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66 changes: 36 additions & 30 deletions misc/oxcaml/oxcaml-basics/slides/index.html
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Expand Up @@ -944,13 +944,13 @@ <h1>Value layouts and unboxing</h1>
</section>

<section class="slide concept-slide">
<h2>Runtime invariant: one OCaml value word</h2>
<h2>Runtime invariant: every OCaml value is one word</h2>
<div class="value-model-figure">
<div class="value-model-grid">
<div class="value-model-panel">
<h3>Immediate value</h3>
<div class="value-word value-word-immediate"><span class="value-word-main">63 bits of immediate data</span><span class="value-word-tag">1</span></div>
<p>Small integers and constructors with no payload use this shape.</p>
<p><code>int</code>, <code>char</code>, <code>bool</code>, <code>unit</code>, etc. use this shape.</p>
</div>
<div class="value-model-panel">
<h3>Pointer value</h3>
Expand All @@ -965,7 +965,7 @@ <h3>Pointer value</h3>
<div class="heap-model-word"><strong>payload N</strong><span>value or raw data</span></div>
</div>
</div>
<p>The word points to a heap block with a header and payload words.</p>
<p>Records, tuples, arrays, etc. use this shape.</p>
</div>
</div>
</div>
Expand All @@ -983,59 +983,61 @@ <h2>Heap block anatomy</h2>
<div class="heap-model-word"><strong>payload N</strong><span>value or raw data</span></div>
</div>
</div>
<p class="takeaway">The GC follows fields described as values. Raw data fields are not scanned as pointers.</p>
<p class="takeaway">The header describes which fields are values vs. raw data. The GC does not scan raw data.</p>
<aside class="notes">This distinction matters for unboxed float fields and mixed blocks.</aside>
</section>

<section class="slide concept-slide">
<h2>Uniform value representation is powerful</h2>
<div class="two-up">
<article><h3>Source</h3><pre><code>let plain_value_integer = 5

let plain_value_tuple = (1, 2, 3)

type quote =
{ symbol : string
; price : int
; mutable size : int
}</code></pre></article>
<article><h3>Runtime model</h3><p>GC, polymorphism, tuples, records, variants, and libraries all agree on one value shape.</p></article>
<article><h3>Runtime model</h3><p>The runtime, GC, and libraries all agree on one value shape. Polymorphic functions are only compiled once.</p></article>
</div>
<aside class="notes">The uniform model is a strength before it is a cost.</aside>
</section>

<section class="slide concept-slide">
<h2>Variants and recursive data are values too</h2>
<h2>Variants are values too</h2>
<div class="two-up">
<article><h3>Constant constructors</h3><p>Represented as immediates.</p></article>
<article><h3>Payload constructors</h3><p>Allocate heap blocks; the header tag identifies the constructor.</p></article>
</div>
<p class="takeaway">Recursive data is a graph of value words and heap blocks.</p>
<p class="takeaway">Recursive data is a graph of values: immediates or pointers to other heap blocks.</p>
<aside class="notes">This is where the representation visualizer is strongest in the course page.</aside>
</section>

<section class="slide concept-slide">
<h2>Sharing: the heap is a graph</h2>
<pre><code>let shared = "shared"
let t = (shared, shared, "other")</code></pre>
<p class="takeaway">Two fields can point at the same heap object. Visualizations must preserve sharing.</p>
<p class="takeaway">Two fields can point at the same heap object.</p>
<aside class="notes">Do not redraw shared heap graphs as trees.</aside>
</section>

<section class="slide concept-slide">
<h2>Uniform model costs: boxes and pointers</h2>
<div class="cost-ledger">
<article><h3>boxed numeric values</h3><pre><code>let boxed_numeric_values =
(3.5, 456L)</code></pre><p>tuple block, boxed float, boxed int64</p></article>
(3.5, 456L)</code></pre><p>tuple block, boxed <code>float</code>, boxed <code>int64</code></p></article>
<article><h3>ordinary option values</h3><pre><code>let ordinary_option_values =
(None, Some "found")</code></pre><p>Some wrapper block</p></article>
(None, Some "found")</code></pre><p><code>Some</code> constructor requires a block</p></article>
</div>
<aside class="notes">Boxes mean allocation, headers, pointer indirection, and future GC work.</aside>
</section>

<section class="slide concept-slide">
<h2>Layouts remove specific boxes</h2>
<h2>Unboxed types remove specific boxes</h2>
<div class="cost-ledger">
<article><h3>ordinary tuple</h3><pre><code>(1, "one")</code></pre><p>one heap block for grouping</p></article>
<article class="ok-card"><h3>unboxed product</h3><pre><code>#(1, "one")</code></pre><p>tuple block removed; string heap object remains</p></article>
<article class="ok-card"><h3>unboxed tuple</h3><pre><code>#(1, "one")</code></pre><p>tuple block removed; string heap object remains</p></article>
</div>
<aside class="notes">Unboxing removes the specified box, not everything reachable.</aside>
</section>
Expand All @@ -1062,7 +1064,7 @@ <h2>Unboxed records inline nested fields</h2>
</section>

