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Editorial: Model the bindings of a declarative Env Rec as a List of Records #2288

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Editorial: Model the bindings of a declarative Env Rec as a List of Records #2288

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346aafe
Editorial: Use Declarative Env Rec's HasBinding method
jmdyck Jan 24, 2021
4af342b
Editorial: Treat a binding as an 'alias-able' thing
jmdyck Jan 24, 2021
5cb0725
Editorial: Declarative Env Rec has field [[Bindings]]
jmdyck Jan 24, 2021
126c62c
Editorial: Model a declarative binding as a Record
jmdyck Jan 24, 2021
ade059f
fixup: add 'variants' attributes; change "equals" to "is"
jmdyck Sep 3, 2023
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169 changes: 140 additions & 29 deletions spec.html
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Expand Up @@ -10199,6 +10199,72 @@ <h1>The Environment Record Type Hierarchy</h1>
<emu-clause id="sec-declarative-environment-records">
<h1>Declarative Environment Records</h1>
<p>Each <dfn variants="Declarative Environment Records">Declarative Environment Record</dfn> is associated with an ECMAScript program scope containing variable, constant, let, class, module, import, and/or function declarations. A Declarative Environment Record binds the set of identifiers defined by the declarations contained within its scope.</p>
<p>Declarative Environment Records have the additional fields listed in <emu-xref href="#table-additional-fields-of-declarative-environment-records"></emu-xref>.</p>
<emu-table id="table-additional-fields-of-declarative-environment-records" caption="Additional Fields of Declarative Environment Records">
<table>
<tr>
<th>
Field Name
</th>
<th>
Value
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[Bindings]]
</td>
<td>
a List of DeclarativeBindings
</td>
<td>
Satisfies the invariant that no two records in [[Bindings]] have the same [[BoundName]].
</td>
</tr>
</table>
</emu-table>

<p>A <dfn variants="DeclarativeBindings">DeclarativeBinding</dfn> is either a SimpleDeclarativeBinding or an ImportDeclarativeBinding. SimpleDeclarativeBindings can appear in any Declarative Environment Record, but ImportDeclarativeBindings can only appear in a Module Environment Record.</p>

<p>A <dfn variants="SimpleDeclarativeBindings">SimpleDeclarativeBinding</dfn> has the following fields:</p>
<emu-table id="table-fields-of-simpledeclarativebindings" caption="SimpleDeclarativeBinding Fields">
<table>
<tr>
<th>Field Name</th>
<th>Value</th>
<th>Meaning</th>
</tr>
<tr>
<td>[[BoundName]]</td>
<td>a String</td>
<td>the name being bound.</td>
</tr>
<tr>
<td>[[BoundValue]]</td>
<td>an ECMAScript language value or ~uninitialized~</td>
<td>the value that the name is bound to.</td>
</tr>
<tr>
<td>[[IsMutable]]</td>
<td>a Boolean</td>
<td>if *true*, indicates that the binding is mutable.</td>
</tr>
<tr>
<td>[[IsDeletable]]</td>
<td>a Boolean</td>
<td>if *true*, indicates that the binding may be deleted by a subsequent DeleteBinding call.</td>
</tr>
<tr>
<td>[[IsStrict]]</td>
<td>a Boolean</td>
<td>if *true*, indicates that the binding is a strict binding.</td>
</tr>
</table>
</emu-table>

<p>The behaviour of the concrete specification methods for Declarative Environment Records is defined by the following algorithms.</p>

