emacs/doc/misc/vtable.texi

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename ../../info/vtable.info
@settitle Variable Pitch Tables
@include docstyle.texi
@c Merge all indexes into a single Index node.
@syncodeindex fn cp
@syncodeindex vr cp
@syncodeindex ky cp
@c %**end of header

@copying
This file documents the GNU vtable.el package.

Copyright @copyright{} 2022 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License.''

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.''
@end quotation
@end copying

@dircategory Emacs misc features
@direntry
* vtable: (vtable).     Variable Pitch Tables.
@end direntry

@finalout

@titlepage
@title Variable Pitch Tables
@subtitle Columnar Display of Data.

@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top vtable

@insertcopying
@end ifnottex

@menu
* Introduction::        Introduction and examples.
* Concepts::            vtable concepts.
* Making A Table::      The main interface function.
* Commands::            vtable commands.
* Interface Functions:: Interface functions.

Appendices
* GNU Free Documentation License::  The license for this documentation.

Indices
* Index::
@end menu

@node Introduction
@chapter Introduction and Tutorial

Most modes that display tabular data in Emacs use
@code{tabulated-list-mode}, but it has some limitations: It assumes
that the text it's displaying is monospaced, which makes it difficult
to mix fonts and images in a single list.  The @dfn{vtable} (``variable
pitch tables'') package tackles this instead.

@code{tabulated-list-mode} is a major mode, and assumes that it
controls the entire buffer.  A vtable doesn't assume that---you can have
a vtable in the middle of other data, or have several vtables in the
same buffer.

Here's just about the simplest vtable that can be created:

@lisp
(make-vtable
 :objects '(("Foo" 1034)
            ("Gazonk" 45)))
@end lisp

By default, vtable uses the @code{variable-pitch} font, and
right-aligns columns that only have numerical data (and left-aligns
the rest).

You'd normally want to name the columns:

@lisp
(make-vtable
 :columns '("Name" "ID")
 :objects '(("Foo" 1034)
            ("Gazonk" 45)))
@end lisp

Clicking on the column names will sort the table based on the data in
each object (and in this example, each object is just a simple list).

By default, the data is displayed ``as is'', that is, the way
@samp{(format "%s" ...)} would display it, but you can override that.

@lisp
(make-vtable
 :columns '("Name" "ID")
 :objects '(("Foo" 1034)
            ("Gazonk" 45))
 :formatter (lambda (value column &rest _)
              (if (= column 1)
                  (file-size-human-readable value)
                value)))
@end lisp

In this case, that @samp{1034} will be displayed as @samp{1k}---but
will still sort after @samp{45}, because sorting is done on the actual
data, and not the displayed data.

Alternatively, instead of having a general formatter for the table,
you can instead put the formatter in the column definition:

@lisp
(make-vtable
 :columns '("Name"
            (:name "ID" :formatter file-size-human-readable))
 :objects '(("Foo" 1034)
            ("Gazonk" 45)))
@end lisp

The data doesn't have to be simple lists---you can give any type of
object to vtable, but then you also have to write a function that
returns the data for each column.  For instance, here's a very simple
version of @kbd{M-x list-buffers}:

@lisp
(make-vtable
 :columns '("Name" "Size" "File")
 :objects (buffer-list)
 :actions '("k" kill-buffer
            "RET" display-buffer)
 :getter (lambda (object column vtable)
           (pcase (vtable-column vtable column)
             ("Name" (buffer-name object))
             ("Size" (buffer-size object))
             ("File" (or (buffer-file-name object) "")))))
@end lisp

@var{objects} in this case is a list of buffers.  To get the data to be
displayed, vtable calls the @dfn{getter} function, which is called for
each column of every object, and should return something suitable for
display.

Also note the @dfn{actions}: These are simple commands that will be
called with the object under point.  So hitting @kbd{@key{RET}} on a line
will result in @code{display-buffer} being called with a buffer object
as the parameter.  (You can also supply a keymap to be used, but then
you have to write commands that call @code{vtable-current-object} to
get at the object.)

Note that the actions aren't called with the data displayed in the
buffer---they're called with the original objects.

Finally, here's an example that uses just about all the features:

@lisp
(make-vtable
 :columns `(( :name "Thumb" :width "500px"
              :displayer
              ,(lambda (value max-width table)
                 (propertize "*" 'display
                             (create-image value nil nil
                                           :max-width max-width))))
            (:name "Size" :width 10
                   :formatter file-size-human-readable)
            (:name "Time" :width 10 :primary ascend :direction 'descend)
            "Name")
 :objects-function (lambda ()
                     (directory-files "~/pics/redslur/"
                                      t "DSC0000[0-5].JPG"))
 :actions '("RET" find-file)
 :getter (lambda (object column table)
           (pcase (vtable-column table column)
             ("Name" (file-name-nondirectory object))
             ("Thumb" object)
             ("Size" (file-attribute-size (file-attributes object)))
             ("Time" (format-time-string
                      "%F" (file-attribute-modification-time
                            (file-attributes object))))))
 :separator-width 5
 :keymap (define-keymap
           "q" #'kill-buffer))
@end lisp

This vtable implements a simple image browser that displays image
thumbnails (that change sizes dynamically depending on the width of
the column), human-readable file sizes, date and file name.  The
separator width is 5 typical characters wide.  Hitting @kbd{@key{RET}} on a
line will open the image in a new window, and hitting @kbd{q} will
kill a buffer.

