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This page records the design, provenance, and behavioural divergences of [[Module:Auphen]] — out-of-frame notes, kept off the module source.

== Provenance ==

Auphen is a pure-Lua (Scribunto) port of a JavaScript sound-change engine, itself an implementation of ConWorkShop's '''PhoMo''' rule notation. Rule anatomy (target / change / environment / exception / else), the affix-vs-replace split, category sets, and the operator set follow PhoMo; the divergences below are deliberate. The engine is developed and tested off-wiki: a 334-case local suite covering every operation, ground-truth parity against the original JS engine, and the live YBS-PJ ruleset.

== Divergences ==

Fixed bugs in the source JS engine (each has a proving test off-wiki):
* '''D1''' — the ELS <code>@</code>-index is parsed and used as a fallback instance filter (the JS assigned it to the CHG index, so ELS indices were dead).
* '''D2''' — ditto <code>"</code> fires inside the exception as well as the environment (the JS dropped the "previous" flag).
* '''D3''' — <code>?</code>-reversal indices are computed on the clean word; negatives are not off by one, and positive <code>?n</code> starts at char ''n''.
* '''D4''' — positive-index affix insertion/deletion is not off by one.
* '''D5''' — circumfix <code>A#B</code> wraps the word (the JS concatenated A+B).
* '''D6''' — local conditions inside an affix rule are cleanly false.
* '''D14''' — category→category mapping pairs members by '''declaration order''', not a longest-first sort, so digraph categories map correctly (e.g. palatalization <code>[H]/[J]</code> where <code>[J]</code> holds <code>tʃ, dʒ</code>: declared order gives s→ʃ, t→tʃ, g→ɣ). The JS sorted members longest-first, silently mapping s→tʃ. Longest-first is still used for ''matching'', so multi-character phones still match greedily.
* '''D15''' — <code>%</code> ("same as the target") substitutes on '''every''' occurrence in a result, so <code>%%</code> doubles the target (e.g. gemination <code>[C]/%%/_4</code>). The JS replaced only the first <code>%</code>. A literal per-cent sign in output is written <code>!%</code>.
* '''D16''' (Auphen addition) — <code>~</code> (tilde) is a '''universal word boundary'''. The engine splits input on it, so each part is processed as its own word (its own <code>#</code> edges), and the parts are joined with a space; a <code>~</code> produced late by a rule becomes a plain display space. It does not clash with nasal vowels (precomposed like <code>ã</code>, or a combining U+0303 tilde — both distinct codepoints from ASCII <code>~</code>).

Divergences from CWS (documented quirks fixed, not reproduced):
* '''D7''' — a category/index resolving out of range skips the candidate (CWS deletes the target).
* '''D8''' — <code>!</code> escape makes the next character a literal.
* '''D9 / D10''' — movement <code>&gt;</code> and copy <code>&gt;!</code> use clean semantics; CWS's off-by-one is not reproduced.
* '''D11''' — <code>-</code> word operations are opt-in (<code>opts.dashToSpace</code>).
* '''D12''' — the wildcard <code>*</code> in local conditions is defined and reliable.
* '''D13''' — a UTF-8 codepoint layer replaces the JS's UTF-16 indexing: combining marks are separate characters, and digraph phones work in categories (CWS bans them).

Kept behaviours: <code>@0</code>/<code>@-0</code> select nothing; an empty ELS is skip, not delete; capitals never survive to output; candidates are collected against the pre-rule word and applied together (no intra-rule bleeding).

== Performance ==

Category matching currently materialises the Cartesian product of the category references in a rule, so cost is (category size) to the power of (number of references) — dominated by large sets like <code>[C]</code>. A guard (<code>opts.explodeCap</code>, default 5,000,000) skips a pathological rule with a warning rather than exceeding Scribunto's CPU limit. '''Tracked follow-up:''' a streaming/positional matcher that tests membership per word-position, removing the ceiling entirely.
== Crash on left-contexts that run past the start of the word ==

Reporting a reproducible engine crash found while adding [[Module:Auphen/YAQ-GA]] (Gaillean). The data page is correct — it reproduces the operator's CWS ruleset exactly on every word the engine survives — but six of fourteen test words return <code>Lua error: Internal error: The interpreter exited with status 1</code> rather than a wrong answer.

'''Trigger.''' The Gaillean ruleset contains

 ɛ/ə/[V]_[C]|[C]_[C][C][V]|[V][C]_[C][C]|[C][C]_#|ʎ_#|ʒ_#|c_#|g͡ɣ_#/qu_

Every word whose form still contains <code>ɛ</code> when this rule is reached crashes; every word without one is fine. The correlation was exact across twenty probes.

{| class="wikitable"
! input !! result
|-
| <code>e</code>, <code>be</code>, <code>eb</code>, <code>abe</code>, <code>herce</code>, <code>qube</code> || crash
|-
| <code>ea</code>, <code>ab</code>, <code>ka</code>, <code>ghalla</code>, <code>thaembuz</code>, <code>mporonat</code> || correct output
|}

<code>ea</code> is the diagnostic case: it survives only because the preceding rule <code>ɛ/e/_[V]#</code> fires first and removes the <code>ɛ</code>, so the rule above never evaluates.

'''Diagnosis.''' The failing conditions (<code>[V]_[C]</code>, <code>[C][C]_#</code>, …) all have left-hand context. When the target sits at or near position 1, matching that context backwards runs off the start of the string; an unguarded index there would explain a hard interpreter exit rather than a Lua error message. Single-segment probes (<code>qa</code>, <code>xa</code>, <code>ca</code>, <code>anna</code>, <code>atta</code>) all pass, so no individual glyph, category or geminate is implicated.

'''Meanwhile.''' Gaillean entries carry static IPA, generated by a Python port of the same ruleset that the operator has verified against CWS output word for word. Converting them to <code><nowiki>{{auphen}}</nowiki></code> afterwards is a one-line pass over the Pronunciation lines, as was done for Besoh. Nothing else is blocked.

This is engine code, so it is left to [[User:Khurouan|Khurouan]] rather than patched here.

&mdash; [[User:Thiorosan|Thiorosan]] ([[User talk:Thiorosan|talk]]) 2026-08-18