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gridcraft/docs/function-parity.md
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Harrison BoothandClaude Opus 5.5 2aeb21d4d3 Formulas: flat operator chains as long as Excel allows (#916) 
along: =1+1+... with 4,096 operands (8,192 characters, exactly Excel's
limit, which Excel accepts and calculates) overflowed the stack when
entered, because the derived Clone of Expr recursed once per operand
down the chain's left spine. Saving hit the same in the XLSX writer.

- Expr: Clone, PartialEq, walk and map follow the left spine in a loop
  and recurse only into right operands and real nesting.
- XLSX: _xlpm. prefixing and the implicit-intersection scan follow the
  spine too. The scan's depth limit of 64 wrote any chain of more than
  about 64 operands as a dynamic-array formula; such sums are plain
  formulas again (ranges in the chain still get array evaluation).
- Evaluate Formula borrows sub-expressions instead of cloning each
  operator's subtree (quadratic memory on a long chain).
- Spanish formula entry and display no longer refuse chains of more
  than 256 operands; the left spine does not count as nesting.

Tests run on a 1 MiB stack (the Windows main thread) with Excel's
observed results: formula (clone/eq/walk/map/adjust at 4,096), calc
(401 and 4,096 operands, -, *, /, ^, &, %, comparisons, 1,500 refs),
xlsx (long chains written as scalar formulas), engine (cell.set, fill,
copy/paste, insert rows/columns, undo/redo, Evaluate Formula, XLSX save
and reopen), Spanish entry. Each fails without the fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-19 18:54:30 -05:00

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# Function parity: worksheet functions and formulas
> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-15 · **Change:** minor (flat operator chains as long as Excel allows: 4,096 operands no longer overflow the stack, Spanish entry accepts them, files keep them as plain formulas); previously minor (MEDIAN and AGGREGATE median avoid intermediate overflow) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
Excel's worksheet functions, category by category, against GridCraft's function library. Part of
[target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
## How this is measured
- **Excel's list (523):** Microsoft's "Excel functions (alphabetical)" support page, fetched and
parsed on 2026-10-10 (506 rows with their category and the Excel version that introduced
them), plus 14 text functions the page lists under combined entries (FIND/FINDB, LEFT/LEFTB,
LEN/LENB, MID/MIDB, REPLACE/REPLACEB, RIGHT/RIGHTB, SEARCH/SEARCHB), BETA.INV, and COPILOT and
PY (Microsoft 365 functions not on that page when fetched).
- **Ours (505):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
- **Ours (503):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
- **Ours (502):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
- **Ours (502):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
- **Ours (505):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
evaluator's special forms in `crates/calc/src/eval.rs` (`SPECIAL_FUNCTIONS`: IF, IFS, CHOOSE,
OFFSET, INDIRECT, INDEX, SUBTOTAL, AGGREGATE, TEXT, LET, LAMBDA, MAP, REDUCE, SCAN, BYROW, BYCOL,
MAKEARRAY…), excluding the test-only `ADD2`. Every one is an Excel name.
- **Not on Microsoft's list:** USDOLLAR, a legacy function Excel still evaluates (like DOLLAR),
is in our library as a Compatibility function for files that use it. It is not counted above.
- **Working** excludes stubs that return an error by design: the 7 CUBE functions (`#N/A`, no
cube connections) and WEBSERVICE and FILTERXML (`#VALUE!`). Excel for Mac also lacks
WEBSERVICE and FILTERXML; Excel for Windows has them.
- The measurement is **presence**. Depth (edge cases matching Excel) is estimated below.
## Coverage
**Measured: 513 / 523 by name (98.1%); 504 / 523 working (96.4%).**
| Category | Excel | Ours | Working | % working | Missing |
|---|---|---|---|---|---|
| Statistical | 111 | 111 | 111 | 100% | — |
| Math and trigonometry | 80 | 79 | 79 | 99% | PERCENTOF |
| Financial | 55 | 55 | 55 | 100% | — |
| Engineering | 54 | 54 | 54 | 100% | — |
| Text | 50 | 48 | 48 | 96% | DETECTLANGUAGE, TRANSLATE |
| Lookup and reference | 40 | 36 | 36 | 90% | GETPIVOTDATA, IMAGE, RTD, TRIMRANGE |
| Compatibility | 40 | 40 | 40 | 100% | — |
| Date and time | 25 | 25 | 25 | 100% | — |
| Information | 22 | 21 | 21 | 95% | STOCKHISTORY |
| Logical | 19 | 19 | 19 | 100% | — |
| Database | 12 | 12 | 12 | 100% | — |
| Cube | 7 | 7 | 0 | 0% | (all 7 are `#N/A` stubs) |
| Web | 3 | 3 | 1 | 33% | (WEBSERVICE, FILTERXML are stubs; ENCODEURL works) |
| Add-in and Automation | 3 | 1 | 1 | 33% | CALL, REGISTER.ID |
| AI and Python | 2 | 0 | 0 | 0% | COPILOT, PY |
| **Total** | **523** | **505** | **496** | **94.8%** | 18 missing, 9 stubs |
By the Excel version that introduced them (working / total): before 2010 346 / 360, 2010
56 / 56, 2013 49 / 51, 2016 1 / 5, 2019 6 / 6, 2021 11 / 11, 2024 22 / 23, Microsoft 365 5 / 11.
