TASK: Audit existing LAMBDAs for array-lifting support

[jimmytacks]

Origin

Synced from Notion: TASK: Audit existing LAMBDAs for array-lifting support

Content

Problem

Several existing LAMBDAs in the library silently produce wrong results when given array/range inputs instead of scalars. They don't error — they return a single mixed-up value, which is hard to spot and hard to debug. Confirmed: CELLTOPOS(D6:E6) returns 3300017 (a value derived from row of arg 1 + column of arg 2 mashed together) instead of {3300017, 5500028}.

Root cause: bodies use functions that consume an array as a whole (SUMPRODUCT, SEQUENCE(LEN(x)), multi-capture REGEXEXTRACT, etc.) on parameters that may themselves be arrays. The lambda gets called once with the entire array and the aggregator collapses or mis-aligns the cross-product.

For competitive cases this is a silent footgun — you'll reach for a helper, point it at a column, and get a plausible-but-wrong number with the clock running.

Rule for what should lift

• Should lift: any LAMBDA with at least one scalar-shaped input and a scalar-shaped output. Lifting is per-parameter (a parameter that semantically takes one value).
• Can't lift (skip): LAMBDAs with no real inputs (constant-table helpers), or whose output is inherently an array (region/window extractors).

Scope

Review every LAMBDA currently in the library:

• CELLTOPOS, POSTOCELL — coordinate conversion
• MOVECELL, ARROWMOVES, DEFAULTARROWS, DEFAULTMOVEDELTAS, KNIGHTDELTAS — grid movement
• GRIDAREA, GRIDLOOKUP — grid extraction/lookup
• INCEL — INDIRECT shorthand
• (plus any others added between now and execution)

For each, classify as:

1. ✅ Already lifts — pure element-wise body, no action
2. ⚠️ Doesn't lift but should — needs upgrading
3. ➖ Skip — no scalar input (constant helpers) or array output (region extractors)

Approach

Apply the dispatcher pattern (proven working on CELLTOPOS_FIXED):

=LAMBDA(arg, [opts],
  IF(OR(ROWS(arg)>1, COLUMNS(arg)>1),
     MAP(arg, LAMBDA(v, FUNCNAME_SCALAR(v, opts))),
     FUNCNAME_SCALAR(arg, opts)))

Keep the original scalar body as <NAME>_SCALAR (workbook-private helper) and have the public name dispatch. Non-breaking for existing scalar callers; new behaviour for range inputs. The dispatcher must come after the ISOMITTED(...) → ShowHelp branch so =CELLTOPOS() still returns help text.

For LAMBDAs with multiple array-eligible parameters (e.g. MOVECELL(cell, dir)), decide per-function whether to:

• Lift over just the primary arg (simpler, covers most uses)
• Lift over the cartesian product (more powerful, more complex)
• Require equal-shape arrays and zip them (often what's actually wanted)

Initial classification

LAMBDA	Category	Notes
CELLTOPOS	⚠️ Upgrade	SUMPRODUCT(... SEQUENCE(LEN(letters)) ...) collapses array of cell refs
POSTOCELL	⚠️ Verify + upgrade	Uses ADDRESS which doesn't lift cleanly across arrays in all builds
MOVECELL	⚠️ Upgrade	Calls CELLTOPOS internally — may inherit fix; verify after CELLTOPOS upgraded
GRIDLOOKUP	⚠️ Upgrade	Calls CELLTOPOS; value→address branch needs check
INCEL	⚠️ Upgrade	INDIRECT doesn't lift over arrays of addresses
GRIDAREA	➖ Skip	Output is inherently a rectangular array — can't lift
DEFAULTARROWS	➖ Skip	No real input; constant table
DEFAULTMOVEDELTAS	➖ Skip	No real input; constant table
KNIGHTDELTAS	➖ Skip	No real input; constant table
ARROWMOVES	➖ Skip	HSTACK of two constant tables

Deliverable

• Each upgraded LAMBDA replaces the existing definition (same name, same parameter signature, same scalar behaviour)
• A small test sheet in the workbook (or saved snippet) proving each handles {single, array} inputs correctly
• Help text updated to note array support

Notes

• Watch for circular issues: if CELLTOPOS is upgraded first, MOVECELL / GRIDLOOKUP / GRIDAREA may inherit the fix for free in their scalar bodies (since they call CELLTOPOS on a single value). Audit downstream usages before adding redundant dispatchers.
• The investigation that surfaced this is in Book3 / Sheet1 (rows 20–116 are the test grid and findings; rows 121–124 demonstrate the dispatcher pattern working on CELLTOPOS_FIXED).
• Don't break the help-text mechanism (ISOMITTED + ShowHelp).