From 097ae971692f148963606fd80d55636a2f26ac32 Mon Sep 17 00:00:00 2001 From: Michael Dyck Date: Sun, 24 Jan 2021 00:30:29 -0500 Subject: [PATCH] Editorial: Model a binding as a Record --- spec.html | 179 ++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 153 insertions(+), 26 deletions(-) diff --git a/spec.html b/spec.html index b04d0c8bdeb..70e76cbfa2d 100644 --- a/spec.html +++ b/spec.html @@ -9819,15 +9819,101 @@

Declarative Environment Records

[[Bindings]] - List of bindings + List of DeclarativeBindingRecord - Satisfies the invariant that no two bindings in [[Bindings]] are bindings for the same name. + Satisfies the invariant that no two records in [[Bindings]] have the same [[BoundName]]. + +

A DeclarativeBindingRecord has the following fields:

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ Field Name + + Value + + Meaning +
+ [[BoundName]] + + a String + + the name being bound. +
+ [[IsInitialized]] + + a Boolean + + indicates whether the binding is initialized. +
+ [[BoundValue]] + + an ECMAScript language value + + the value that the name is bound to. +
+ [[IsMutable]] + + a Boolean + + if *true*, indicates that the binding is mutable. +
+ [[IsDeletable]] + + a Boolean + + if *true*, indicates that the binding may be deleted by a subsequent DeleteBinding call. +
+ [[IsStrict]] + + a Boolean + + if *true*, indicates that the binding is a strict binding. +
+ +

The behaviour of the concrete specification methods for declarative Environment Records is defined by the following algorithms.

@@ -9844,7 +9930,7 @@

It determines if the argument identifier is one of the identifiers bound by the record.
- 1. If _envRec_.[[Bindings]] contains a binding for the name that is the value of _N_, return *true*. + 1. If _envRec_.[[Bindings]] contains a DeclarativeBindingRecord whose [[BoundName]] field is equal to the value of _N_, return *true*. 1. Return *false*. @@ -9865,7 +9951,7 @@

1. Assert: _envRec_.HasBinding(_N_) is *false*. - 1. Let _binding_ be a mutable binding for _N_ and record that it is uninitialized. If _D_ is *true*, record that the newly created binding may be deleted by a subsequent DeleteBinding call. + 1. Let _binding_ be DeclarativeBindingRecord { [[BoundName]]: _N_, [[IsInitialized]]: *false*, [[BoundValue]]: *undefined*, [[IsMutable]]: *true*, [[IsDeletable]]: _D_, [[IsStrict]]: *false* }. 1. Append _binding_ to _envRec_.[[Bindings]]. 1. Return NormalCompletion(~empty~). @@ -9887,7 +9973,7 @@

1. Assert: _envRec_.HasBinding(_N_) is *false*. - 1. Let _binding_ be an immutable binding for _N_ and record that it is uninitialized. If _S_ is *true*, record that the newly created binding is a strict binding. + 1. Let _binding_ be DeclarativeBindingRecord { [[BoundName]]: _N_, [[IsInitialized]]: *false*, [[BoundValue]]: *undefined*, [[IsMutable]]: *false*, [[IsDeletable]]: *false*, [[IsStrict]]: _S_ }. 1. Append _binding_ to _envRec_.[[Bindings]]. 1. Return NormalCompletion(~empty~). @@ -9909,10 +9995,10 @@

1. Assert: _envRec_.HasBinding(_N_) is *true*. - 1. Let _binding_ be the binding for _N_ in _envRec_.[[Bindings]]. - 1. Assert: _binding_ is uninitialized. - 1. Set the bound value of _binding_ to _V_. - 1. Record that _binding_ has been initialized. + 1. Let _binding_ be the DeclarativeBindingRecord in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_. + 1. Assert: _binding_.[[IsInitialized]] is *false*. + 1. Set _binding_.[[BoundValue]] to _V_. + 1. Set _binding_.[[IsInitialized]] to *true*. 1. Return NormalCompletion(~empty~). @@ -9938,10 +10024,10 @@

1. Perform _envRec_.CreateMutableBinding(_N_, *true*). 1. Perform _envRec_.InitializeBinding(_N_, _V_). 1. Return NormalCompletion(~empty~). - 1. Let _binding_ be the binding for _N_ in _envRec_.[[Bindings]]. - 1. If _binding_ is a strict binding, set _S_ to *true*. - 1. If _binding_ has not yet been initialized, throw a *ReferenceError* exception. - 1. Else if _binding_ is a mutable binding, change its bound value to _V_. + 1. Let _binding_ be the DeclarativeBindingRecord in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_. + 1. If _binding_.[[IsStrict]] is *true*, set _S_ to *true*. + 1. If _binding_.[[IsInitialized]] is *false*, throw a *ReferenceError* exception. + 1. Else if _binding_.[[IsMutable]] is *true*, change its bound value to _V_. 1. Else, 1. Assert: This is an attempt to change the value of an immutable binding. 1. If _S_ is *true*, throw a *TypeError* exception. @@ -9969,9 +10055,9 @@

