Files
lix/lix/libexpr/nixexpr.hh
T
Qyriad 2806613954 libexpr: refactor ExprSelect::eval
Change-Id: Ibb21dbd3c25649b3b301bc7baaa52a8aa938ebe0
2025-11-07 14:54:02 +01:00

666 lines
23 KiB
C++

#pragma once
///@file
#include <map>
#include <memory>
#include <vector>
#include "lix/libexpr/value.hh"
#include "lix/libexpr/symbol-table.hh"
#include "lix/libutil/json.hh"
#include "lix/libexpr/eval-error.hh"
#include "lix/libexpr/pos-idx.hh"
#include "lix/libutil/strings.hh"
#include "lix/libutil/linear-map.hh"
namespace nix {
struct Env;
struct Value;
class Evaluator;
struct ExprWith;
struct StaticEnv;
/**
* An attribute path is a sequence of attribute names.
*/
struct AttrName
{
PosIdx pos;
Symbol symbol;
std::unique_ptr<Expr> expr;
AttrName(PosIdx pos, Symbol s);
AttrName(PosIdx pos, std::unique_ptr<Expr> e);
};
typedef std::vector<AttrName> AttrPath;
std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath);
JSON printAttrPathToJson(const SymbolTable & symbols, const AttrPath & attrPath);
/* Abstract syntax of Nix expressions. */
struct ExprDebugFrame;
struct ExprLiteral;
struct ExprString;
struct ExprPath;
struct ExprVar;
struct ExprInheritFrom;
struct ExprSelect;
struct ExprOpHasAttr;
struct ExprSet;
struct ExprList;
struct ExprLambda;
struct ExprCall;
struct ExprLet;
struct ExprWith;
struct ExprIf;
struct ExprAssert;
struct ExprOpNot;
struct ExprOpEq;
struct ExprOpNEq;
struct ExprOpAnd;
struct ExprOpOr;
struct ExprOpImpl;
struct ExprOpUpdate;
struct ExprOpConcatLists;
struct ExprConcatStrings;
struct ExprPos;
struct ExprBlackHole;
struct ExprVisitor
{
virtual void visit(ExprDebugFrame & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprLiteral & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprVar & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprInheritFrom & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprSelect & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpHasAttr & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprSet & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprList & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprLambda & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprCall & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprLet & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprWith & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprIf & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprAssert & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpNot & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpEq & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpNEq & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpAnd & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpOr & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpImpl & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpUpdate & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprOpConcatLists & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprConcatStrings & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprPos & e, std::unique_ptr<Expr> & ptr) = 0;
virtual void visit(ExprBlackHole & e, std::unique_ptr<Expr> & ptr) = 0;
void visit(std::unique_ptr<Expr> & ptr);
};
struct Expr
{
protected:
Expr(Expr &&) = default;
Expr & operator=(Expr &&) = default;
Expr(const PosIdx pos) : pos(pos) {};
public:
struct AstSymbols {
Symbol sub, lessThan, mul, div, or_, findFile, nixPath, body, overrides;
};
PosIdx pos;
Expr() = default;
Expr(const Expr &) = delete;
Expr & operator=(const Expr &) = delete;
virtual ~Expr() { };
static std::unique_ptr<Expr> finalize(
std::unique_ptr<Expr> parsed, Evaluator & es, const std::shared_ptr<const StaticEnv> & env
);
virtual JSON toJSON(const SymbolTable & symbols) const;
virtual void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) = 0;
virtual void eval(EvalState & state, Env & env, Value & v);
virtual Value maybeThunk(EvalState & state, Env & env);
virtual void setName(Symbol name);
PosIdx getPos() const { return pos; }
template<typename E>
E & cast()
{
return dynamic_cast<E &>(*this);
}
template<typename E>
E * try_cast()
{
return dynamic_cast<E *>(this);
}
};
inline void ExprVisitor::visit(std::unique_ptr<Expr> & ptr)
{
ptr->accept(*this, ptr);
}
struct ExprDebugFrame : Expr
{
std::unique_ptr<Expr> inner;
std::string message;
ExprDebugFrame(PosIdx pos, std::unique_ptr<Expr> inner, std::string message)
: Expr(pos)
, inner(std::move(inner))
, message(std::move(message))
{
}
JSON toJSON(const SymbolTable & symbols) const override