<section class="slide live-slide">
<h2>or_null removes option wrapper allocation</h2>
<h2><code>or_null</code> removes option wrapper allocation</h2>
<div class="live-layout">
<div class="live-copy">
<div class="repr-map">
Expand Down Expand Up @@ -1096,10 +1098,11 @@ <h2>or_null removes option wrapper allocation</h2>
</section>

<section class="slide live-slide">
<h2>or_null answer</h2>
<h2><code>or_null</code> answer</h2>
<div class="live-layout">
<div class="live-copy">
<p><code>Null</code> replaces <code>None</code>.</p>
<br>
<p><code>This x</code> replaces <code>Some x</code> without adding a wrapper block around <code>x</code>.</p>
</div>
<div class="live-editor-frame" tabindex="-1">
Expand All @@ -1119,11 +1122,13 @@ <h2>or_null answer</h2>
</section>

<section class="slide live-slide or-null-error-slide">
<h2>The limit: or_null cannot be nested</h2>
<h2>The limit: <code>or_null</code> cannot be nested</h2>
<div class="live-layout">
<div class="live-copy">
<p><code>Null</code> is represented by the null machine word.</p>
<br>
<p>If <code>string or_null or_null</code> were allowed, the same null word would need two meanings: the outer missing value and the inner missing value.</p>
<br>
<p class="diagnostic-callout">The payload of <code>or_null</code> must be non-null. A value that is already <code>or_null</code> is maybe-null.</p>
</div>
<div class="live-editor-frame" tabindex="-1">
Expand All @@ -1141,6 +1146,7 @@ <h2>Kinds record allowed representations</h2>
<div class="live-layout">
<div class="live-copy">
<p>If an error says a type parameter expects <code>value</code>, the API expects ordinary one-word OCaml values.</p>
<br>
<p>Edit the kind bound from <code>value</code> to <code>float64</code>.</p>
</div>
<div class="live-editor-frame" tabindex="-1">
Expand Down Expand Up @@ -1172,18 +1178,18 @@ <h2>Abstract types need public kinds</h2>
<section class="slide concept-slide">
<h2>Polymorphic code still has a layout</h2>
<div class="two-up">
<article><h3>ordinary map</h3><pre><code>let rec map_value
: ('a : value) ('b : value).
('a -> 'b)
-> 'a list
-> 'b list</code></pre></article>
<article><h3>ordinary map</h3><pre><code>val map_value
: ('a : value) ('b : value)
. ('a -> 'b)
-> 'a list
-> 'b list</code></pre></article>
<article><h3>product layout map</h3><pre><code>type ('a : value & value) product_list = ...

let rec map_product_list
: ('a : value & value) ('b : value & value).
('a -> 'b)
-> 'a product_list
-> 'b product_list</code></pre></article>
val map_product_list
: ('a : value & value) ('b : value & value)
. ('a -> 'b)
-> 'a product_list
-> 'b product_list</code></pre></article>
</div>
<aside class="notes">Code must know how many components are passed, returned, stored, and scanned.</aside>
</section>
Expand All @@ -1193,16 +1199,16 @@ <h2>Templates reduce layout-specific repetition</h2>
<pre><code>let%template[@kind k = (value, value & value)] id
: ('a : k). 'a -> 'a =
fun x -> x</code></pre>
<p class="takeaway">One source pattern can generate related checked definitions with different calling conventions.</p>
<p class="takeaway">One source pattern can generate multiple definitions with different calling conventions.</p>
<aside class="notes">Keep this as recognition material, not a deep ppx_template lesson.</aside>
</section>

<section class="slide summary-slide">
<h2>Choose the checked lever</h2>
<h2>Choose the correct lever</h2>
<div class="lever-grid">
<article><h3>Race risk</h3><p>Use contention and portability requirements.</p></article>
<article><h3>Lifetime or heap allocation risk</h3><p>Use local, stack_, and exclave_.</p></article>
<article><h3>Box or pointer cost</h3><p>Use layouts, unboxed values, or_null, kinds, and templates.</p></article>
<article><h3>Data race safety</h3><p>Use contention and portability requirements.</p></article>
<article><h3>Lifetime correctness or heap allocation cost</h3><p>Use <code>local</code>, <code>stack_</code>, and <code>exclave_</code>.</p></article>
<article><h3>Box or pointer cost</h3><p>Use layouts, unboxed types, and <code>or_null</code>.</p></article>
</div>
<p class="takeaway">All three make performance-sensitive intent explicit and checked.</p>
<aside class="notes">This is the final durable takeaway.</aside>
Expand Down