The REPL

The Shape REPL is a notebook-style TUI built on ratatui — not a plain stdin-line prompt. It uses modal editing (Normal / Insert / Command / Inspect) and cell-based history.

Start

shape repl

This drops you into an alternate-screen terminal UI. Each cell has a gutter marker:

• [N] (green) — input cell, not yet executed
• [N]✓ (cyan) — input cell, executed successfully
• ▶ / blank (dark gray) — output cell
• ! (red) — error output
• # (cyan) — chart output

Modes

The REPL is modal in the vim style:

• Normal — navigation, cell selection, commands
• Insert — typing into the focused cell
• Command — typed after :, executes a REPL command on Enter
• Inspect — output-cell inspection

The current mode is shown in the status bar.

Key Bindings (Normal mode)

Key	Action
i	Enter Insert mode in the selected cell
a / A / I	Insert at cursor / end / beginning
o	Open a new input cell below
j / k (or arrows)	Move selection down / up
h / l (or arrows)	Move selection left / right
g g	Go to first cell
G	Go to last cell
x	Cut character
r	Re-run selected cell
d d	Delete selected cell
:	Enter Command mode
q	Quit

Key Bindings (Insert mode)

Key	Action
Esc	Commit the cell and return to Normal mode
Enter	Insert a newline inside the cell
Shift+Enter / Ctrl+Enter	Execute the cell and open a new one below

Command Mode

Press : from Normal mode to enter Command mode, then type one of:

• q / quit — exit the REPL
• clear — clear all cells

Any other input shows Unknown command in the status bar.

A Typical Session

1. Start with shape repl — you land in Normal mode with an empty input cell.
2. Press i to enter Insert mode and type:

   let x = 10
   let y = 5
   x + y

3. Press Shift+Enter to execute. The cell is committed ([0]✓), and a new input cell opens below with the result rendered in an output cell.
4. Press i again to enter the next cell. Type:

   fn square(n: int) -> int { n * n }

   Then Shift+Enter.
5. Open another cell with o, type square(9), then Shift+Enter — the output shows 81.
6. Press :, type q, press Enter to quit (or just press q from Normal mode).

Tips

• Keep cell content small and focused — each cell is one logical unit.
• Validate inferred types with hover/inlay hints in your editor when prototyping larger pieces, then drop them into the REPL.
• Use r to re-execute the selected cell after editing it.

Next Steps

Continue with Variables and Types.