{
return inner->toJSON(symbols);
}
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprLiteral : Expr
{
protected:
Value v;
ExprLiteral(const PosIdx pos) : Expr(pos) {};
public:
Value maybeThunk(EvalState & state, Env & env) override;
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprInt : ExprLiteral
{
Value::Int i;
ExprInt(const PosIdx pos, NixInt n) : ExprLiteral(pos), i{{Value::Acb::tInt}, n}
{
v = Value::isTaggableInteger(n) ? Value{NewValueAs::integer, n} : Value(i);
}
ExprInt(const PosIdx pos, NixInt::Inner n) : ExprInt(pos, NixInt(n)) {}
};
struct ExprFloat : ExprLiteral
{
Value::Float f;
ExprFloat(const PosIdx pos, NewValueAs::floating_t, double f)
: ExprLiteral(pos)
, f{{Value::Acb::tFloat}, f}
{
v = Value(this->f);
}
};
struct ExprString : ExprLiteral
{
std::unique_ptr<Value::Str, Value::Str::Deleter> contents;
Value::String strcb{.content = contents.get(), .context = nullptr};
ExprString(const PosIdx pos, std::string s) : ExprLiteral(pos), contents(Value::Str::copy(s))
{
v = {NewValueAs::string, &strcb};
}
std::string_view str() const
{
return contents->str();
}
};
struct ExprPath : ExprLiteral
{
std::unique_ptr<Value::Str, Value::Str::Deleter> contents;
Value::String strcb{.content = contents.get(), .context = Value::String::path};
ExprPath(const PosIdx pos, std::string s) : ExprLiteral(pos), contents(Value::Str::copy(s))
{
v = Value{NewValueAs::path, &strcb};
}
std::string_view str() const
{
return contents->str();
}
};
typedef uint32_t Level;
typedef uint32_t Displacement;
struct ExprVar : Expr
{
Symbol name;
/* Whether the variable comes from an environment (e.g. a rec, let
or function argument) or from a "with".
`nullptr`: Not from a `with`.
Valid pointer: the nearest, innermost `with` expression to query first. */
ExprWith * fromWith;
/* In the former case, the value is obtained by going `level`
levels up from the current environment and getting the
`displ`th value in that environment. In the latter case, the
value is obtained by getting the attribute named `name` from
the set stored in the environment that is `level` levels up
from the current one.*/
Level level;
Displacement displ;
/* Variables like `__sub` as generated from expressions like `5 - 3` shouldn't be overridden.
* This is implemented by having a blessed "root" env that contains the definitions (usually `builtins`)
* and checking that this var only binds against that env.
*/
bool needsRoot;
ExprVar(Symbol name) : name(name), needsRoot(false) { };
ExprVar(const PosIdx & pos, Symbol name, bool needsRoot = false) : Expr(pos), name(name), needsRoot(needsRoot) { };
Value maybeThunk(EvalState & state, Env & env) override;
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
/**
* A pseudo-expression for the purpose of evaluating the `from` expression in `inherit (from)` syntax.
* Unlike normal variable references, the displacement is set during parsing, and always refers to
* `ExprAttrs::inheritFromExprs` (by itself or in `ExprLet`), whose values are put into their own `Env`.
*/
struct ExprInheritFrom : Expr
{
Expr & fromExpr;
Displacement displ;
ExprInheritFrom(PosIdx pos, Displacement displ, Expr & fromExpr)
: Expr(pos), fromExpr(fromExpr), displ(displ)
{
}
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct Attr;
struct ExprSelect : Expr
{
/** The expression attributes are being selected on. e.g. `foo` in `foo.bar.baz`. */
std::unique_ptr<Expr> e;
/** A default value specified with `or`, if the selected attr doesn't exist.
* e.g. `bix` in `foo.bar.baz or bix`
*/
std::unique_ptr<Expr> def;
/** The path of attributes being selected. e.g. `bar.baz` in `foo.bar.baz.` */
AttrPath attrPath;
ExprSelect(const PosIdx & pos, std::unique_ptr<Expr> e, AttrPath attrPath, std::unique_ptr<Expr> def) : Expr(pos), e(std::move(e)), def(std::move(def)), attrPath(std::move(attrPath)) { };
ExprSelect(const PosIdx & pos, std::unique_ptr<Expr> e, const PosIdx namePos, Symbol name) : Expr(pos), e(std::move(e)) { attrPath.push_back(AttrName(namePos, name)); };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
private:
Attr const * selectSingleAttr(EvalState & state, Env & env, AttrName const & attrName, Value & vCurrent);
};
struct ExprOpHasAttr : Expr
{
std::unique_ptr<Expr> e;
AttrPath attrPath;
ExprOpHasAttr(const PosIdx & pos, std::unique_ptr<Expr> e, AttrPath attrPath) : Expr(pos), e(std::move(e)), attrPath(std::move(attrPath)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
/* Helper struct to contain the data shared across lets and sets */
