Pressing down arrow behavior

[vivrekar]

When typing something into the interpreter and you press the down arrow before pressing Enter, the interpreter displays an empty line. Pressing the up arrow displays the previous line, and the "in-progress" line being typed is lost.
Similarly, when you are typing something into the interpreter and press the up arrow before pressing Enter, the interpreter displays the previous line. Pressing the down arrow displays a blank line, and the "in-progress" line being typed is lost.
A possible behavior that is more intuitive is to save the in-progress line being typed when the up or down arrow is clicked. Here are a few scenarios, where the user has typed some input and hasn't pressed Enter yet:

1. User presses up arrow. Previous line input is displayed. User presses down arrow. The "in-progress" line is displayed, instead of an empty line like right now.
2. User presses down arrow. The displayed line does not change, unlike the current behavior which is to show an empty line.