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el/docs/architecture/capabilities.md
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bigmerge 15d4352bac make the capability table match its own status note
The note said serialization, text encoding, storage, network, concurrency and
emission had collapsed; the table still listed all six as live capabilities.
A document that contradicts itself one screen apart is worse than one that is
merely out of date.

Also renames 27 from Secrecy to Concealment. 'Secrecy' covered one of the three
things in that row and got the other two backwards: a hash is public and a
signature exists to be read. Integrity and authenticity are grounding under
adversarial conditions, which is row 16. Only concealment stands alone.
2026-08-17 09:37:35 -05:00

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# El — Capabilities
**What the language can do, stated as capabilities rather than as code.**
This list is the unit of analysis. Each entry gets one question — *prove this
cannot be done with pure geometry* — and the answer determines whether it stays a
capability of the language or collapses into the manifold.
Draft, 2026-08-17. Ordered roughly from most-likely-geometry to most-likely-code.
**Status after measurement.** The list was audited against the implementation
the same day. 28 entries collapsed to 19 geometry + 3 code: serialization, text
encoding, network and emission are all *projection onto a basis* (row 18) —
the convention is the basis, never the act. Storage collapsed because
persistence has no caller. Concurrency collapsed because coordination is the
price of forgetting, not a capability. A fourth proof form was added,
**adversarial exactness**, and form 1 stopped being a valid verdict.
**The table answers CAN only.** SHOULD and COST resolve per *site*, not per
capability — `is_digit` and `is_letter` are one capability with opposite
answers, and comparison spans three cost tiers. See the notes below.
---
## The list
| # | Capability | What it means | Verdict |
|---|---|---|---|
| 1 | **Comparison** | is this the same as that; is this greater | zero distance / sign of a displacement |
| 2 | **Ordering** | arrange by a criterion | position along an axis |
| 3 | **Containment** | is this inside that; does this contain that | region membership |
| 4 | **Correspondence** | where does this occur in that; how much of this is in that | a match-strength field over a span |
| 5 | **Segmentation** | divide a whole into parts | boundaries at measured discontinuity |
| 6 | **Composition** | join parts into a whole | adjacency; one position with parts |
| 7 | **Classification** | what kind of thing is this | which region does it land in |
| 8 | **Naming / binding** | attach a name to a thing and find it again | an edge; retrieval is projection |
| 9 | **Collection** | many things held together, indexed, counted | a set of positions; cardinality; projection onto the i-th |
| 10 | **Iteration** | do something for each of many | traversal |
| 11 | **Arithmetic** | quantity, magnitude, combination | displacement algebra on a line |
| 12 | **Time** | when; how long; how often | a 1-D affine space — instants are points, durations displacements, rhythms phases on a circle |
| 13 | **Identity** | which one is this; are these two the same one | coincidence of position |
| 14 | **Selection / dispatch** | choose which behaviour applies | nearest region |
| 15 | **Transformation** | produce a thing from a thing | change of basis |
| 16 | **Grounding** | how well is this supported | the weight on an edge. Has no caller |
| 17 | **Learning** | get better at something | standing changing over time |
| 18 | **Projection** | render meaning onto a surface | change of basis onto a surface basis |
| 19 | **Transduction** | take a signal in | change of basis from a sensor basis |
| ~~20~~ | ~~Serialization~~ | **collapsed → 18.** The format is a basis; projecting onto it is the act | — |
| ~~21~~ | ~~Text encoding~~ | **collapsed → 18.** An encoding is a basis | — |
| ~~22~~ | ~~Storage~~ | **collapsed.** No save — persistence has no caller. Durability survives at one site inside the engram | — |
| ~~23~~ | ~~Network~~ | **split.** Wire format → 18; socket → 24 | — |
| 24 | **Process / OS** | syscalls; the one-way boundary. Where monotonicity stops | CODE, form 2 |
| ~~25~~ | ~~Concurrency~~ | **collapsed.** Monotone state needs no coordination; coordination is the price of forgetting | — |
| 26 | **Memory substrate** | what holds the positions | CODE, form 3 |
| 27 | **Concealment** | meaning made unreadable without a key. *Renamed*: "secrecy" covered one of three things and got the other two backwards — a hash is public, a signature exists to be read. Integrity and authenticity are **grounding under adversarial conditions** (row 16); only concealment stands alone | CODE, form 4 |
| ~~28~~ | ~~Emission~~ | **split.** Laying out → 18; the device write → 24 | — |
---
## Notes on the boundary cases
**27 — Secrecy is the one capability geometry cannot hold, and the proof is not
form 1.** A cryptographic hash is a *deliberately structure-destroying* map: its
entire value is that near inputs land at maximally uncorrelated outputs. Geometry
is the claim that near things stay near. A manifold that approximated SHA-256
would *be* a break of SHA-256. Signature verification is the same: 0.99-valid is
invalid. And X25519 *is* geometry — a group on an elliptic curve — which is
precisely why it must be code, because its security is the *hardness of moving in
that geometry*.
