Making Console Applications: Prompts, Input Options, and Menus

Three lessons in one run: the short form appended ? to 'Your name: ', the prompt form did not, and a line input with no prompt shows nothing at all. Use the prompt form whenever the exact text matters.

key input returns as soon as one key is pressed; the value is that single character. It is the statement for "press any key" pauses and single-letter choices.

The options a program most often reaches for are timeout with elapsed, and eof:

Without eof, reading past the end of input is an error; with it, the variable comes back empty and the flag says why. That is the idiom for a program that reads until its input runs out.

at places the prompt anywhere on the screen. This is the screen image captured while the program waited, with the prompt at row 5, column 10:

Items

• Items are comma-separated. An unquoted item is shown in upper case (apples becomes APPLES); a quoted item keeps its case exactly — "Apples".
• text = value shows the text and returns the value:

• text = { items } is a submenu, nested as deeply as you like. A submenu with no %title of its own is titled with the item's text, as TROPICAL was above.

What the program gets back

• The variable receives the chosen item's value, or its text when it has no value.
• _string$ receives the path of the choice through the levels: #3;#2 means the third item of the top menu, then the second item of its submenu. Rules and headings are not counted.
• Escape (or the Back item of a submenu) leaves the menu with an empty result. Ctrl+Z leaves it too and sets _exit to true — a console application should test that before trusting the result:

Pre-selecting an item, and the other options

• The default option names the item to highlight when the menu opens, by its path — the same form _string$ returns: default '#2' highlights the second choosable item, default '#3;#2' opens the third item's submenu on its second item. Keeping the last _string$ and passing it back as the default reopens a menu on the person's previous choice. A default that is not a path raises the illnum exception.
• timeout and elapsed work with a menu exactly as with a prompt.
• input menu spec$: choice$ is the same statement as line input menu.

The keys a person uses

• Up and Down move the highlight; Delete jumps to the first item.
• Enter, Space, Right arrow, or a click chooses the item, or opens its submenu.
• Escape or Left arrow goes back to the calling menu; from the top menu, Escape leaves with an empty result.
• Ctrl+Z leaves the whole menu and sets _exit.

Layout

Content

Behaviour

Each picture is the screen captured while the menu waited, with the part of the menu string that made the difference. Six directives have no picture because they change behaviour rather than appearance: %message (a status line while the menu is up), %autodisplay, %lockstep, %nomouseover, %inactive and %attached. %title is on every picture, and %heading, %invalid and %split are in the Layout example above.

%at center, center

%size 3 — three rows visible, the rest scroll

%columns 2 — the items split evenly

%items 3 — a new column every three items

%maxwidth 40 — the whole menu capped, the last column cut

%autovbar off — no bars between columns

%vbar — a bar after this column only

%border off — no frame, and so no title

%bar 'text' — a rule that carries a label

%replace — the submenu takes the parent's place

The parent, then the screen after choosing reports: the submenu is where the parent was, not beside it. Its Back item returns.

%menubar — a horizontal bar with pull-downs

%multi — a checklist

%width 40 — a column at least 40 wide

%left — no indent in front of the items

The checked items come back separated by line breaks, so pieces() counts them and piece$() takes them one at a time. The rule: a %multi menu cannot contain submenus. The menu string is refused when it is parsed, and the exception says why: