Add amsmath's argument-free macros

[kostub]

What and why

The #N template engine (#268) shipped with three one-argument macros. Its substitution reaches only a template's top level, so a macro whose argument sits inside a group — \operatorname{#1} → \mathrm{#1} — is not expressible yet. But a macro with no arguments has nothing to substitute, so its template can be any shape. This PR adds that entire set; it needs no renderer changes and no new atom types.

Macro registry (+builtinMacros)

Command	Template
\implies	\;\Longrightarrow\;
\impliedby	\;\Longleftarrow\;
\iff	\;\Longleftrightarrow\;
\idotsint	\int\cdots\int
\varliminf	\underline{\lim}
\varlimsup	\overline{\lim}
\varinjlim	\underrightarrow{\lim}
\varprojlim	\underleftarrow{\lim}

\implies, \iff and \impliedby already existed as aliases of the bare Long-arrow glyph. amsmath pads all three with \; on each side, which a single symbol atom cannot express — so they move to the macro registry and pick up the padding. That is a rendering change to existing input, not just an addition.

Symbol table (supportedLatexSymbols)

\thinspace (3mu), \medspace (4mu), \thickspace (5mu), \negthinspace (-3mu), \negmedspace (-4mu), \negthickspace (-5mu).

These deliberately do not go through the macro registry: each expands to a single MTMathSpace, which is exactly what the symbol table already stores for \, \> \; \!. Routing one atom through the macro engine would be a parallel mechanism for no gain. amsmath's stretch components (\medspace is 4mu plus 2mu minus 4mu) are dropped — nothing in iosMath stretches.

Behaviour notes

• Serialization. Macros stay command-faithful: \implies round-trips as \implies , not as its expansion. The spacings normalize instead — they come back as \, \> \; \! where a shorthand exists and as \mkern-4.0mu where none does. Rendering is identical either way.
• atomForLatexSymbolName: now returns nil for implies / impliedby, which left the alias table. LaTeX behaviour is unchanged: the builder consults macros before symbols.

Known limitation

amsmath builds the four \var…lim forms out of \mathop, which iosMath has no command for. The expansion is therefore an Ord, so \varliminf_{n} places the subscript to the right of the underlined lim rather than centred underneath. The symbol is correct; the script position is not. Documented at the registry entry and in the changelog. It resolves on its own if the class-override commands (\mathop, \mathbin, …) are ever added.

Tests

swift test: 529 passing, 0 failures (527 before this change).

Two new tests in MTModularArithmeticTest.m, both covering the zero-argument shape, which is new to the engine:

• testZeroArgumentMacroEquivalence — each macro renders identically to its expansion written out by hand, so a drift back to the unpadded arrow fails loudly.
• testZeroArgumentMacroSerializationRoundTrips — a zero-argument macro has no {} to terminate its name, so the trailing space must survive: \implies y must not come back as \impliesy.

No tests were added for the six spacing rows — straight table constants.

testNewAliases in MTMathListBuilderTest.m lost its implies / impliedby rows, which asserted the old bare-arrow behaviour; the two tests above cover them now.

Beyond the suite I typeset all fourteen commands and ran each through serialize → re-parse → serialize; all stable. (\negmedspace serializes to \mkern-4.0mub before a letter, which looks wrong but parses correctly — the unit reader takes exactly two characters.)

🤖 Generated with Claude Code

https://claude.ai/code/session_01CR3o91FfsodPmwJD1s8499

Summary by CodeRabbit

• New Features

  • Added support for argument-free LaTeX macros, including implication, equivalence, repeated-integral, and variable-limit forms.
  • Added thin, medium, thick, and negative spacing commands.
  • Improved macro termination and preservation of trailing spaces.

• Bug Fixes

  • Corrected macro expansion and serialization round trips.
  • Improved spacing behavior for variable-limit operators.

• Documentation

  • Removed the outdated v2.6.0 changelog entry.

[coderabbitai]

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📝 Walkthrough

Walkthrough

The parser now supports named spacing commands and built-in argument-free macros for implication arrows, equivalence arrows, multiple integrals, and variable limits. Tests cover expansion equivalence, macro finalization, alias updates, and serialization.

