fix(formula-engine): typed equality for = and <> (closes #68)#107
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Closes #68. Previously `=` and `<>` unconditionally coerced both operands to numbers, so `IF(A1=C3, A2, 0)` returned `#VALUE!` when either cell held text. Switch the equality arm to a typed compare so values are matched within their own type (number/text/bool/empty), with mixed types returning FALSE for `=` and TRUE for `<>` to match Excel and Google Sheets. Text equality is case-insensitive via Unicode-aware `to_lowercase` — also matches Excel/Sheets `=` semantics. Ordering operators (`<`, `<=`, `>`, `>=`) remain numeric-only; the issue defers lexicographic ordering as a separate question, and a test locks in the current behaviour so any future change is explicit. Adds 11 eval-layer unit tests covering text/text, bool/bool, mixed types, the issue's `IF(A1=C3, A2, 0)` example with text cells, and case-insensitivity. Documents the new semantics in `FORMULA_ENTRIES` (a new `=`/`<>` help entry) and in the CHANGELOG under `Unreleased`. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
=and<>now do typed comparison instead of coercing both operands tof64. Closes Equality operator (=) should work on strings #68.FALSEfor=/TRUEfor<>rather than#VALUE!.<,<=,>,>=) remain numeric-only — that's the deferred scope from Equality operator (=) should work on strings #68 and is now tracked separately in Lexicographic ordering for<,<=,>,>=on text #105.eval_ordering_on_text_still_errors) locks in the current ordering-on-text behaviour so any future relaxation is an explicit decision.=/<>entry inFORMULA_ENTRIESdocumenting the type-by-type rules and the case-insensitivity choice.Excel / Sheets parity
Verified by hand against Excel and Google Sheets. Matches:
"foo"="foo"/"foo"="FOO"(case-insensitive) → TRUE1="1"/TRUE="TRUE"/TRUE=1(mixed types) → FALSE1<>"1"→ TRUETwo follow-ups filed for the divergences I found while verifying:
<,<=,>,>=on text #105 — lexicographic ordering for<,<=,>,>=on text""should be equal (matches Excel/Sheets) #106 — empty cell=""should be TRUE (currently FALSE because empty cell-refs coerce to0)Neither is in scope for this PR.
Test plan
cargo test --workspace— 36/36 eval tests pass, 32/32 integration tests passcargo clippy --workspace --all-targets -- -D warningscleancargo fmt --all --checkcleanIF(A1=C3, A2, 0)example with text cells, and case-insensitivity=/<>and ordering tests still pass (no regression)🤖 Generated with Claude Code