<emu-clause id="sec-declarative-environment-records-hasbinding-n" type="concrete method">
Expand All @@ -10215,7 +10281,7 @@ <h1>
<dd>It determines if the argument identifier is one of the identifiers bound by the record.</dd>
</dl>
<emu-alg>
1. If _envRec_ has a binding for _N_, return *true*.
1. If _envRec_.[[Bindings]] contains a DeclarativeBinding whose [[BoundName]] field is _N_, return *true*.
1. Return *false*.
</emu-alg>
</emu-clause>
Expand All @@ -10235,8 +10301,9 @@ <h1>
<dd>It creates a new mutable binding for the name _N_ that is uninitialized. A binding must not already exist in this Environment Record for _N_. If _D_ is *true*, the new binding is marked as being subject to deletion.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ does not already have a binding for _N_.
1. Create a mutable binding in _envRec_ 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. Assert: _envRec_.HasBinding(_N_) is *false*.
1. Let _binding_ be SimpleDeclarativeBinding { [[BoundName]]: _N_, [[BoundValue]]: ~uninitialized~, [[IsMutable]]: *true*, [[IsDeletable]]: _D_, [[IsStrict]]: *false* }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return ~unused~.
</emu-alg>
</emu-clause>
Expand All @@ -10256,8 +10323,9 @@ <h1>
<dd>It creates a new immutable binding for the name _N_ that is uninitialized. A binding must not already exist in this Environment Record for _N_. If _S_ is *true*, the new binding is marked as a strict binding.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ does not already have a binding for _N_.
1. Create an immutable binding in _envRec_ for _N_ and record that it is uninitialized. If _S_ is *true*, record that the newly created binding is a strict binding.
1. Assert: _envRec_.HasBinding(_N_) is *false*.
1. Let _binding_ be SimpleDeclarativeBinding { [[BoundName]]: _N_, [[BoundValue]]: ~uninitialized~, [[IsMutable]]: *false*, [[IsDeletable]]: *false*, [[IsStrict]]: _S_ }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return ~unused~.
</emu-alg>
</emu-clause>
Expand All @@ -10277,9 +10345,11 @@ <h1>
<dd>It is used to set the bound value of the current binding of the identifier whose name is _N_ to the value _V_. An uninitialized binding for _N_ must already exist.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ must have an uninitialized binding for _N_.
1. Set the bound value for _N_ in _envRec_ to _V_.
1. <emu-not-ref>Record</emu-not-ref> that the binding for _N_ in _envRec_ has been initialized.
1. Assert: _envRec_.HasBinding(_N_) is *true*.
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field is _N_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. Assert: _binding_.[[BoundValue]] is ~uninitialized~.
1. Set _binding_.[[BoundValue]] to _V_.
1. Return ~unused~.
</emu-alg>
</emu-clause>
Expand All @@ -10300,15 +10370,18 @@ <h1>
<dd>It attempts to change the bound value of the current binding of the identifier whose name is _N_ to the value _V_. A binding for _N_ normally already exists, but in rare cases it may not. If the binding is an immutable binding, a *TypeError* is thrown if _S_ is *true*.</dd>
</dl>
<emu-alg>
1. [id="step-setmutablebinding-missing-binding"] If _envRec_ does not have a binding for _N_, then
1. [id="step-setmutablebinding-missing-binding"] If _envRec_.HasBinding(_N_) is *false*, then
1. If _S_ is *true*, throw a *ReferenceError* exception.
1. Perform ! _envRec_.CreateMutableBinding(_N_, *true*).
1. Perform ! _envRec_.InitializeBinding(_N_, _V_).
1. Return ~unused~.
1. If the binding for _N_ in _envRec_ is a strict binding, set _S_ to *true*.
1. If the binding for _N_ in _envRec_ has not yet been initialized, then
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field is _N_.
1. If _binding_ is an ImportDeclarativeBinding, throw a *TypeError* exception.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. If _binding_.[[IsStrict]] is *true*, set _S_ to *true*.
1. If _binding_.[[BoundValue]] is ~uninitialized~, then
1. Throw a *ReferenceError* exception.
1. Else if the binding for _N_ in _envRec_ is a mutable binding, then
1. Else if _binding_.[[IsMutable]] is *true*, then
1. Change its bound value to _V_.
1. Else,
1. Assert: This is an attempt to change the value of an immutable binding.
Expand Down Expand Up @@ -10336,9 +10409,11 @@ <h1>
<dd>It returns the value of its bound identifier whose name is _N_. If the binding exists but is uninitialized a *ReferenceError* is thrown, regardless of the value of _S_.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ has a binding for _N_.
1. If the binding for _N_ in _envRec_ is an uninitialized binding, throw a *ReferenceError* exception.
1. Return the value currently bound to _N_ in _envRec_.
1. Assert: _envRec_.HasBinding(_N_) is *true*.
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field is _N_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. If _binding_.[[BoundValue]] is ~uninitialized~, throw a *ReferenceError* exception.
1. Return _binding_.[[BoundValue]].
</emu-alg>
</emu-clause>

Expand All @@ -10356,9 +10431,11 @@ <h1>
<dd>It can only delete bindings that have been explicitly designated as being subject to deletion.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ has a binding for _N_.
1. If the binding for _N_ in _envRec_ cannot be deleted, return *false*.
1. Remove the binding for _N_ from _envRec_.
1. Assert: _envRec_.HasBinding(_N_) is *true*.
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field is _N_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. If _binding_.[[IsDeletable]] is *false*, return *false*.
1. Remove _binding_ from _envRec_.[[Bindings]].
1. Return *true*.
</emu-alg>
</emu-clause>
Expand Down Expand Up @@ -11378,6 +11455,31 @@ <h1>Module Environment Records</h1>
</tr>
</table>
</emu-table>
<p>The [[Bindings]] of a Module Environment Record can include both SimpleDeclarativeBindings and ImportDeclarativeBindings. An <dfn variants="ImportDeclarativeBindings">ImportDeclarativeBinding</dfn> has the following fields:</p>
<emu-table id="table-fields-of-importdeclarativebindings" caption="ImportDeclarativeBinding Fields">
<table>
<tr>
<th>Field Name</th>
<th>Value</th>
<th>Meaning</th>
</tr>
<tr>
<td>[[BoundName]]</td>
<td>a String</td>
<td>the name being bound.</td>
</tr>
<tr>
<td>[[TargetModuleRec]]</td>
<td>a Module Record</td>
<td>the imported module that provides the binding.</td>
</tr>
<tr>
<td>[[TargetName]]</td>
<td>a String</td>
<td>the name of a binding that exists in the target module.</td>
</tr>
</table>
</emu-table>
<p>The behaviour of the additional concrete specification methods for Module Environment Records are defined by the following algorithms:</p>