This is a fourth proof form and it should be added to `geometry-vs-code.md`:
**adversarial exactness.** Where approximation is a break, geometry is excluded.
**20, 21 — Serialization and text encoding are convention all the way down**, but
only at the *edge*. The byte format is agreed; what is being written is not. Do not
let a geometric computation inherit a code verdict because its result gets
serialized.
**11, 12 — Arithmetic and time are the same capability.** Instants are points,
durations are displacements, pointpoint→vector, point+vector→point. The runtime
already implements this correctly as `el_instant_add_dur` / `el_duration_add`. That
it *also* implements a five-entry string→multiplier table beside it (`time_add`
with `"ms"/"sec"/"min"/"hour"/"day"`) is the residue.
**7 — Classification is the most-violated capability in the codebase.** Seven ASCII
range tables (`is_letter`, `is_digit`, `is_alphanumeric`, `is_whitespace`,
`is_punctuation`, `is_uppercase`, `is_lowercase`) that return false for every
non-ASCII byte. `str_count_letters` reports zero letters for `é`. The wrongness on
most of Unicode is the tell that a table is standing in for a region.
**4 — Correspondence appears five times.** `str_index_of`, `str_index_of_all`,
`str_last_index_of`, `str_count`, `str_find_chars` are five projections of one
match-strength field: first zero, all zeros, last zero, count of zeros, first
class-crossing. One relation, five functions.
**14 — Selection is the crux for the compiler.** `+` dispatching on AST node kind
is selection-by-enumeration where selection-by-position belongs.
**Correction, 2026-08-17, from measurement.** This entry previously also cited
`==` lowering to `str_eq` "unless both operand names are in a hardcoded int-name
set — a literal list of variable names treated as integers." That is **wrong**.
`__int_names` is populated from *type annotations* (`param["type"] == "Int"`,
`let x: Int`), which is primitive but legitimate type propagation, not an
enumeration of blessed variable names.
The real defect was one layer down: `is_int_call` held **35 hardcoded builtin
return types**, the same shape as the 19 temporal ones. Those moved to
`lang/tools/check/signatures.rel`.
And the mischaracterisation hid a live bug. Because the return types were never
consulted at a *binding* site, an unannotated `let` lost its type:
```el
let a = str_len("hello") // no annotation
let b = str_len("hi")
let c = a + b // el_str_concat(a, b) on two integers
```
That compiled clean, ran, and printed nothing where it should print 7 — no error
at any layer. Present in the pre-change compiler, so pre-existing. Fixed by
taking an unannotated `let`'s type from what its initialiser returns; the data
was already required for dispatch and simply never read there.
**The general lesson, since it recurred all session:** the enumeration was real
but I had located it in the wrong place. Naming a defect from reading is a
hypothesis. Eight hours of reading this file did not surface the miscompilation;
moving the data out and running the result did.
---
## What this list is for
Each capability gets audited **once**, across every place it appears — not once per
file. The output is not a percentage. It is:
- which capabilities survive the question and stay in the language
- which collapse into the manifold
- and for each one that collapses, **every site it currently appears at**, because
those sites are the residue and they are what gets deleted.
The line-count audit produced a map of where the residue sits. This produces a map
of **what it is**.