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initial pass of Tuple group/groupToMap for proposal-array-grouping #317

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initial pass of Tuple group/groupToMap for proposal-array-grouping #317

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66 changes: 66 additions & 0 deletions spec/immutable-data-structures.html
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Expand Up @@ -563,6 +563,72 @@ <h1>Tuple.prototype.with ( _index_, _value_ )</h1>
1. Return a new Tuple value whose [[Sequence]] is _list_.
</emu-alg>
</emu-clause>

<emu-clause id="sec-tuple.prototype.group">
<h1>Tuple.prototype.group ( _callbackfn_ [ , _thisArg_ ] )</h1>
<emu-note>
<p>_callbackfn_ should be a function that accepts three arguments. `group` calls _callbackfn_ once for each element in the Tuple, in ascending order, and constructs a new object of arrays. Each value returned by _callbackfn_ is coerced to a property key, and the associated element is included in the array in the constructed object according to this property key.</p>
<p>If a _thisArg_ parameter is provided, it will be used as the *this* value for each invocation of _callbackfn_. If it is not provided, *undefined* is used instead.</p>
<p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the Tuple being traversed.</p>
<p>The return value of `group` is an object that does not inherit from _Object.prototype_.</p>
</emu-note>
<p>When the `group` method is called with one or two arguments, the following steps are taken:</p>
<emu-alg>
1. Let _O_ be ? ToObject(*this* value).
1. Let _len_ be ? LengthOfArrayLike(_O_).
1. If IsCallable(_callbackfn_) is *false*, throw a *TypeError* exception.
1. Let _k_ be 0.
1. Let _groups_ be a new empty List.
1. Repeat, while _k_ &lt; _len_
1. Let _Pk_ be ! ToString(𝔽(_k_)).
1. Let _kValue_ be ? Get(_O_, _Pk_).
1. Let _propertyKey_ be ? ToPropertyKey(? Call(_callbackfn_, _thisArg_, &laquo; _kValue_, 𝔽(_k_), _O_ &raquo;)).
1. Perform AddValueToKeyedGroup(_groups_, _propertyKey_, _kValue_).
1. Set _k_ to _k_ + 1.
1. Let _obj_ be OrdinaryObjectCreate(*null*).
1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
1. Let _elements_ be CreateArrayFromList(_g_.[[Elements]]).
1. Perform ! CreateDataPropertyOrThrow(_obj_, _g_.[[Key]], _elements_).
1. Return _obj_.
</emu-alg>
<emu-note>
<p>The `group` function is intentionally generic; it does not require that its *this* value be a Tuple object. Therefore it can be transferred to other kinds of objects for use as a method.</p>
</emu-note>
</emu-clause>

<emu-clause id="sec-tuple.prototype.grouptomap">
<h1>Tuple.prototype.groupToMap ( _callbackfn_ [ , _thisArg_ ] )</h1>
<emu-note>
<p>_callbackfn_ should be a function that accepts three arguments. `groupToMap` calls _callbackfn_ once for each element in the Tuple, in ascending order, and constructs a new Map of arrays. Each value returned by _callbackfn_ is used as a key in the Map, and the associated element is included in the array in the constructed Map according to this key.</p>
<p>If a _thisArg_ parameter is provided, it will be used as the *this* value for each invocation of _callbackfn_. If it is not provided, *undefined* is used instead.</p>
<p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the Tuple being traversed.</p>
<p>The return value of `groupToMap` is a Map.</p>
</emu-note>
<p>When the `groupToMap` method is called with one or two arguments, the following steps are taken:</p>
<emu-alg>
1. Let _O_ be ? ToObject(*this* value).
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The other tuple methods we defined with explicit steps all use thisTupleValue(*this* value) instead of ToObject.

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makes sense, I will adjust. I wasn't sure how much to deviate from the original Array versions of these methods.

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Do you think I should instead use the same methodology behind other Array methods like .at and just specify them in terms of the original? Or manually specify the algo here as well.

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manually is probably the better end goal regardless of how you do it in the proposal repo.

1. Let _len_ be ? LengthOfArrayLike(_O_).
1. If IsCallable(_callbackfn_) is *false*, throw a *TypeError* exception.
1. Let _k_ be 0.
1. Let _groups_ be a new empty List.
1. Repeat, while _k_ &lt; _len_
1. Let _Pk_ be ! ToString(𝔽(_k_)).
1. Let _kValue_ be ? Get(_O_, _Pk_).
1. Let _key_ be ? Call(_callbackfn_, _thisArg_, &laquo; _kValue_, 𝔽(_k_), _O_ &raquo;).
1. If _key_ is *-0*<sub>𝔽</sub>, set _key_ to *+0*<sub>𝔽</sub>.
1. Perform AddValueToKeyedGroup(_groups_, _key_, _kValue_).
1. Set _k_ to _k_ + 1.
1. Let _map_ be ! Construct(%Map%).
1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
1. Let _elements_ be CreateArrayFromList(_g_.[[Elements]]).
1. Let _entry_ be the Record { [[Key]]: _g_.[[Key]], [[Value]]: _elements_ }.
1. Append _entry_ as the last element of _map_.[[MapData]].
1. Return _map_.
</emu-alg>
<emu-note>
<p>The `groupToMap` function is intentionally generic; it does not require that its *this* value be a Tuple object. Therefore it can be transferred to other kinds of objects for use as a method.</p>
</emu-note>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>