Changes

Argument-free macro support

Layer / File(s)	Summary
Spacing symbols and macro definitions iosMath/lib/MTMathAtomFactory.m, iosMath/lib/MTMathListBuilder.m	Added named thin, medium, thick, and negative spacing commands. Added built-in expansions for arrows, \idotsint, and variable-limit forms.
Expansion and serialization validation iosMathTests/MTModularArithmeticTest.m, iosMathTests/MTMathListBuilderTest.m, CHANGELOG.md	Updated macro counts and alias coverage. Added expansion, finalization, trailing-space, and serialization round-trip tests. Removed the v2.6.0 changelog entry.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to ede22

This localized change adds zero-argument math macros and spacing symbols, with the supplied checks passing and no actionable merge-blocking risk remaining beyond normal review.

Sequence Diagram(s)

sequenceDiagram
  participant Input
  participant MTMathListBuilder
  participant MTMathAtomFactory
  Input->>MTMathListBuilder: Parse built-in macro
  MTMathListBuilder->>MTMathAtomFactory: Resolve spacing and symbol atoms
  MTMathAtomFactory-->>MTMathListBuilder: Return expanded math atoms

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Title check	✅ Passed	The title clearly and concisely describes the main change: adding amsmath argument-free macros.
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Actionable comments posted: 1

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Inline comments:
In `@iosMathTests/MTModularArithmeticTest.m`:
- Around line 900-935: Add XCTest typesetter-layout coverage for the
zero-argument macros by extending the tests near
testZeroArgumentMacroEquivalence and
testZeroArgumentMacroSerializationRoundTrips. Include assertions for one padded
arrow macro and one variable-limit macro, verifying rendered spacing and script
placement through the existing typesetter/layout testing utilities while
preserving the current parser, finalization, and serialization coverage.

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[kostub]

CodeRabbit review (CLI 0.7.3)

Run locally with coderabbit review --base master and posted here verbatim — the CLI reviews local changes and has no flag to post to a PR itself.

Compare: feature/amsmath-zero-arg-macros → master
Files reviewed: CHANGELOG.md, iosMath/lib/MTMathAtomFactory.m, iosMath/lib/MTMathListBuilder.m, iosMathTests/MTMathListBuilderTest.m, iosMathTests/MTModularArithmeticTest.m

1 finding — Major 1.

---

major [Functional Correctness] — iosMath/lib/MTMathListBuilder.m:1814-1815

Preserve \idotsint as one multiple-integral operator.

This template expands \idotsint into three independent atoms. With \idotsint_{a}^{b}, macro finalization can transfer the scripts to the final \int, instead of keeping them with the complete operator. The expansion also omits amsmath's dedicated integral-dot and integral-kern logic.

Add a dedicated multiple-integral atom or another expansion that preserves one operator and its limits. Add a regression test with limits in both text and display styles.

Minimal regression reproduction offered by CodeRabbit:

MTMathList* list = [MTMathListBuilder buildFromString:@"\\idotsint_{a}^{b}"];
MTMathList* finalized = list.finalized;
XCTAssertNotNil(finalized.atoms.lastObject.subScript);

---

Triage of this finding is in a follow-up comment.

[kostub]

Triage of the CodeRabbit finding — not actionable

I ran CodeRabbit's own reproduction against this branch. Here is what \idotsint_{a}^{b} actually produces (atom type / nucleus, _ and ^ mark attached scripts):

raw          : Macro()_^
finalized    : LargeOp(∫)  Ord(⋯)  LargeOp(∫)_^
serialized   : \idotsint ^{b}_{a}
hand-written : LargeOp(∫)  Ord(⋯)  LargeOp(∫)_^     ← \int\cdots\int_{a}^{b}

1. The repro asserts the behaviour it calls a bug. XCTAssertNotNil(finalized.atoms.lastObject.subScript) passes on this branch. It is a green test, not a failing one, so it does not name a defect.

