* Evaluate lets directly (i.e. without desugaring to `rec { attrs...;
<let-body> = e; }.<let-body>). This prevents the unnecessary allocation of an attribute set.
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@ -456,6 +456,31 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
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}
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void ExprLet::eval(EvalState & state, Env & env, Value & v)
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{
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/* Create a new environment that contains the attributes in this
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`let'. */
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Env & env2(state.allocEnv());
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env2.up = &env;
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/* The recursive attributes are evaluated in the new
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environment. */
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foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs) {
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Value & v2 = env2.bindings[i->first];
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mkThunk(v2, env2, i->second);
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}
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/* The inherited attributes, on the other hand, are evaluated in
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the original environment. */
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foreach (list<Symbol>::iterator, i, attrs->inherited) {
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Value & v2 = env2.bindings[*i];
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mkCopy(v2, *state.lookupVar(&env, *i));
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}
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state.eval(env2, body, v);
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}
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void ExprList::eval(EvalState & state, Env & env, Value & v)
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{
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state.mkList(v, elems.size());
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@ -244,6 +244,7 @@ private:
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friend class ExprVar;
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friend class ExprAttrs;
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friend class ExprLet;
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public:
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@ -87,6 +87,16 @@ void ExprLambda::show(std::ostream & str)
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str << ": " << *body << ")";
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}
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void ExprLet::show(std::ostream & str)
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{
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str << "let ";
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foreach (list<Symbol>::iterator, i, attrs->inherited)
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str << "inherit " << *i << "; ";
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foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
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str << i->first << " = " << *i->second << "; ";
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str << "in " << *body;
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}
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void ExprWith::show(std::ostream & str)
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{
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str << "with " << *attrs << "; " << *body;
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@ -139,6 +139,14 @@ struct ExprLambda : Expr
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COMMON_METHODS
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};
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struct ExprLet : Expr
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{
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ExprAttrs * attrs;
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Expr * body;
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ExprLet(ExprAttrs * attrs, Expr * body) : attrs(attrs), body(body) { };
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COMMON_METHODS
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};
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struct ExprWith : Expr
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{
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Pos pos;
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@ -306,7 +306,7 @@ expr_function
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| WITH expr ';' expr_function
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{ $$ = new ExprWith(CUR_POS, $2, $4); }
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| LET binds IN expr_function
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{ $2->attrs[data->sLetBody] = $4; $2->recursive = true; $$ = new ExprSelect($2, data->sLetBody); }
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{ $$ = new ExprLet($2, $4); }
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| expr_if
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;
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