, def);
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else abort(); /* can't happen */
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}
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/* Get the actual arguments, and check that they match with the
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formals. */
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ATermMap args;
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queryAllAttrs(arg, args);
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for (ATermIterator i(args.keys()); i; ++i) {
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Expr key = *i;
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Expr cur = subs.get(key);
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if (!cur)
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throw badTerm(format("function has no formal argument `%1%'")
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% aterm2String(key), arg);
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subs.set(key, args.get(key));
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}
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/* Check that all arguments are defined. */
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for (ATermIterator i(subs.keys()); i; ++i)
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if (subs.get(*i) == undefined)
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throw badTerm(format("formal argument `%1%' missing")
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% aterm2String(*i), arg);
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return substitute(subs, body);
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}
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/* Transform a mutually recursive set into a non-recursive set. Each
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attribute is transformed into an expression that has all references
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to attributes substituted with selection expressions on the
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original set. E.g., e = `rec {x = f x y, y = x}' becomes `{x = f
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(e.x) (e.y), y = e.x}'. */
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ATerm expandRec(ATerm e, ATermList bnds)
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{
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ATMatcher m;
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/* Create the substitution list. */
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ATermMap subs;
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for (ATermIterator i(bnds); i; ++i) {
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string s;
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Expr e2;
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if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
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abort(); /* can't happen */
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subs.set(s, ATmake("Select(<term>, <str>)", e, s.c_str()));
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}
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/* Create the non-recursive set. */
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ATermMap as;
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for (ATermIterator i(bnds); i; ++i) {
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string s;
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Expr e2;
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if (!(atMatch(m, *i) >> "Bind" >> s >> e2))
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abort(); /* can't happen */
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as.set(s, substitute(subs, e2));
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}
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return makeAttrs(as);
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}
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string evalString(EvalState & state, Expr e)
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{
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e = evalExpr(state, e);
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ATMatcher m;
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string s;
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if (!(atMatch(m, e) >> "Str" >> s))
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throw badTerm("string expected", e);
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return s;
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}
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Path evalPath(EvalState & state, Expr e)
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{
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e = evalExpr(state, e);
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ATMatcher m;
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string s;
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if (!(atMatch(m, e) >> "Path" >> s))
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throw badTerm("path expected", e);
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return s;
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}
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bool evalBool(EvalState & state, Expr e)
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{
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e = evalExpr(state, e);
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ATMatcher m;
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if (atMatch(m, e) >> "Bool" >> "True") return true;
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else if (atMatch(m, e) >> "Bool" >> "False") return false;
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else throw badTerm("expecting a boolean", e);
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}
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Expr evalExpr2(EvalState & state, Expr e)
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{
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ATMatcher m;
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Expr e1, e2, e3, e4;
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string s1;
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/* Normal forms. */
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if (atMatch(m, e) >> "Str" ||
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atMatch(m, e) >> "Path" ||
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atMatch(m, e) >> "Uri" ||
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atMatch(m, e) >> "Bool" ||
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atMatch(m, e) >> "Function" ||
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atMatch(m, e) >> "Attrs" ||
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atMatch(m, e) >> "List")
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return e;
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/* Any encountered variables must be undeclared or primops. */
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if (atMatch(m, e) >> "Var" >> s1) {
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if (s1 == "null") return primNull(state);
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return e;
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}
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/* Function application. */
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if (atMatch(m, e) >> "Call" >> e1 >> e2) {
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ATermList formals;
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/* Evaluate the left-hand side. */
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e1 = evalExpr(state, e1);
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/* Is it a primop or a function? */
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if (atMatch(m, e1) >> "Var" >> s1) {
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if (s1 == "import") return primImport(state, e2);
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if (s1 == "derivation") return primDerivation(state, e2);
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if (s1 == "toString") return primToString(state, e2);
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if (s1 == "baseNameOf") return primBaseNameOf(state, e2);
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if (s1 == "isNull") return primIsNull(state, e2);
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else throw badTerm("undefined variable/primop", e1);
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}
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else if (atMatch(m, e1) >> "Function" >> formals >> e4)
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return evalExpr(state,
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substArgs(e4, formals, evalExpr(state, e2)));
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else throw badTerm("expecting a function or primop", e1);
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}
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/* Attribute selection. */
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if (atMatch(m, e) >> "Select" >> e1 >> s1) {
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Expr a = queryAttr(evalExpr(state, e1), s1);
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if (!a) throw badTerm(format("missing attribute `%1%'") % s1, e);
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return evalExpr(state, a);
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}
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/* Mutually recursive sets. */
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ATermList bnds;
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if (atMatch(m, e) >> "Rec" >> bnds)
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return expandRec(e, bnds);
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/* Let expressions `let {..., body = ...}' are just desugared
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into `(rec {..., body = ...}).body'. */
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if (atMatch(m, e) >> "LetRec" >> bnds)
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return evalExpr(state, ATmake("Select(Rec(<term>), \"body\")", bnds));
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/* Conditionals. */
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if (atMatch(m, e) >> "If" >> e1 >> e2 >> e3) {
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if (evalBool(state, e1))
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return evalExpr(state, e2);
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else
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return evalExpr(state, e3);
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}
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/* Assertions. */
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if (atMatch(m, e) >> "Assert" >> e1 >> e2) {
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if (!evalBool(state, e1)) throw badTerm("guard failed", e);
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return evalExpr(state, e2);
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}
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/* Generic equality. */
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if (atMatch(m, e) >> "OpEq" >> e1 >> e2)
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return makeBool(evalExpr(state, e1) == evalExpr(state, e2));
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/* Generic inequality. */
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if (atMatch(m, e) >> "OpNEq" >> e1 >> e2)
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return makeBool(evalExpr(state, e1) != evalExpr(state, e2));
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/* Negation. */
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if (atMatch(m, e) >> "OpNot" >> e1)
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return makeBool(!evalBool(state, e1));
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/* Implication. */
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if (atMatch(m, e) >> "OpImpl" >> e1 >> e2)
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return makeBool(!evalBool(state, e1) || evalBool(state, e2));
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/* Conjunction (logical AND). */
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if (atMatch(m, e) >> "OpAnd" >> e1 >> e2)
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return makeBool(evalBool(state, e1) && evalBool(state, e2));
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/* Disjunction (logical OR). */
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if (atMatch(m, e) >> "OpOr" >> e1 >> e2)
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return makeBool(evalBool(state, e1) || evalBool(state, e2));
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/* Barf. */
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throw badTerm("invalid expression", e);
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}
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Expr evalExpr(EvalState & state, Expr e)
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{
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startNest(nest, lvlVomit,
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format("evaluating expression: %1%") % e);
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state.nrEvaluated++;
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/* Consult the memo table to quickly get the normal form of
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previously evaluated expressions. */
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Expr nf = state.normalForms.get(e);
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if (nf) {
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if (nf == state.blackHole)
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throw badTerm("infinite recursion", e);
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state.nrCached++;
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return nf;
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}
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/* Otherwise, evaluate and memoize. */
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state.normalForms.set(e, state.blackHole);
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nf = evalExpr2(state, e);
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state.normalForms.set(e, nf);
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return nf;
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}
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Expr evalFile(EvalState & state, const Path & path)
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{
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startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
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Expr e = parseExprFromFile(path);
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return evalExpr(state, e);
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}
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void printEvalStats(EvalState & state)
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{
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debug(format("evaluated %1% expressions, %2% cache hits, %3%%% efficiency")
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% state.nrEvaluated % state.nrCached
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% ((float) state.nrCached / (float) state.nrEvaluated * 100));
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}
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