2. Scripts on the final \int is what amsmath does. amsmath defines \idotsint as two \intops with the dots between them, and the trailing \nolimits puts the limits to the right of the last integral sign — ∫⋯∫ₐᵇ, not centred under the group. Our output matches.

3. Serialization stays command-faithful. The script attaches to the macro atom at parse time and only moves to the last \int during finalized, so \idotsint_{a}^{b} round-trips as \idotsint and not as its expansion. That is the macro-atom design working as intended.

What is real, and small: amsmath inserts a negative kern between the integral signs and the dots (\intkern@), so its ∫⋯∫ sits marginally tighter than ours, which uses default atom spacing. That is a purely visual difference with no numeric invariant to assert, and no input where the output is wrong — just very slightly wide.

On the suggested fix: "add a dedicated multiple-integral atom" is new renderer machinery, which is exactly what this PR is scoped to avoid — every command here is a registry entry with no new atom types. \iint/\iiint already exist as single Unicode glyphs; \idotsint has no such glyph, so an expansion is the only option short of new layout code. Not worth an atom for a sub-point of horizontal kerning.

No code change. Documenting the spacing approximation in the changelog if it's worth calling out at all.

[kostub]

Code review (superpowers:requesting-code-review)

Reviewed 035a9e2..da3b9ed (2 commits, 5 files, +99/-7). I verified every template and mu value against the TeX Live 2025 sources on this machine rather than from memory, measured the real LaTeX output with \sbox/\wd, and probed the parser/typesetter behaviour on a scratch copy of HEAD. swift test: 529 tests, 0 failures.

Strengths

Every one of the eight templates is byte-exact against the real definitions. I checked, not assumed:

Command	Source	Definition	Template
\implies	amsmath.sty:400	\DOTSB\;\Longrightarrow\;	✅
\impliedby	amsmath.sty:401	\DOTSB\;\Longleftarrow\;	✅
\iff	amsopn.sty:91	\DOTSB\;\Longleftrightarrow\;	✅
\idotsint	amsmath.sty:661-666	\intop\intdots@\intop\ilimits@	✅
\varliminf	amsopn.sty:104	\mathop{\@@underline{…lim}}	✅
\varlimsup	amsopn.sty:107	\mathop{\@@overline{…lim}}	✅
\varinjlim	amsopn.sty:98	\rightarrowfill@ under lim	✅ right
\varprojlim	amsopn.sty:101	\leftarrowfill@ under lim	✅ left

Arrow directions on the \var…lim pair are the easy thing to get backwards and they are correct.

The \implies rendering change is provably right, including the part that is easy to get wrong. \; does not replace the automatic relation spacing, it stacks on top of it — glue nodes don't reset the atom-type run in TeX's mlist_to_hlist. Measured in real LaTeX at 10pt:

$x\implies y$            = 38.1989pt
$x\;\Longrightarrow\; y$ = 38.1989pt   <- identical, template is exact
$x\Longrightarrow y$     = 32.64348pt  <- delta 5.555pt = 2 x 5mu

iosMath reproduces the same delta: x\implies y = 73.1622 vs x\Longrightarrow y = 62.0511 at 20pt, difference 11.11 = 2 x 5mu. That works because MTTypesetter.m:643-652 deliberately preserves prevNode/lastType across a space atom — the same TeX semantics. This PR lands \implies on the correct width, which it was not on before.

\idotsint as \int\cdots\int is exact in display style. $\displaystyle\idotsint$ and $\displaystyle\int\cdots\int$ both measure 34.9999pt.

All six mu values are correct (amsmath.sty:168-177): \thinspace→\,→3, \medspace→\:→4, \thickspace→\;→5, and -3/-4/-5 for the negatives. The comment about dropping the stretch components is accurate — \medmuskip really is 4mu plus 2mu minus 4mu.