Dynamic-array and LAMBDA-era functions (FILTER, SORT, UNIQUE, XLOOKUP, VSTACK, TAKE, GROUPBY,
PIVOTBY, REGEXTEST…) are all present.
### Scope of what's missing
| Function(s) | In scope? | Estimate | Note |
|---|---|---|---|
| FORECAST.ETS family (4) | yes | 4–6 h | AAA exponential smoothing with seasonality detection; needed for Forecast Sheet too |
| ODDFPRICE, ODDFYIELD, ODDLPRICE, ODDLYIELD | yes | 2–4 h | Odd first/last period bond maths |
| GETPIVOTDATA | yes | 2–3 h | Needs the pivot engine's result cache; also the "Generate GetPivotData" option |
| IMAGE | yes | 3–5 h | Pictures in cells (see PR #105); fetching URLs needs a privacy decision |
| CUBE* (7), WEBSERVICE, FILTERXML | partly | 4–8 h | FILTERXML can work offline; CUBE needs an OLAP/data-model source |
| TRANSLATE, DETECTLANGUAGE, STOCKHISTORY, COPILOT, PY | no (cloud) | — | Microsoft cloud services; open equivalents only by owner decision |
| CALL, REGISTER.ID, RTD | no | — | Native DLL/COM calls; not portable or safe |
## Formula language
| Feature | Status |
|---|---|
| A1 and R1C1 references, absolute/relative/mixed, F4 cycling | done |
| 3-D references (`Sheet1:Sheet3!A1`) | done; endpoint-deletion bug (#140) |
| Structured references (`Table1[Col]`, `[#Totals]`, `@`; the unbracketed `[[#This Row],Col]` some writers emit) | done |
| Defined names (workbook and sheet scope), Create from Selection | done |
| Dynamic arrays, spill, `#SPILL!`, spill operator `A1#` | done; stale-spill bugs (#133, #139; PRs #148, #157) |
| Recalculation after clearing large sparse ranges | every stored cell changed by Clear is reported to recalculation, without a million-coordinate cutoff; removed formula spills are cleared, and removing empty merges still unblocks spills (#1032) |
| Implicit intersection `@`, legacy CSE array formulas | done; legacy array range fill (PR #156) |
| Trim references `A1:.E10` (trailing), `A1.:E10` (leading), `A1.:.E10` (both), also on whole rows/columns (`A:.A`) | done; evaluated as `TRIMRANGE(range, code, code)`, adjusted on insert/delete; files store `_xlfn.TRIMRANGE(range,code,code)` (Excel's own file spelling unconfirmed in public docs), `_xlfn._TRO_ALL/_TRO_LEADING/_TRO_TRAILING(...)` read too |
| LET, LAMBDA, named LAMBDAs, ISOMITTED, MAP/REDUCE/SCAN/BYROW/BYCOL/MAKEARRAY | done |
| Iterative calculation for circular references | done: with Enable Iterative Calculation on (`formulas.calculationOptions` `{iterative, maxIterations, maxChange}`, saved as `<calcPr iterate iterateCount iterateDelta>`), loops are evaluated again from their previous values (blank = 0) until no cell on a loop changes by Maximum Change or Maximum Iterations is reached; off, cycles give `#CIRC!`. Differences: no Options dialog yet (command only); GridCraft recalculates on open, so a loop that never settles (`=A1+1`) advances again each time the file is opened |
| 15-significant-digit comparison semantics | **missing** (#57: `=0.1+0.2=0.3` is FALSE) |
| External workbook references (`[Book.xlsx]Sheet1!A1`) | parsed; links dropped on open, no update |
| Localized function names and `;` separators | **missing** (#45); en-US only |
| Long flat operator chains (`=A1+A2+…`, `-`, `*`, `/`, `^`, `&`, comparisons) | done: no operand limit below Excel's 8,192-character formula limit (Excel, observed: `=1+1+…` with 4,096 operands is exactly 8,192 characters with the `=` and calculates; one more character is refused). Evaluated (#484), printed (#628), stored, copied, adjusted, saved and reopened without recursing once per operand, on a 1 MiB stack (#916); written to XLSX as plain formulas, not dynamic arrays; Spanish entry accepts them |
| Error values | the seven classic errors plus `#SPILL!`, `#CALC!`, `#GETTING_DATA` done; `#FIELD!`, `#BLOCKED!`, `#CONNECT!`, `#BUSY!`, `#UNKNOWN!`, `#PYTHON!` missing (minor: they come from data types, cloud and Python features) |
## Depth (estimated)
**~82% ready.** The library is broad and has 96 test functions in `crates/functions` with many
assertions each, but there is no conformance suite against Excel-computed results, and user
reports keep finding edge cases: MIN() with no arguments (#138), COUNTBLANK past the used range
(#137), ROUND at 15 digits and DATE(1900,2,29) (fixed 10-09), SUMIF sum-range sizing (fixed
10-09). Statistical distributions and financial functions with iterative solvers (RATE, IRR,
XIRR, YIELD) are the highest-risk for last-digit differences.
