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Editorial: Model a declarative binding as a Record
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@jmdyck
jmdyck committed Jan 27, 2022
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Showing 1 changed file with 97 additions and 26 deletions.
123 changes: 97 additions & 26 deletions spec.html
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Expand Up @@ -10070,14 +10070,53 @@ <h1>Declarative Environment Records</h1>
[[Bindings]]
</td>
<td>
List of bindings
a List of DeclarativeBindings
</td>
<td>
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]].
</td>
</tr>
</table>
</emu-table>

<p>A <dfn>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>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 @@ -10094,7 +10133,7 @@ <h1>
<dd>It determines if the argument identifier is one of the identifiers bound by the record.</dd>
</dl>
<emu-alg>
1. If _envRec_.[[Bindings]] contains a binding for the name that is the value of _N_, return *true*.
1. If _envRec_.[[Bindings]] contains a DeclarativeBinding whose [[BoundName]] field is equal to the value of _N_, return *true*.
1. Return *false*.
</emu-alg>
</emu-clause>
Expand All @@ -10115,7 +10154,7 @@ <h1>
</dl>
<emu-alg>
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 SimpleDeclarativeBinding { [[BoundName]]: _N_, [[BoundValue]]: ~uninitialized~, [[IsMutable]]: *true*, [[IsDeletable]]: _D_, [[IsStrict]]: *false* }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return NormalCompletion(~empty~).
</emu-alg>
Expand All @@ -10137,7 +10176,7 @@ <h1>
</dl>
<emu-alg>
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 SimpleDeclarativeBinding { [[BoundName]]: _N_, [[BoundValue]]: ~uninitialized~, [[IsMutable]]: *false*, [[IsDeletable]]: *false*, [[IsStrict]]: _S_ }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return NormalCompletion(~empty~).
</emu-alg>
Expand All @@ -10159,10 +10198,10 @@ <h1>
</dl>
<emu-alg>
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. <emu-not-ref>Record</emu-not-ref> that _binding_ has been initialized.
1. Let _binding_ be the DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field equals _N_.
1. Assert: _binding_ is a SimpleDeclarativeBinding.
1. Assert: _binding_.[[BoundValue]] is ~uninitialized~.
1. Set _binding_.[[BoundValue]] to _V_.
1. Return NormalCompletion(~empty~).
</emu-alg>
</emu-clause>
Expand All @@ -10188,10 +10227,12 @@ <h1>
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 DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field equals _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~, 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.
Expand Down Expand Up @@ -10219,9 +10260,10 @@ <h1>
</dl>
<emu-alg>
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 DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field equals _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 @@ -10240,8 +10282,9 @@ <h1>
</dl>
<emu-alg>
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 DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field equals _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>
Expand Down Expand Up @@ -11250,6 +11293,31 @@ <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>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 @@ -11269,14 +11337,16 @@ <h1>
<emu-alg>
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 DeclarativeBinding in _envRec_.[[Bindings]] whose [[BoundName]] field equals _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 _binding_ is an uninitialized binding, throw a *ReferenceError* exception.
1. Return the value currently bound in _binding_.
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 @@ -11334,7 +11404,7 @@ <h1>
<emu-alg>
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 ImportDeclarativeBinding { [[BoundName]]: _N_, [[TargetModuleRec]]: _M_, [[TargetName]]: _N2_ }.
1. Append _binding_ to _envRec_.[[Bindings]].
1. Return NormalCompletion(~empty~).
</emu-alg>
Expand Down Expand Up @@ -47418,8 +47488,9 @@ <h1>Changes to BlockDeclarationInstantiation</h1>
</emu-alg>
<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. Let _binding_ be the binding for _fn_ in _env_.[[Bindings]].
1. If _binding_ is an uninitialized binding, then
1. Let _binding_ be the DeclarativeBinding in _env_.[[Bindings]] whose [[BoundName]] field equals _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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