The zero-argument shape holds up. I probed 30-odd inputs on a scratch build. Everything behaves:

• serialization (MTMathList.m:1856-1861) already had the arguments.count == 0 trailing-space branch at the base commit; this PR is the first thing that actually exercises it, and it now has a test. x\implies y → x\implies y, and \impliesy correctly errors as an unknown command.
• \idotsint_D puts the script on the last \int — which is exactly where amsmath puts it (\ints@c ends \intop\ilimits@).
• nesting (\pmod{\iff}), \sqrt\iff, \frac{\implies}{2}, \overline{\iff}, x^\iff, \mathrm{\iff}, matrices, \finalized idempotency, copy — all correct, no assertions, no crashes.
• macroAtomForCommand: skips the argument loop entirely at count 0, so requiredArgumentWithError: is never reached. Clean.

Removing the three alias rows is safe in the reverse direction, which was the non-obvious risk. +textToLatexSymbolNames (MTMathAtomFactory.m:1050-1088) is built from supportedLatexSymbols only and never consulted aliases, so \Longrightarrow still serializes to \Longrightarrow. I confirmed the forward direction now returns nil for all three, and that nothing else in the tree looks them up.

Routing the spacings through the symbol table rather than the macro engine was the right call — one atom in, one atom out, no MTMacroAtom wrapper to expand, consistent with how \,/\>/\;/\! already live. Good YAGNI discipline.

The comments explain why, not what. The alias-removal note, the stretch-component note, and the \mathop note all answer the question a reader would actually ask. \mathop/\operatorname genuinely do not exist anywhere in iosMath/lib — I checked.

Issues

Critical (Must Fix)

None.

Important (Should Fix)

1. The \var…lim limitation is understated — spacing is wrong too, not just the script position.
iosMath/lib/MTMathListBuilder.m:1817-1821 and CHANGELOG.md:4.

Both say the script position is the only casualty: "the symbol is right, the script position is not" / "draws the right symbol but puts a script to its right". Being an Ord instead of an Op also costs the inter-atom thin space. Measured:

LaTeX:   $\varliminf x$        = 21.27083pt
LaTeX:   $\underline{\lim} x$  = 19.60420pt   <- 3mu narrower
iosMath: \varliminf x          = 39.22
iosMath: \underline{\lim} x    = 39.22        <- identical; the 3mu is missing

So \varliminf x renders 3mu tight against its operand, in every style, script or no script. This matters because the project's bar is that corner cases get documented rather than designed around — a limitation note that names only half the deviation sends the next reader (and the eventual \mathop implementer) looking for the wrong thing. It also under-warns the user who reads the changelog and concludes the non-script case is faithful.

The fix is one sentence, not a code change. Something like: "…because iosMath has no \mathop: the result is an Ord, so a script lands to its right rather than centred underneath, and the 3mu operator spacing before the following operand is missing."

Minor (Nice to Have)

2. testZeroArgumentMacroEquivalence is a mirror of the table it is testing.
iosMathTests/MTModularArithmeticTest.m:882-916.

ZeroArgumentExpansions() restates the eight template strings, and the assertion parses both sides through the same builder. It catches an unaccompanied edit to +builtinMacros, which is real value. But it does not pin the thing the PR is actually about: the amsmath constant 5mu. If someone "fixes" \implies to \,\Longrightarrow\, they will naturally update the mirror in the same edit and the suite stays green.

One extra assertion pins the constant independently of the registry — e.g. for the three arrow macros, assert the finalized list is [Space(5), Relation, Space(5)]. That is not a table-constant test (the project rightly skips those); it is the behavioural constant this whole change exists to get right.

3. \negmedspace / \negthickspace lose their name on serialization.
iosMath/lib/MTMathListBuilder.m:1700-1714.

spaceToCommands has no entry for -4 or -5, so MTMathSpace -appendLaTeXToString: falls to the generic branch: \negmedspace → \mkern-4.0mu. I verified this round-trips stably and renders identically, so there is no data loss — but it is the only one of the six that comes back unrecognisable (\thinspace → \,, \medspace → \> etc. at least land on real short forms, consistent with the existing alias-normalisation precedent). Two rows — @(-4) : @"negmedspace", @(-5) : @"negthickspace" — would make it command-faithful, and the values are currently unclaimed so there is no collision risk. Optional.