TEXT() and cell display share `crates/numfmt`; checked against Excel-cached results in
number- and text-format test workbooks (352 TEXT cells), all match:
fraction sections with literal text (`#\:#=/=#`, `#_#/#`), zero fractions, zero-padded
denominators, `?` placeholders padding the thousands separator, and booleans through the text
section (`TEXT(TRUE,";;;\@@\@")` = `@TRUE@`).
`MEDIAN` and `AGGREGATE` function number 12 use an overflow-safe midpoint for even-sized
inputs, so large finite middle values do not become `#NUM!` merely because their sum overflows (#1579).
Sorting, argument coercion and error propagation are unchanged; this is a numerical correction
under the documented median rule, not an extreme-value comparison against desktop Excel.
Work to close (16–26 h in total): the in-scope missing functions (10–16 h with the table above),
an oracle corpus of Excel-computed results per function (owner runs Excel on generated
workbooks; results checked in as data, not Excel files) and fixing what it finds (6–10 h).
## Revision history
| Date | Change | Summary |
|---|---|---|
| 2026-10-14 | minor | Long flat operator chains (#916): 4,096 operands (Excel's 8,192-character limit) no longer overflow the stack when entered, filled, adjusted or saved; chains past 64 operands are no longer saved as dynamic-array formulas; Spanish entry no longer refuses chains past 256 operands |
| 2026-10-15 | minor | MEDIAN and AGGREGATE median use an overflow-safe midpoint (#1579); regressions cover finite extremes, tiny values and dependent recalculation |
| 2026-10-13 | minor | Clear reports changed stored cells sparsely, including those beyond the first million coordinates; dependent formulas and removed spills update, while clearing empty merges still unblocks spills (#1032) |
| 2026-10-12 | minor | USDOLLAR added as a Compatibility function (not on Microsoft's list, so the counts don't change); MIRR with no positive flow is -1, COUNTIF's bare `"<="` / `">="` skip empty strings, INDIRECT with `a1` = FALSE gives `#REF!` for A1-style text (#738) |
| 2026-10-11 | minor | TEXT / number formats fixed against Excel-cached results: fraction literals and zero fractions, `0` denominators zero padded, `?` pads the thousands separator, booleans use the text section (226 mismatches → 0 in 352 TEXT cells) |
| 2026-10-11 | minor | Iterative calculation: circular references iterate up to Maximum Iterations / Maximum Change when enabled |
| 2026-10-11 | minor | Trim-reference operators (`:.`, `.:`, `.:.`) and unbracketed `[[#This Row],Col]` done; dropped the stale "Scope of what's missing" rows for TRIMRANGE, PERCENTOF, BAHTTEXT and the trim references |
| 2026-10-11 | minor | Fixes from the cached-value oracle (`gridcraft-cli check`): MODE / MODE.SNGL / MODE.MULT give `#VALUE!` for text in a direct argument or single-cell reference; `VALUE("")` is `#VALUE!`; SUMPRODUCT with a text scalar argument is `#VALUE!`; ADDRESS leaves `[Book]Sheet` unquoted; VLOOKUP / HLOOKUP / LOOKUP / MATCH approximate match bisect like Excel on unsorted mixed-type data; XLOOKUP / XMATCH binary search compares across types in sort order; SUBTOTAL leaves out filtered rows for every function number (table and sheet AutoFilters) |
| 2026-10-11 | minor | ODDFPRICE, ODDFYIELD, ODDLPRICE, ODDLYIELD added: Financial 55 / 55; 505 / 523 by name, 496 working |
| 2026-10-11 | minor | PERCENTOF and EUROCONVERT added: 503 / 523 by name, 494 working |
| 2026-10-11 | minor | BAHTTEXT added: 502 / 523 by name, 493 working |
| 2026-10-11 | minor | TRIMRANGE added (the trim-reference operators not yet): 502 / 523 by name, 493 working |
| 2026-10-11 | minor | FORECAST.ETS, .CONFINT, .SEASONALITY, .STAT added (AAA exponential smoothing; Excel's optimiser is undocumented, so last digits on noisy data may differ): 505 / 523 by name, 496 working |
| 2026-10-10 | major | Created: 501 / 523 by name, 492 working, per category, against Microsoft's published list |
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