struct ExprAttrs
{
ExprAttrs() = default;
ExprAttrs(const ExprAttrs &) = delete;
ExprAttrs & operator=(const ExprAttrs &) = delete;
ExprAttrs(ExprAttrs &&) = default;
ExprAttrs & operator=(ExprAttrs &&) = default;
virtual ~ExprAttrs() = default;
struct AttrDef {
enum class Kind {
/** `attr = expr;` */
Plain,
/** `inherit attr1 attrn;` */
Inherited,
/** `inherit (expr) attr1 attrn;` */
InheritedFrom,
};
Kind kind;
std::unique_ptr<Expr> e;
PosIdx pos;
Displacement displ; // displacement
AttrDef(std::unique_ptr<Expr> e, const PosIdx & pos, Kind kind = Kind::Plain)
: kind(kind), e(std::move(e)), pos(pos) { };
AttrDef() { };
template<typename T>
T chooseByKind(const T & plain, const T & inherited, const T & inheritedFrom) const
{
switch (kind) {
case Kind::Plain:
return plain;
case Kind::Inherited:
return inherited;
default:
case Kind::InheritedFrom:
return inheritedFrom;
}
}
};
typedef std::map<Symbol, AttrDef> AttrDefs;
AttrDefs attrs;
std::unique_ptr<std::list<std::unique_ptr<Expr>>> inheritFromExprs;
struct DynamicAttrDef {
std::unique_ptr<Expr> nameExpr, valueExpr;
PosIdx pos;
DynamicAttrDef(std::unique_ptr<Expr> nameExpr, std::unique_ptr<Expr> valueExpr, const PosIdx & pos)
: nameExpr(std::move(nameExpr)), valueExpr(std::move(valueExpr)), pos(pos) { };
};
typedef std::vector<DynamicAttrDef> DynamicAttrDefs;
DynamicAttrDefs dynamicAttrs;
std::shared_ptr<const StaticEnv> buildRecursiveEnv(const std::shared_ptr<const StaticEnv> & env);
std::shared_ptr<const StaticEnv> bindInheritSources(ExprVisitor & e, const StaticEnv & env);
Env * buildInheritFromEnv(EvalState & state, Env & up);
void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const;
};
struct ExprSet : Expr, ExprAttrs {
bool recursive = false;
ExprSet(const PosIdx &pos, bool recursive = false) : Expr(pos), recursive(recursive) { };
ExprSet() { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprReplBindings {
std::map<Symbol, std::unique_ptr<Expr>> symbols;
void finalize(Evaluator & es, const std::shared_ptr<const StaticEnv> & env) {
for (auto & [_, e] : symbols)
e = Expr::finalize(std::move(e), es, env);
}
};
struct ExprList : Expr
{
std::vector<std::unique_ptr<Expr>> elems;
ExprList(PosIdx pos) : Expr(pos) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
Value maybeThunk(EvalState & state, Env & env) override;
};
struct Pattern {
/** The argument name of this particular lambda. Is a falsey symbol if there
* is no such argument. */
Symbol name;
Pattern() = default;
explicit Pattern(Symbol name) : name(name) { }
virtual ~Pattern() = default;
virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) = 0;
virtual void accept(ExprVisitor & ev) = 0;
virtual Env &
match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) = 0;
virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const = 0;
};
/** A plain old lambda */
struct SimplePattern : Pattern
{
SimplePattern() = default;
SimplePattern(Symbol name) : Pattern(name) {
assert(name);
}
virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) override;
virtual void accept(ExprVisitor & ev) override;
virtual Env &
match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) override;
virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const override;
};
/** Attribute set destructuring in arguments of a lambda, if present */
struct AttrsPattern : Pattern
{
struct Formal
{
PosIdx pos;
Symbol name;
std::unique_ptr<Expr> def;
};
typedef std::vector<Formal> Formals_;
Formals_ formals;
bool ellipsis;
virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) override;
virtual void accept(ExprVisitor & ev) override;
virtual Env &
match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) override;
virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const override;
bool has(Symbol arg) const
{
auto it = std::lower_bound(formals.begin(), formals.end(), arg,
[] (const Formal & f, const Symbol & sym) { return f.name < sym; });
return it != formals.end() && it->name == arg;
}
std::vector<std::reference_wrapper<const Formal>> lexicographicOrder(const SymbolTable & symbols) const
{
std::vector<std::reference_wrapper<const Formal>> result(formals.begin(), formals.end());
std::sort(result.begin(), result.end(),
[&] (const Formal & a, const Formal & b) {
std::string_view sa = symbols[a.name], sb = symbols[b.name];
return sa < sb;
});
return result;
}
};
struct ExprLambda : Expr
{
/** Name of the lambda. This is set if the lambda is defined in a
* let-expression or an attribute set, such that there is a name.