4. The atomForLatexSymbolName: behaviour change is not mentioned anywhere.
iosMath/lib/MTMathAtomFactory.m:1031-1034.

+[MTMathAtomFactory atomForLatexSymbolName:@"implies"] (and iff, impliedby) now returns nil; it is a public, documented method. Per the project's own policy only LaTeX behaviour is the compatibility contract, so this is acceptable — but a caller building lists programmatically gets nil where they used to get an atom, and -addAtom: will reject it. A half-sentence in the changelog would cost nothing. Your call; I am not treating this as a blocker.

5. \implies^2 attaches the script one atom earlier than TeX does. (Informational — no action requested.)

The reverse scan in -transferScriptsToExpansion: skips the non-scriptable trailing \; and lands on the arrow, giving \;\Longrightarrow^2\;. Real TeX sees \;\Longrightarrow\;^2 and opens an empty Ord after the trailing space. The iosMath result is arguably the more useful one and is consistent with the engine's existing rule, so I would leave it. Note the code path itself is already covered by testScriptOnModSkipsTrailingSpace (\mod{n\;}^2) — the new macros are the first case where the trailing space comes from the template rather than the argument, but it is the same branch, so I am not asking for a test.

6. \idotsint is 3mu wide in text and script styles. (Informational — no action requested.)

amsmath \mathchoices the dots: display style gets \@cdots, text/script get a tighter {\cdotp}\mkern1.5mu{\cdotp}\mkern1.5mu{\cdotp}. $\idotsint$ = 26.66658pt vs $\int\cdots\int$ = 28.3332pt. A macro expands at parse time, before the style is known — the exact constraint the \pmod changelog entry already documents — so \int\cdots\int is the right choice and display style is exact. Mentioning only so it is on the record.

Recommendations

• Make the fix in issue 1 (one sentence, two places) and merge.
• Consider issue 2's extra assertion while you are in the file; it is three lines and it is the only thing standing between a future edit and a silent return to the unpadded arrow.
• Issues 3-6 are genuinely optional.

Two things I checked specifically because they were called out as risky and found clean, so you can stop worrying about them: the argument-count-zero paths (serialization, copy, script transfer, nesting, -finalized idempotency, error handling) all behave, and the alias removal breaks nothing in the reverse-lookup/serialization direction.

Assessment

Ready to merge? With fixes — one of them, and it is a sentence of prose.

Reasoning: The templates and mu values are exactly right, independently verified against the amsmath and amsopn sources and against measured LaTeX output; \implies now matches real LaTeX to the mu where it previously did not, and no code path assuming argumentCount >= 1 survives contact with the new zero-argument shape. The only substantive defect is that the documented \var…lim limitation names the script position but omits the 3mu operator spacing, which under-describes a deviation the project's own bar says should be documented accurately.

[kostub]

Addressed in ee94a6d.

Important #1 — \var…lim limitation understated. Fixed. Both the registry comment and the changelog now say the expansion is an Ord rather than an Op and name both consequences: the script position and the missing 3mu against the following atom. Documentation only, as you said.

Minor #3 — \negmedspace/\negthickspace serialization. Fixed, two rows in spaceToCommands. This PR is what created the gap: 3, 4, 5 and -3mu all round-trip to their command, and -4/-5 were the only reachable values left falling through to \mkern. MTMathSpace.appendLaTeXToString: already appends the trailing space on the command branch, so \negmedspace b stays separated.

Minor #2 — extra assertion on [Space(5), Relation, Space(5)]. Not taking it. ZeroArgumentExpansions() hardcodes \;\Longrightarrow\;, so dropping the padding from the registry fails testZeroArgumentMacroEquivalence today — the drift you're guarding against is already caught. A second assertion over the same table would be a parallel test for a covered path.

Minor #4 — atomForLatexSymbolName: returning nil for the three names is an Obj-C symbol change, not a LaTeX one, and LaTeX behaviour is this library's compatibility contract. No changelog entry.

Minor #5, #6 — informational, no action, and #6 (\mathchoiced dots in script style) is genuinely unreachable at parse time.

529 tests, 0 failures.