GNU Guile-NCurses 库手册

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"Guile-NCurses是GNU Guile编程语言的一个扩展库，它为Linux系统上的ncurses库提供了绑定。这个库主要用于更新字符屏幕，提供在没有图形界面的情况下创建交互式终端应用程序的功能。文档适用于Guile-NCurses的2.2版本，由Michael L. Gran、Pradeep Padala以及Tom Dickey和ncurses团队共同编写，发布于2017年4月8日。文档的版权由自由软件基金会和Pradeep Padala持有，并遵循GPL许可证条款。" Guile-NCurses是GNU Guile集成开发环境的一个模块，它的核心目标是将ncurses库的功能引入到Guile这种Scheme方言的编程环境中。ncurses库是一个广泛用于Linux和其他类UNIX系统的文本模式用户界面库，它允许程序员在控制台上创建复杂的、带有光标移动和颜色的文本用户界面（TUI）。这个库特别适合于那些在没有图形化窗口系统的情况下运行的程序，如远程服务器上的应用或简单的命令行工具。 Guile-NCurses提供了丰富的API，使得开发者可以轻松地创建和管理屏幕区域、处理键盘输入、绘制文本、颜色和光标操作。例如，通过使用这个库，开发者可以创建菜单、对话框、进度条等元素，从而让终端用户界面更加友好和交互。在使用Guile-NCurses时，开发者可以利用Scheme语言的强大特性，如高阶函数、闭包和动态类型，来编写简洁且可维护的代码。同时，Guile-NCurses的文档详细解释了如何使用这些功能，包括如何初始化ncurses环境，创建窗口和面板，处理事件循环，以及如何定义和使用自定义的用户界面组件。值得注意的是，Guile-NCurses的使用受到GPL（GNU General Public License）的约束，这意味着所有基于此库的软件都必须遵守相同的开源许可条件，即必须保持源代码开放并允许自由分发和修改。文档中明确指出，包含版权信息和许可通知的义务适用于所有副本或软件的实质性部分。 Guile-NCurses是Guile编程语言与ncurses库之间的重要桥梁，为开发者提供了一种在控制台环境下构建复杂用户界面的强大工具。通过学习和使用Guile-NCurses，程序员可以在命令行界面下创建出具有丰富交互性的程序，同时充分利用Scheme语言的灵活性和表达力。

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Chapter 4: Curses Tutorial 9

This brings us to the mysterious (refresh stdscr). Well, when we called addstr, the

data is actually written to an imaginary window, which is not updated on the screen yet.

The job of addstr is to update a few ﬂags and data structures and write the data to a

buﬀer corresponding to stdscr. In order to show it on the screen, we need to call refresh

and tell the curses system to dump the contents on the screen.

The philosophy behind all this is to allow the programmer to do multiple updates on

the imaginary screen or windows and to do a refresh once all the screen update is done.

refresh checks the window and updates only the portion which has been changed. This

improves performance and oﬀers greater ﬂexibility, too. But, it is sometimes frustrating to

beginners. A common mistake committed by beginners is to forget to call refresh after

they did some update through addstr.

4.1.1.3 About endwin

And ﬁnally, don’t forget to end the curses mode. Otherwise your terminal might behave

strangely after the program quits. endwin frees the memory taken by the curses sub-system

and its data structures and puts the terminal in normal mode. This function must be called

after you are done with curses mode.

4.2 Interactive sessions and guile-ncurses-shell

If you would like to try out these functions interactively by typing them into the scheme

shell, instead of typing them and running them as scripts, the program guile-ncurses-

shell can be used. The problem with interactive Guile sessions using curses is that you

are typing into the same screen that curses is trying to manage, which leads to confusing

results. The program guile-ncurses-shell, which must be run on X, starts an interactive

guile session and creates and xterm that will be managed by curses. The results of the curses

function calls will appear in the xterm, instead of in the screen where the interactive guile

session occurs.

Here we’ll try four functions: initscr sets up the screen, addstr writes a string to the

screen, refresh redraws the screen, and endwin frees the screen.

Upon initialization guile-ncurses-shell automatically calls these functions.

(use-modules (ncurses curses))

(define %guile-ncurses-shell-stdscr (initscr))

It loads the ncurses module; initializes the screen; and saves the returned ncurses screen

structure in the variable %guile-ncurses-shell-stdscr. Thus, you do not need to call

(initscr) in your interactive session when you use guile-ncurses-shell.

The ﬁrst thing you want to do is to redeﬁne the name of the standard window to

something more reasonable.

(define win %guile-ncurses-shell-stdscr)

To check and see if the guile-ncurses-shell is working, you can write a string onto the

created xterm.

(addstr win "hello, world!")

(refresh win)

The guile-ncurses-shell communicates with the xterm using a read port and a write port.

If, for some obscure reason, you need to access the read or write port directly, they are stored

Chapter 4: Curses Tutorial 10

in the variables %guile-ncurses-shell-read-port and %guile-ncurses-shell-write-

port.

When exiting an interactive session, by C-D for example, guile-ncurses-shell auto-

matically calls (endwin), so you do not need to call that yourself.

4.3 The Gory Details

Now that we’ve seen how to write a simple curses program, let’s get into the details. There

are many functions that help customize what you see on the screen and many features which

can be put to full use.

Here we go. . .

