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ADR 0044 - Function batch — accepted per ADR-0043

  • Status: accepted
  • Date: 2026-05-18
  • Spec target: XTL 0.1
  • Affects: spec/language.md function table; src/functions.ts; conformance corpus

Context​

ADR-0043 added the Excel-native preference principle. This ADR applies it to the Tier-1 function-batch backlog (the candidates that surfaced during the JXLS comparison work) and accepts six functions that meet the principle's gate:

FunctionRender-time critical category
UPPER(s)Used in output_file_pattern and __sheet_name_pattern__ to normalize a source value for the filename / sheet-name; also composes with other XTL functions for filter values (e.g., __inputs__[customer])
LOWER(s)Same
TRIM(s)Used in filename / sheet-name patterns and __inputs__ defaulting to strip operator-typed whitespace
IFERROR(value, fallback)Guards #DIV/0! and future error-cell markers inside cell expressions; the renderer is eager, so IFERROR does not catch xtlError throws — for XLOOKUP no-match use its built-in 4-arg fallback instead
IFS(c1, v1, c2, v2, ...)Multi-branch conditional inside cell expressions and output_file_pattern; cleaner than deep IF chains and reaches the filename context (no Excel formula path in a filename pattern)
DATE(year, month, day)Composes a date from __inputs__ integer components for use in output_file_pattern, __sheet_name_pattern__, @sort (comparing against the synthesized date), and __lists__ membership tests

The strongest render-time justification each function shares is the filename / sheet-name pattern context — those patterns are evaluated by XTL before any cell is written, so there is no Excel formula path available there. For pure cell-output use the Excel-formula alternative often exists (=UPPER(B2), =IFS(...)); the function form is what makes these computations reachable in XTL's pre-render contexts.

Known limitation (current parser): @filter accepts only [Column] op literal predicates. Function-call LHS (e.g., @filter UPPER([X]) = "Y") is not currently supported — authors normalize source-side or use a richer comparison value. Extending the parser is a future ADR.

Specification​

UPPER(s), LOWER(s)​

Signature: one argument, returns a string.

Behavior:

  • Convert all letters in s to uppercase / lowercase using ECMAScript String.prototype.toUpperCase() / toLowerCase() (locale-insensitive — see "Locale" below).
  • Empty / null / undefined input returns the empty string.
  • Non-string inputs (numbers, booleans, dates) are first converted to their canonical string form (per ADR-0009) before case conversion. Booleans become TRUE / FALSE already uppercase; numbers and dates stay character-equivalent.

Locale: Unicode default-case-folding only. No Turkish dotless-I, no Greek final-sigma. Authors who need locale-aware case folding handle it host-side in __inputs__ or upstream of the source workbook. (Mirrors ADR-0020 deferred locale collation.)

TRIM(s)​

Signature: one argument, returns a string.

Behavior:

  • Strip leading and trailing Unicode whitespace from s.
  • Internal whitespace is preserved unchanged (Excel's TRIM() collapses runs of internal whitespace; XTL diverges — see "Compatibility" below).
  • Whitespace is the same set as ADR-0007 (ECMAScript \s plus the U+200B / U+FEFF zero-width carve-out; zero-width characters are content, not whitespace).
  • Empty / null / undefined input returns the empty string.

Compatibility: Excel TRIM() also collapses internal runs. XTL keeps the simpler "edges only" form because:

  1. The most common use case is sanitizing source-data leading / trailing whitespace (@filter TRIM([Customer]) = "Acme").
  2. Internal-run collapse can change semantic data (an address with double-space separators).
  3. Authors who want the Excel form can do it in a follow-up cell formula or normalize source-side.

IFERROR(value, fallback)​

Signature: two arguments. Returns either value (if no error marker) or fallback (if value is an XTL error-cell marker).

Behavior:

  • If value is an XTL error-cell marker (currently only #DIV/0! per ADR-0025), return fallback.
  • Otherwise return value unchanged, including 0, false, and the empty string.

Scope (important): XTL's evaluator is eager — both arguments to IFERROR are evaluated before IFERROR runs. If value's evaluation throws an xtlError (e.g., XLOOKUP no-match without its own 4th-arg fallback), the throw propagates past IFERROR; the function only sees values that already evaluated successfully, including error-cell markers. To guard a no-match XLOOKUP, use the function's built-in 4-arg form: XLOOKUP([k], src[k], src[v], "fallback"). IFERROR is the mechanism for division-by-zero and any future error-cell markers added under ADR-0025's extension path.

