feat(eval): fold ^ before multiply

[JustNak]

Why

The keypad is four-function. Keyboard users still expect Shift+6 to raise a number to a power. 2 ^ 2 should be 4.

Scope

• Backend::evaluateTokens folds ^ right-to-left, then × ÷, then + −.
• pressKey and isOperator treat ^ as an operator, so dangling-operator replacement and chaining keep working.
• Main.qml accepts ^ from the keyboard. The 4×5 keypad is unchanged.
• 0 ^ 0 and a negative base with a non-integer exponent return Error.
• Percent with pending ^ is x÷100, same as × and ÷.
• README.md documents the key and the fold order.
• Tests in calculatesPowers, percentOfRunningTotal, and evaluatesTokens.

Tradeoffs

• No keypad button. The face stays 4×5. Power is keyboard-only.
• Right-associative ^, so 2 ^ 3 ^ 2 is 512. A left-associative fold would print 64 and surprise anyone who writes math.
• No parser rewrite. The expression stays an alternating token list with one more fold pass.

Blast Radius

Keyboard ^ is new input. Existing + − × ÷ paths still run after the power pass. Percent of running total still applies only to pending + or −.

Verification

• ./bin/test in this tree. 20 passed, 0 failed, including 2 ^ 2, mixed precedence, right-associativity, 0 ^ 0, (-2) ^ 0.5, and 2 ^ 10%.
• ./bin/build produced build/omacalc.
• QML key routing is not under Qt Test. The regex now includes ^. pressKey("^") is what the tests drive.

[greptile-apps]

Greptile Summary

The PR adds keyboard-entered exponentiation with right-associative precedence while retaining the existing alternating-token evaluator design.

• Routes ^ from QML keyboard input into the backend operator lifecycle.
• Folds powers before multiplication, division, addition, and subtraction.
• Documents exponentiation and adds backend coverage for precedence, associativity, percent handling, chaining, and invalid powers.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/backend.cpp	Adds ^ to operator state handling and implements guarded, right-associative power folding before the existing arithmetic passes.
src/Main.qml	Extends the focused keyboard handler to forward the ^ character without changing the on-screen keypad.
tests/tst_omacalc.cpp	Covers exponentiation precedence, associativity, chaining, invalid domains, and percent behavior.
README.md	Documents keyboard exponentiation, evaluation order, and percent semantics with a pending power operator.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[Keyboard input: ^] --> B[Backend::pressKey]
    B --> C[pressOperator]
    C --> D[Alternating expression tokens]
    D --> E[Fold powers right-to-left]
    E --> F[Fold multiplication and division left-to-right]
    F --> G[Fold addition and subtraction]
    G --> H[Formatted result or Error]

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_{Reviews (2): Last reviewed commit: "feat(eval): fold ^ before multiply" | Re-trigger Greptile}

[JustNak]

Closing this in favor of reviewing on the fork first: JustNak#1

[curtislmartin]

I've been wanting this too. Had the same idea, keep as keyboard only.
Hope it makes it in!