4.4 Initialization

We now know that to initialize curses the function initscr has to be called. There are

functions which can be called after this initialization to customize our curses session. We

may ask the curses system to set the terminal in raw mode or initialize color or initialize

the mouse, etc. Let’s discuss some of the functions that are normally called immediately

after initscr.

4.4.1 Initialization Functions

4.4.1.1 raw! and cbreak!

Normally the terminal driver buﬀers the characters a user types until a newline or carriage

return is encountered. But most programs require that the characters be available as soon

as the user types them. The functions cbreak! and raw! are used to disable line buﬀering.

The diﬀerence between these two functions is in the way control characters like suspend

(Ctrl-Z), interrupt and quit (Ctrl-C) are passed to the program. In the raw! mode, these

characters are directly passed to the program without generating a signal. In the cbreak!

mode, these control characters are interpreted as any other character by the terminal driver,

allowing Ctrl-C and Ctrl-Z to quit and suspend the program.

4.4.1.2 echo! and noecho!

These functions control the echoing of characters typed by the user to the terminal. noecho!

switches oﬀ echoing. With echoing oﬀ, when a user presses a character, it is not displayed

on the screen.

4.4.1.3 keypad!

This function enables the reading of function keys like F1, F2, arrow keys, etc. Almost every

interactive program enables this, as arrow keys are a major part of any user interface. Do

(keypad! stdscr #t) to enable this feature for the regular screen stdscr (assuming that

stdscr is the variable you used to hold the output of initscr.)

4.4.1.4 halfdelay!

This function is useful when you want to ask the user for input, and if he doesn’t respond

within a certain time, do something else. One possible example would be a timeout at a

password prompt. halfdelay! enables half-delay mode, which is similar to cbreak! mode

Chapter 4: Curses Tutorial 11

in that characters types are immediately available to the program. However, after a period

of time if there is no input, it returns #f.

4.4.2 An example

Let’s write a program that will clarify the usage of these functions.

#!/usr/bin/guile

(use-modules (ncurses curses))

(define stdscr (initscr)) ; Start curses mode

(raw!) ; Line buffering disabled

(keypad! stdscr #t) ; We get F1, F2, etc

(noecho!) ; Don’t echo when we get a keypress

(addstr stdscr "Type any character to see it in bold\n")

(let ((ch (getch stdscr))) ; Read a key press, put it in ’ch’

(addstr stdscr "The pressed key is ")

(if (char? ch) ; If a non-function key is pressed

(addch stdscr (bold ch)) ; print its name

(addchstr stdscr (bold (keyname ch)))) ; Or, print the function

; key name

(refresh stdscr) ; Print it on the real screen

(getch stdscr) ; Wait for user input

(endwin)) ; End curses mode

Hopefully this program is easy to follow even though I used functions that aren’t ex-

plained yet. The procedure getch is used to get a character from the user. If it returns

a character, the user pressed a character key. If it returns a number, the use pressed a

function key. The (bold ch) adds the bold attribute to the character, and addch prints the

character on the screen.

4.5 A word about windows

Before we plunge into the myriad ncurses functions, let me clear a few things about windows.

Windows are explained in detail in the following sections.

A window is an imaginary screen deﬁned by the curses system. A window does not

mean a bordered window which you usually see in GNOME or KDE system. When curses

is initialized, it creates a default window conventionally named stdscr which represents

your 80x25 (or the size of window in which you are running) screen. If you are doing simple

tasks like printing a few strings, reading input, etc., you can safely use this single window

for all of your purposes. You can also create windows and call functions which explicitly

work on the speciﬁed window.

For example, if you call

(addstr stdscr "Hi There!!!")

(refresh stdscr)

Chapter 4: Curses Tutorial 12

It prints the string on stdscr at the present cursor position. Similarly, the call to

refresh works on stdscr only.

Say you have created multiple windows, then you have to call the functions separately on

each window. When you call refresh, you need to call it on the window that was updated.

(addstr win "Hi There!!!")

(refresh win)

For many functions, there are optional key parameters.

(addstr stdscr string) ; Print on stdscr at present

; cursor location

(addstr stdscr string #:y y #:x x) ; Move to (y, x) then print string

4.6 Output functions

I guess you can’t wait any more to see some action. Back to our odyssey of curses functions.

Now that curses is initialized, let’s interact with the world.

There are three primary functions which you can use to output characters and strings

to the screen.

1. addch: output rendered characters

2. addstr: output unrendered strings

3. addchstr: output rendered strings

4.6.1 The addch procedure

The addch function puts a single rendered character into the current cursor location and

advances the position of the cursor. Attributes are explained in detail in later sections of

the document. If a character is associated with an attribute (bold, reverse video, etc.),

when curses prints the character, it is printed with that rendition.

In order to combine a character with some attributes, you have two options:

1. You can explicitly construct a rendered character by passing a simple character through

the rendition functions for the desired attributes:

(bold #\x)

(blink-on (bold-on #\x))

(color 2 #\x)

2. By using functions like attr-set!, attr-on!, attr-off!, you can manipulate the

current attributes of the given window. Once set, the characters printed in the window

are associated with the attributes until it is turned oﬀ.

Additionally, curses provides some special characters for character-based graphics. You

can draw tables, horizontal or vertical lines. Try looking for the procedures beginning with

acs-.

4.6.1.1 Moving the cursor addch

The optional key parameters #:y y #:x x can be used to move the cursor to a given point,

and then print. Thus the calls

(move stdscr row col)

(addch stdscr ch)

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