Difference from IFEMPTY: IFEMPTY checks the value against the empty predicate (ADR-0007). IFERROR checks whether the value is an error-cell marker. Use IFERROR to guard expressions that may produce #DIV/0!. Use IFEMPTY to substitute defaults for blank source cells.

Per ADR-0043: narrowly justified — the catchable case ([A] / [B] divide-by-zero in a cell expression) can be done with =IFERROR(B2/C2, 0) in the output cell. The render-time- critical case that survives the gate is guarded values in filename / sheet-name patterns and __inputs__ defaulting, where Excel formula cannot reach. ADR-0043's retroactive table marks IFERROR as 🟡 borderline; cookbook 16 documents the cell-output Excel-formula path as preferred for pure cell uses.

The function is still accepted (not rejected) because the filename / __inputs__ cases are real and would otherwise require host-side pre-processing.

IFS(c1, v1, c2, v2, ...)​

Signature: even arity ≥ 2. Pairs of (condition, value).

Behavior:

  • Evaluate conditions left-to-right.
  • The first condition that is truthy (per ADR-0008) returns its paired value.
  • If no condition is truthy, raises xl3/eval/no-match. Authors who want a default value supply a trailing TRUE, default pair (the Excel idiom).
  • Odd-arity calls raise xl3/eval/arity-mismatch.

Compatibility: Excel's IFS returns #N/A when no match. XTL chooses an explicit error so authors fix the gap rather than ship #N/A to the output workbook. The TRUE, default idiom is documented in the cookbook.

DATE(year, month, day)​

Signature: three numeric arguments. Returns a Date at UTC midnight.

Behavior:

  • All three arguments coerce to integer per toNumber. Non-finite values raise xl3/eval/type-mismatch.
  • month is 1-based (matching Excel: DATE(2026, 5, 18) is May 18, 2026).
  • Out-of-range month or day values — both positive AND negative — roll over using JS Date semantics (matches Excel's DATE() rollover behavior).
    • DATE(2026, 13, 1) → 2027-01-01 (overflow into next year)
    • DATE(2026, 2, 30) → 2026-03-02 (overflow past February)
    • DATE(2026, -1, 1) → 2025-12-01 (negative month rolls back)
    • DATE(2026, 5, 0) → 2026-04-30 (day 0 rolls back to prior month's last day)
  • Negative year raises xl3/eval/type-mismatch (mirrors Excel's rejection of years < 1900 — but xl3 accepts the full positive integer range; specifically, year 0 is permitted and produces the ECMA-262 date for that calendar year).

Per ADR-0043: justified — DATE composes a date from __inputs__ integer components (e.g., host passes { year: 2026, month: 5 } and the template builds the filter range via DATE(__inputs__[year], __inputs__[month], 1)).

Error catalog​

New code: xl3/eval/no-match for IFS no-match (per ADR-0015's append-only rule).

xl3/eval/type-mismatch (added in ADR-0019 amendment) is reused by DATE argument validation.

Composition with existing functions​

  • IFERROR(XLOOKUP([Account], Customers[Account], Customers[Name]), "Unknown") is the canonical guarded-lookup pattern.
  • IFS([Renewal] > 10000, "VIP", [Renewal] > 1000, "Standard", TRUE, "Lite") is the multi-tier conditional pattern.
  • DATE(YEAR(TODAY()), MONTH(TODAY()), 1) composes the first of the current UTC month.
  • UPPER(TRIM([Customer])) is the canonical normalize-for-filter pattern.

Consequences​

  • The XTL function table grows by 6 entries. All six are ECMAScript / Excel-standard semantics so porters implement them in <50 lines each.
  • The IFS no-match error is the third arity-related error (after xl3/eval/arity-mismatch and the new xl3/eval/no-match).
  • The cookbook recipe ADR-0050 ("XTL function vs Excel formula") uses these functions in side-by-side examples.

References​

  • ADR-0043 — Excel-native preference principle (the gate)
  • ADR-0019 amendment — date arithmetic (sibling batch)
  • ADR-0039 — HYPERLINK (sibling batch)
  • ADR-0024 — function arity policy
  • ADR-0008 — truthiness rules (used by IFS)
  • ADR-0009 — string coercion (used by UPPER/LOWER)
  • ADR-0015 — error code catalog (the new xl3/eval/no-match)
  • ADR-0045 — function batch — rejected per ADR-0043