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text.gap-buffer
- Gap bufferThis module provides a gap buffer, a data structure useful for editable text.
A gap buffer is a vector of characters with a “cursor”, where you can insert or delete a character in O(1) time. Most of the editing API operate on the current cursor position.
{text.gap-buffer} Creates a fresh gap buffer and returns it. The initial content is empty.
The keyword argument initial-capacity must be a positive exact integer if given, and specifies the initial capacity of the buffer. The buffer is automatically extended if necessary, so the argument is only a hint; if you know you’ll insert a long string, for example, you can create a buffer that’s large enough to hold it to avoid reallocation overhead.
{text.gap-buffer} Creates a gap buffer that contains the given string, and returns it.
The initial cursor position is set at the end of the string by default.
The pos and whence argument can set the initial
cursor position. The whence argument must be either a symbol
beginning
or a symbol end
, and pos must be an exact
integer offset from the whence. For example, pos = 10 and
whence = beginning
sets the cursor at the 10th character
of the string from the beginning, and pos = -1 and whence =
end
sets the cursor position at one character before the end
of the string. If the combination of pos and whence
points the outside of the string, an error is signaled.
The optional start and end trims the input string before creating the gap buffer.
{text.gap-buffer}
Returns #t
iff obj is a gap buffer.
{text.gap-buffer} Returns a fresh copy of a gap buffer gbuf, with the same content and cursor position.
{text.gap-buffer} Retrieve the content of a gap buffer gbuf as a string or a generator of characters, respectively. The optional start and end arguments are nonnegative exact integers of character index in the content of the buffer, and limits the output within the specified range.
If you modify the content of gap buffer before the returned generator is exhausted, consistent behavior isn’t guaranteed.
{text.gap-buffer} Returns the current cursor position of gbuf, in a nonnegative exact integer.
{text.gap-buffer}
Returns #t
if pos, a position in nonnegative integer,
is at the end of gbuf, #f
otherwise.
{text.gap-buffer} Returns the currently allocated storage size of gbuf, in character count. If you insert more characters into gbuf, the storage is automatically expanded.
{text.gap-buffer} Returns the length of current content of gbuf, in the number of characters.
{text.gap-buffer}
The whence argument must be either a symbol beginning
or a symbol end
. Returns #t
iff the current cursor position
of gbuf is at the beginning or at the end, respectively.
{text.gap-buffer} Returns index-th character of gbuf. If index is out of range, fallback is returned if given, or an error is raised.
{text.gap-buffer} Replaces index-th character of gbuf with char. If index is out of range, an error is signaled.
{text.gap-buffer}
Moves the cursor position of gbuf to a position pos, which
must be an exact integer. The position pos is relative to
whence, which must be either one of the symbols beginning
,
current
or end
. If omitted, beginning
is assumed.
{text.gap-buffer} Inserts content, which must be a character or a string, at the current cursor position of gbuf. The current cursor position is moved to the end of the inserted content.
{text.gap-buffer} Delets size characters from the current cursor position of gbuf. The size argument must be a nonnegative exact integer. It is an error if size overruns.
{text.gap-buffer} Makes gbuf empty.
{text.gap-buffer}
This is a combination of (gap-buffer-delete! gbuf size)
and
(gap-buffer-insert! gbuf content)
.
The size argument must be a nonnegative exact integer,
and the content argument must be either a string or a character.
{text.gap-buffer}
Search a string str in a gap buffer gbuf. If found,
returns the integer index of the beginning of str in gbuf.
If not found, returns #f
.
The optional arguments gstart and gend
restricts the range of gbuf to be searched, by integer indexes.
The default is the entire buffer.
You can pass #f
to indicate to use the
default value.
The optional arguments sstart and send restricts
the span of str to be searched, by integer indexes.
You can pass #f
to indicate to use the
default value.
{text.gap-buffer}
Returns #t
iff the content immeidately following point
matches a string str. If point is omitted or #f
,
the current cursor position is used.
{text.gap-buffer} This is a convenience procedure to “replay” editing of the gap buffer gbuf. The edit-command argument must be either one of the following:
(i pos string)
Insert string at a position pos.
(d pos length)
Delete length characters from a position pos.
(c pos length string)
Change: Deletes length characters from a position pos, then insert string.
Here, pos must be a nonnegative exact integer specifying the position in the gap buffer.
It returns another edit-command that undo the change.
One of the appliations of this procedure is to handle undo/redo list.
(define buf (string->gap-buffer "Hello, World!")) (gap-buffer-edit! buf '(d 0 5)) ⇒ (i 0 "Hello") (gap-buffer-edit! buf '(i 0 "Konnichiwa")) ⇒ (d 0 10) (gap-buffer->string buf) ⇒ "Aloha, World!" ;; Giving the returned values of gap-buffer-edit! in reverse order, ;; you can undo the changes: (for-each (cut gap-buffer-edit! buf <>) '((d 0 10) (i 0 "Hello"))) (gap-buffer->string buf) ⇒ "Hello, World!"
Next: text.gettext
- Localized messages, Previous: text.external-editor
- Running external editor, Up: Library modules - Utilities [Contents][Index]