@node Concepts
@chapter Concepts

@cindex vtable
A vtable lists data about a number of @dfn{objects}.  Each object can
be a list or a vector, but it can also be anything else.

@cindex getter of a vtable
To get the @dfn{value} for a particular column, the @dfn{getter}
function is called on the object.  If no getter function is defined,
the default is to try to index the object as a sequence.  In any case,
we end up with a value that is then used for sorting.

@cindex formatter of a vtable
This value is then @dfn{formatted} via a @dfn{formatter} function,
which is called with the @dfn{value} as the argument.  The formatter
commonly makes the value more reader friendly.

@cindex displayer of a vtable
Finally, the formatted value is passed to the @dfn{displayer}
function, which is responsible for putting the table face on the
formatted value, and also ensuring that it's not wider than the column
width.  The displayer will commonly truncate too-long strings and
scale image sizes.

All these three transforms, the getter, the formatter and the display
functions, can be defined on a per-column basis, and also on a
per-table basis.  (The per-column transform takes precedence over the
per-table transform.)

User commands that are defined on a table does not work on the
displayed data.  Instead they are called with the original object as
the argument.

@node Making A Table
@chapter Making A Table

@findex make-vtable
The interface function for making (and optionally inserting a table
into a buffer) is @code{make-vtable}.  It takes the following keyword
parameters:

@table @code
@item :objects
This is a list of objects to be displayed.  It should either be a list
of strings (which will then be displayed as a single-column table), or
a list where each element is a sequence containing a mixture of
strings, numbers, and other objects that can be displayed ``simply''.

In the latter case, if @code{:columns} is non-@code{nil} and there's
more elements in the sequence than there is in @code{:columns}, only
the @code{:columns} first elements are displayed.

@item :objects-function
It's often convenient to generate the objects dynamically (for
instance, to make reversion work automatically).  In that case, this
should be a function (which will be called with no arguments), and
should return a value as accepted as an @code{:objects} list.

@item :columns
This is a list where each element is either a string (the column
name), a plist of keyword/values (to make a @code{vtable-column}
object), or a full @code{vtable-column} object.  A
@code{vtable-column} object has the following slots:

@table @code
@item name
The name of the column.

@item width
The width of the column.  This is either a number (the width of that
many @samp{x} characters in the table's face), or a string on the form
@samp{Xe@var{x}}, where @var{x} is a number of @samp{x} characters, or a
string on the form @samp{Xp@var{x}} (denoting a number of pixels), or a
string on the form @samp{X%} (a percentage of the window's width).

@item min-width
This uses the same format as @code{width}, but specifies the minimum
width (and overrides @code{width} if @code{width} is smaller than this.

@item max-width
This uses the same format as @code{width}, but specifies the maximum
width (and overrides @code{width} if @code{width} is larger than this.
@code{min-width}/@code{max-width} can be useful if @code{width} is
given as a percentage of the window width, and you want to ensure that
the column doesn't grow pointlessly large or unreadably narrow.

@item primary
Whether this is the primary column---this will be used for initial
sorting.  This should be either @code{ascend} or @code{descend} to say
in which order the table should be sorted.

@item getter
If present, this function will be called to return the column value.

@defun column-getter object table
It's called with two parameters: the object and the table.
@end defun

@item formatter
If present, this function will be called to format the value.

@defun column-formatter value
It's called with one parameter: the column value.
@end defun

@item displayer
If present, this function will be called to prepare the formatted
value for display.  This function should return a string with the
table face applied, and also limit the width of the string to the
display width.

@defun column-displayer fvalue max-width table
@var{fvalue} is the formatted value; @var{max-width} is the maximum
width (in pixels), and @var{table} is the table.
@end defun

@item align
Should be either @code{right} or @code{left}.
@end table

@item :getter
If given, this is a function that should return the values to use in
the table, and will be called once for each element in the table
(unless overridden by a column getter function).

@defun getter object index table
@c FIXME: Describe the arguments.
For a simple object (like a sequence), this function will typically
just return the element corresponding to the column index (zero-based), but the
function can do any computation it wants.  If it's more convenient to
write the function based on column names rather than the column index,
the @code{vtable-column} function can be used to map from index to name.
@end defun

@item :formatter
If present, this is a function that should format the value, and it
will be called on all values in the table (unless overridden by a
column formatter).

@defun formatter value index table
@c FIXME: The arguments are named, but not explained.  E.g., what is TABLE?
This function is called with three parameters: the value (as returned
by the getter); the column index, and the table.  It can return any
value.

This can be used to (for instance) format numbers in a human-readable
form.
@end defun

@item :displayer
Before displaying an element, it's passed to the displaying function
(if any).