1. Assert: _envRec_.HasBinding(_N_) is *true*. - 1. Let _binding_ be the binding for _N_ in _envRec_.[[Bindings]]. - 1. If _binding_ is an uninitialized binding, throw a *ReferenceError* exception. - 1. Return the value currently bound in _binding_. + 1. Let _binding_ be the DeclarativeBindingRecord in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_. + 1. If _binding_.[[IsInitialized]] is *false*, throw a *ReferenceError* exception. + 1. Return _binding_.[[BoundValue]]. @@ -9990,8 +10076,8 @@

1. Assert: _envRec_.HasBinding(_N_) is *true*. - 1. Let _binding_ be the binding for _N_ in _envRec_.[[Bindings]]. - 1. If _binding_ cannot be deleted, return *false*. + 1. Let _binding_ be the DeclarativeBindingRecord in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_. + 1. If _binding_.[[IsDeletable]] is *false*, return *false*. 1. Remove _binding_ from _envRec_.[[Bindings]]. 1. Return *true*. @@ -11012,6 +11098,46 @@

Module Environment Records

+

The [[Bindings]] of a Module Environment Record can include ImportDeclarativeBindingRecords. These have all the fields of DeclarativeBindingRecords, plus the additional state fields listed in the following table.

+ + + + + + + + + + + + + + + + + + + +
+ Field Name + + Value + + Meaning +
+ [[TargetModuleRec]] + + a Module Record + + ? +
+ [[TargetName]] + + a String + + the name of a binding that exists in [[TargetModuleRec]]'s module Environment Record. +
+

The behaviour of the additional concrete specification methods for module Environment Records are defined by the following algorithms:

@@ -11031,14 +11157,15 @@

1. Assert: _S_ is *true*. 1. Assert: _envRec_.HasBinding(_N_) is *true*. - 1. Let _binding_ be the binding for _N_ in _envRec_.[[Bindings]]. - 1. If _binding_ is an indirect binding, then - 1. Let _M_ and _N2_ be the indirection values provided when this binding for _N_ was created. + 1. Let _binding_ be the DeclarativeBindingRecord in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_. + 1. If _binding_ is an ImportDeclarativeBindingRecord, then + 1. Let _M_ be _binding_.[[TargetModuleRec]]. + 1. Let _N2_ be _binding_.[[TargetName]]. 1. Let _targetEnv_ be _M_.[[Environment]]. 1. If _targetEnv_ is ~empty~, throw a *ReferenceError* exception. 1. Return ? _targetEnv_.GetBindingValue(_N2_, *true*). - 1. If _binding_ is an uninitialized binding, throw a *ReferenceError* exception. - 1. Return the value currently bound in _binding_. + 1. If _binding_.[[IsInitialized]] is *false*, throw a *ReferenceError* exception. + 1. Return _binding_.[[BoundValue]].

_S_ will always be *true* because a |Module| is always strict mode code.

@@ -11096,7 +11223,7 @@

1. Assert: _envRec_.HasBinding(_N_) is *false*. 1. Assert: When _M_.[[Environment]] is instantiated it will have a direct binding for _N2_. - 1. Let _binding_ be an immutable indirect binding for _N_ that references _M_ and _N2_ as its target binding and record that the binding is initialized. + 1. Let _binding_ be ImportDeclarativeBindingRecord { [[BoundName]]: _N_, [[IsInitialized]]: *true*, [[BoundValue]]: *undefined*, [[IsMutable]]: *false*, [[IsDeletable]]: *false*, [[IsStrict]]: *false*, [[TargetModuleRec]]: _M_, [[TargetName]]: _N2_ }. 1. Append _binding_ to _envRec_.[[Bindings]]. 1. Return NormalCompletion(~empty~). @@ -47155,8 +47282,8 @@

Changes to BlockDeclarationInstantiation

During BlockDeclarationInstantiation the following steps are performed in place of step :

- 1. Let _binding_ be the binding for _fn_ in _env_.[[Bindings]]. - 1. If _binding_ is an uninitialized binding, then + 1. Let _binding_ be the DeclarativeBindingRecord in _env_.[[Bindings]] whose [[BoundName]] field equals _fn_. + 1. If _binding_.[[IsInitialized]] is *false*, then 1. Perform _env_.InitializeBinding(_fn_, _fo_). 1. Else, 1. Assert: _d_ is a |FunctionDeclaration|.