Build, Edit, and Recompute a Local Calculator Tape

Reviewed concrete example

Make the tape editable, not permanent

The calculator tape page is a line editor for arithmetic state. It supports two different models. Independent expressions calculate each row on its own. Running accumulator begins with one value and carries the exact result through later single-operation steps.

Rows can be added, moved, duplicated, deleted, and recomputed. Those actions remain in the active page and are not a saved revision history. The interface marks stale and dependent rows visibly so an old result is never presented as current after an edit.

Choose independent or dependent lines

Independent mode accepts the same bounded basic grammar as the expression parser. Each row has its own normalized form and result. If row 2 has a syntax error, a valid row 3 can still calculate because it does not depend on row 2.

Running accumulator mode requires row 1 to be a finite starting value. Each later row has an operation selector and one finite operand. The result before a row is the previous valid result, and the result after becomes the next state. A zero divisor blocks that row and all downstream dependencies.

There is no ANS token, variable, or hidden cross-row formula. Dependency is created only by the accumulator mode’s explicit structure.

Worked accumulator tape

Choose Running accumulator. Set row 1 to starting value 10. Add row 2 as + 2.5, row 3 as × 3, and row 4 as − 4.

Row 1 produces 10. Row 2 shows result before 10 and result after 12.5. Row 3 starts from 12.5 and produces 37.5. Row 4 starts from 37.5 and produces final tape result 33.5.

Now edit row 2 from + 2.5 to + 5. Rows 2 through 4 become stale, and First affected line is 2. Recompute from selected produces 15, 45, and final 41. The impact summary says the final exact result changed by 7.5.

The page does not claim that either tape represents a transaction or source document. It only exposes the arithmetic consequence of the edit.

Move and duplicate with dependency awareness

In Independent mode, moving a row changes presentation order but not another row’s result. In Running accumulator mode, moving an operation changes the sequence and may change every later result. The interface marks the moved row and downstream rows stale.

Duplicating an accumulator step repeats the operation with the same operand as a new row. It does not copy the old before/after results. Deleting a row removes that action and recomputes only after an explicit request.

Move up and Move down are disabled at boundaries and explain why. Keyboard controls need visible focus and an accessible row-position announcement.

Handle errors by mode

In Independent mode, an invalid source reports its character span and leaves that line without a result. Other rows remain eligible. In Running accumulator mode, an invalid operand or zero divisor blocks the row and labels every following row “Blocked by line N” until correction.

Recompute from selected uses the last exact valid state before the selected row. If an earlier dependency is stale or invalid, the action directs the user to the first required row rather than using an old value.

Input, row, token, group-depth, and rational-size limits apply. The editor does not truncate a line or silently skip an operation.

Exact state and copied tape

Finite decimals and expressions evaluate as reduced rationals. Visible decimal rounding never becomes the next accumulator input. Final tape result may include an exact fraction and bounded decimal.

Copy tape produces plain text with mode, line numbers, normalized source, exact or labeled displayed result, errors, and a “Local temporary tape” footer. Copy requires a user action and does not create a file, receipt, cloud record, or audit log.

Refresh, tab closure, browser crash, or Clear tape removes the editor state. Clipboard history remains under the device’s control.

Tape versus register and expression tree

The memory tool rehearses one hidden numeric register and its actions. This editor preserves several visible lines. The expression calculator exposes tokens and a tree for one source. The core scratchpad combines live input with a simpler append-only tape.

Use this page when edit impact and line dependency are the intent. It does not import spreadsheets, bank records, receipts, or files and cannot export a durable ledger.

Tape questions

Choose the tape mode, add or edit the lines, and select Recompute the editable tape. Inspect stale and blocked rows, first affected line, exact before-and-after states, and final impact before copying temporary plain text.