@defun displayer fvalue index max-width table
This is called with four arguments: the formatted value of the element
(as returned by the formatter function); the column index; the display
width (in pixels); and the table.

This function should return a string with the table face applied, and
truncated to the display width.

This can be used to (for instance) change the size of images that are
displayed in the table.
@end defun

@item :use-header-line
If non-@code{nil} (which is the default), display the column names on
the header line.  This is the most common use
case, but if there's other text in the buffer before the table, or
there are several tables in the same buffer, then this should be
@code{nil}.

@item :face
The face to be used.  This defaults to @code{variable-pitch}.  This
face doesn't override the faces in the data, or the faces supplied by
the getter and formatter functions.

@item :actions
This uses the same syntax as @code{define-keymap}, but doesn't refer
to commands directly.  Instead each key is bound to a command that
picks out the current object, and then calls the function specified
with that as the argument.

@item :keymap
This is a keymap used on the table.  The commands here are called as
usual, and if they're supposed to work on the object displayed on the
current line, they can use the @code{vtable-current-object} function
(@pxref{Interface Functions}) to determine what that object is.

@item :separator-width
The width of the blank space between columns.

@item :sort-by
This should be a list of tuples, and specifies how the table is to be
sorted.  Each tuple should consist of an integer (the column index)
and either @code{ascend} or @code{descend}.

The table is first sorted by the first element in this list, and then
the next, until the end is reached.

@item :ellipsis
By default, when shortening displayed values, an ellipsis will be
shown.  If this is @code{nil}, no ellipsis is shown.  (The text to use
as the ellipsis is determined by the @code{truncate-string-ellipsis}
function.)

@findex vtable-insert
@item :insert
By default, @code{make-vtable} will insert the table at point.  If this
is @code{nil}, nothing is inserted, but the vtable object is returned,
and you can insert it later with the @code{vtable-insert} function.
@end table

@node Commands
@chapter Commands
@cindex vtable commands

@c FIXME: Some introductory text is in order?  Commands where?

@table @kbd
@findex vtable-sort-by-current-column
@item S
Sort the table by the current column
(@code{vtable-sort-by-current-column}).  Note that the table is sorted
according to the data returned by the getter function (@pxref{Making A
Table}), not by how it's
displayed in the buffer.  Columns that have only numerical data is
sorted as numbers, the rest are sorted as strings.

@findex vtable-narrow-current-column
@item @{
Make the current column narrower
(@code{vtable-narrow-current-column}).

@findex vtable-widen-current-column
@item @}
Make the current column wider
(@code{vtable-widen-current-column}).

@findex vtable-previous-column
@item M-<left>
Move to the previous column (@code{vtable-previous-column}).

@findex vtable-next-column
@item M-<right>
Move to the next column (@code{vtable-next-column}).

@findex vtable-revert-command
@item g
Regenerate the table (@code{vtable-revert-command}).  This command
mostly makes sense if the table has a @code{:objects-function} that
can fetch new data.
@end table

@node Interface Functions
@chapter Interface Functions

If you need to write a mode based on vtable, you will have to interact
with the table in
various ways---for instance, you'll need to write commands that
updates an object
and then displays the result.  This chapter describes functions for
such interaction.

@defun vtable-current-table
This function returns the table under point.
@end defun

@defun vtable-current-object
This function returns the object on the current line.  (Note that this
is the original object, not the characters displayed in the
buffer.)
@end defun

@defun vtable-current-column
This function returns the column index of the column under point.
@end defun

@defun vtable-goto-table table
Move point to the start of @var{table} and return the position.  If
@var{table} can't be found in the current buffer, don't move point and
return @code{nil}.
@end defun

@defun vtable-goto-object object
Move point to the start of the line where @var{object} is displayed in
the current table and return the position.  If @var{object} can't be found,
don't move point and return @code{nil}.
@end defun

@defun vtable-goto-column index
Move point to the start of the @var{index}th column.  (The first
column is numbered zero.)
@end defun

@defun vtable-beginning-of-table
Move to the beginning of the current table.
@end defun

@defun vtable-end-of-table
Move to the end of the current table.
@end defun

@defun vtable-remove-object table object
Remove @var{object} from @var{table}.  This also updates the displayed
table.
@end defun

@defun vtable-insert-object table object &optional after-object
Insert @var{object} into @var{table}.  If @var{after-object}, insert
the object after this object; otherwise append to @var{table}.  This
also updates the displayed table.
@end defun

@defun vtable-update-object table object old-object
Change @var{old-object} into @var{object} in @var{table}.  This also
updates the displayed table.

This has the same effect as calling @code{vtable-remove-object} and
then @code{vtable-insert-object}, but is more efficient.
@end defun

@defun vtable-column table index
Return the column name of the @var{index}th column in @var{table}.
@end defun

@node GNU Free Documentation License
@chapter GNU Free Documentation License
@include doclicense.texi

@node Index
@unnumbered Index
@printindex cp

@bye