<emu-clause id="sec-module-environment-records-getbindingvalue-n-s" type="concrete method">
Expand All @@ -11396,14 +11498,17 @@ <h1>
</dl>
<emu-alg>
1. Assert: _S_ is *true*.
1. Assert: _envRec_ has a binding for _N_.
1. If the binding for _N_ is an indirect binding, then
1. Let _M_ and _N2_ be the indirection values provided when this binding for _N_ was created.
1. Assert: _envRec_.HasBinding(_N_) is *true*.
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field is _N_.
1. If _binding_ is an ImportDeclarativeBinding, 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 ? <emu-meta effects="user-code">_targetEnv_.GetBindingValue</emu-meta>(_N2_, *true*).
1. If the binding for _N_ in _envRec_ is an uninitialized binding, throw a *ReferenceError* exception.
1. Return the value currently bound to _N_ in _envRec_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. If _binding_.[[BoundValue]] is ~uninitialized~, throw a *ReferenceError* exception.
1. Return _binding_.[[BoundValue]].
</emu-alg>
<emu-note>
<p>_S_ will always be *true* because a |Module| is always strict mode code.</p>
Expand Down Expand Up @@ -11459,9 +11564,10 @@ <h1>
<dd>It creates a new initialized immutable indirect binding for the name _N_. A binding must not already exist in this Environment Record for _N_. _N2_ is the name of a binding that exists in _M_'s Module Environment Record. Accesses to the value of the new binding will indirectly access the bound value of the target binding.</dd>
</dl>
<emu-alg>
1. Assert: _envRec_ does not already have a binding for _N_.
1. Assert: _envRec_.HasBinding(_N_) is *false*.
1. Assert: When _M_.[[Environment]] is instantiated, it will have a direct binding for _N2_.
1. Create an immutable indirect binding in _envRec_ for _N_ that references _M_ and _N2_ as its target binding and record that the binding is initialized.
1. Let _binding_ be ImportDeclarativeBinding { [[BoundName]]: _N_, [[TargetModuleRec]]: _M_, [[TargetName]]: _N2_ }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return ~unused~.
</emu-alg>
</emu-clause>
Expand Down Expand Up @@ -11503,7 +11609,8 @@ <h1>
<dl class="header">
</dl>
<emu-alg>
1. Let _env_ be a new Declarative Environment Record containing no bindings.
1. Let _env_ be a new Declarative Environment Record.
1. Set _env_.[[Bindings]] to « ».
1. Set _env_.[[OuterEnv]] to _E_.
1. Return _env_.
</emu-alg>
Expand Down Expand Up @@ -11538,7 +11645,8 @@ <h1>
<dl class="header">
</dl>
<emu-alg>
1. Let _env_ be a new Function Environment Record containing no bindings.
1. Let _env_ be a new Function Environment Record.
1. Set _env_.[[Bindings]] to « ».
1. Set _env_.[[FunctionObject]] to _F_.
1. If _F_.[[ThisMode]] is ~lexical~, set _env_.[[ThisBindingStatus]] to ~lexical~.
1. Else, set _env_.[[ThisBindingStatus]] to ~uninitialized~.
Expand Down Expand Up @@ -11579,7 +11687,8 @@ <h1>
<dl class="header">
</dl>
<emu-alg>
1. Let _env_ be a new Module Environment Record containing no bindings.
1. Let _env_ be a new Module Environment Record.
1. Set _env_.[[Bindings]] to « ».
1. Set _env_.[[OuterEnv]] to _E_.
1. Return _env_.
</emu-alg>
Expand Down Expand Up @@ -51766,7 +51875,9 @@ <h1>Changes to BlockDeclarationInstantiation</h1>
<p>During BlockDeclarationInstantiation the following steps are performed in place of step <emu-xref href="#step-blockdeclarationinstantiation-initializebinding"></emu-xref>:</p>
<emu-alg replaces-step="step-blockdeclarationinstantiation-initializebinding">
1. Perform the following steps:
1. If the binding for _fn_ in _env_ is an uninitialized binding, then
1. Let _binding_ be the DeclarativeBinding in _env_.[[Bindings]] whose [[BoundName]] field is _fn_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. If _binding_.[[BoundValue]] is ~uninitialized~, then
1. Perform ! _env_.InitializeBinding(_fn_, _fo_).
1. Else,
1. Assert: _d_ is a |FunctionDeclaration|.
Expand Down
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