* Lambdas may have a falsey symbol as the name if they are anonymous */
Symbol name;
std::unique_ptr<Pattern> pattern;
std::unique_ptr<Expr> body;
ExprLambda(PosIdx pos, std::unique_ptr<Pattern> pattern, std::unique_ptr<Expr> body)
: Expr(pos), pattern(std::move(pattern)), body(std::move(body))
{
}
void setName(Symbol name) override;
std::string showNamePos(const EvalState & state) const;
/** Returns the name of the lambda,
* or "anonymous lambda" if it doesn't have one.
*/
inline std::string_view getName(SymbolTable const & symbols) const
{
if (this->name) {
return symbols[this->name];
}
return "anonymous lambda";
}
/** Returns the name of the lambda in single quotes,
* or "anonymous lambda" if it doesn't have one.
*/
inline std::string getQuotedName(SymbolTable const & symbols) const
{
if (this->name) {
return concatStrings("'", symbols[this->name], "'");
}
return "anonymous lambda";
}
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprCall : Expr
{
std::unique_ptr<Expr> fun;
std::vector<std::unique_ptr<Expr>> args;
ExprCall(const PosIdx & pos, std::unique_ptr<Expr> fun, std::vector<std::unique_ptr<Expr>> && args)
: Expr(pos), fun(std::move(fun)), args(std::move(args))
{ }
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprLet : Expr, ExprAttrs
{
std::unique_ptr<Expr> body;
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprWith : Expr
{
std::unique_ptr<Expr> attrs, body;
size_t prevWith;
ExprWith * parentWith;
ExprWith(const PosIdx & pos, std::unique_ptr<Expr> attrs, std::unique_ptr<Expr> body) : Expr(pos), attrs(std::move(attrs)), body(std::move(body)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprIf : Expr
{
std::unique_ptr<Expr> cond, then, else_;
ExprIf(const PosIdx & pos, std::unique_ptr<Expr> cond, std::unique_ptr<Expr> then, std::unique_ptr<Expr> else_) : Expr(pos), cond(std::move(cond)), then(std::move(then)), else_(std::move(else_)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprAssert : Expr
{
std::unique_ptr<Expr> cond, body;
ExprAssert(const PosIdx & pos, std::unique_ptr<Expr> cond, std::unique_ptr<Expr> body) : Expr(pos), cond(std::move(cond)), body(std::move(body)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprOpNot : Expr
{
std::unique_ptr<Expr> e;
ExprOpNot(const PosIdx & pos, std::unique_ptr<Expr> e) : Expr(pos), e(std::move(e)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
#define MakeBinOp(name, s) \
struct name : Expr \
{ \
std::unique_ptr<Expr> e1, e2; \
name(std::unique_ptr<Expr> e1, std::unique_ptr<Expr> e2) : e1(std::move(e1)), e2(std::move(e2)) { }; \
name(const PosIdx & pos, std::unique_ptr<Expr> e1, std::unique_ptr<Expr> e2) : Expr(pos), e1(std::move(e1)), e2(std::move(e2)) { }; \
JSON toJSON(const SymbolTable & symbols) const override \
{ \
return { \
{"_type", #name}, \
{"e1", e1->toJSON(symbols)}, \
{"e2", e2->toJSON(symbols)} \
};\
} \
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); } \
void eval(EvalState & state, Env & env, Value & v) override; \
};
MakeBinOp(ExprOpEq, "==")
MakeBinOp(ExprOpNEq, "!=")
MakeBinOp(ExprOpAnd, "&&")
MakeBinOp(ExprOpOr, "||")
MakeBinOp(ExprOpImpl, "->")
MakeBinOp(ExprOpUpdate, "//")
MakeBinOp(ExprOpConcatLists, "++")
struct ExprConcatStrings : Expr
{
bool isInterpolation;
std::vector<std::pair<PosIdx, std::unique_ptr<Expr>>> es;
ExprConcatStrings(const PosIdx & pos, bool isInterpolation, std::vector<std::pair<PosIdx, std::unique_ptr<Expr>>> es)
: Expr(pos), isInterpolation(isInterpolation), es(std::move(es)) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
struct ExprPos : Expr
{
ExprPos(const PosIdx & pos) : Expr(pos) { };
JSON toJSON(const SymbolTable & symbols) const override;
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
/* only used to mark thunks as black holes. */
struct ExprBlackHole : Expr
{
void eval(EvalState & state, Env & env, Value & v) override;
void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
};
extern ExprBlackHole eBlackHole;
/* Static environments are used to map variable names onto (level,
displacement) pairs used to obtain the value of the variable at
runtime. */
struct StaticEnv
{
ExprWith * isWith;
const StaticEnv * up;
LinearMap<Symbol, Displacement> vars;
/* See ExprVar::needsRoot */
bool isRoot = false;
StaticEnv(ExprWith * isWith, const StaticEnv * up, size_t expectedSize = 0) : isWith(isWith), up(up) {
vars.reserve(expectedSize);
};
};
}