GNU-devel ELPA - ilist


Display a list in an ibuffer way.
ilist- (.sig), 2024-Mar-31, 190 KiB
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To install this package from Emacs, use package-install or list-packages.

Full description

1. About

This is a little library package that can "display a list in an ibuffer fashion". The core functionality it provides is a function that can accept a list, and produce a string showing the contents of the list according to the specifications of columns and groups.

2. Entry point

The one main function this package provides is ilist-string. It is called as follows.

  • LIST is the list that the user wants to display
  • COLUMNS and GROUPS are described in the following sections
  • DISCARD-EMPTY-P determines whether to display empty groups or not
  • SORTER is either nil, or a function with two arguments which returns non-nil if and only if the first argument should be sorted before the second argument. This is used to sort the elements in the list, before grouping happens. To sort groups, see the section on groups.
  • NO-TRAILING-SPACE is non-nil if there should be no trailing whitespaces in the resulting string.

2.1. Columns

Like in Ibuffer, the user can specify columns to display. Each column comprises the following specifications:

  • NAME: The name to display in the header.
  • FUN: A function that will be given the elements of the list (one at a time) that should return a string as the representation of that element in this column.
  • MIN, MAX: The minimal (resp. maximal) width this column takes.
  • ALIGN: Either :left, :right, or :center. How the contents of the column are aligned.
  • ELIDE: If the content of an element takes more space than the MAX, whether to substitute the last few characters of that content by a fixed "eliding string". If this ELIDE is not a string, then it means not to elide, but to truncate the contents.

2.2. Groups

2.2.1. Fixed groups

Like in Ibuffer, we can group elements together in the display. One difference with Ibuffer is that elements that are not in any group are ignored. If one wants a "default" group, specify that explicitly. The specifications of GROUPS are as follows.

  • NAME: The name of the group. This will be enclosed in square brackets and displayed on a separate line.
  • FUN: A function with one argument. If the function returns non-nil, then that element is considered to pertain to the group.

So a default group just uses a function that always returns t, and is put at the end of the list GROUPS.

Empty groups might or might not be displayed, depending on the value of DISCARD-EMPTY-P.

2.2.2. Automatic groups

An automatic filter group is a function that can give labels to elements in a list. These labels will be used to group elements automatically: the elements with the same label will be grouped together, automagically. Besides, an automatic filter group is also responsible for sorting group labels, and for giving a default label, if no labels are specified for some element.

To be precise, an automatic filter group is a function with the signature: (ELEMENT &optional TYPE). The optional argument TYPE says what the caller wants from the function:

  • nil: If it is omitted or nil, the function should just return the label for ELEMENT.
  • default: If it is the symbol default, the function should return a default label.
  • sorter: If it is the symbol sorter, the function should return a function with two arguments, X and Y. This returned function should return a non-nil value if and only if group X should be placed earlier than group Y.

So, for example, the call (FUN t 'default) should produce the default label, (FUN t 'sorter) should return the function used to sort groups, and (FUN ELEMENT) should return the label for ELEMENT, where FUN is an automatic filter group.

2.2.3. Define automatic filter groups

If one wants to define ones own automatic filter group, then the macro ilist-define-automatic-group, or the shorter alias ilist-dag, might come in handy.

In case you wonder, this dag has nothing to do with an directed acyclic graph; it is just an abbreviation to save some typing. The coincidence of the names is a misfortune.

This macro is called as follows.

(ilist-dag NAME DEFAULT SORTER &rest BODY)
  • NAME: This is a string. The resulting function defined by this macro will be named as ilist-automatic-group-NAME.
  • DEFAULT: This is also a string. It is used to label elements for which this automatic group returns nil as its label.

    Why not just let the automatic group function give the default label instead of nil, then? Well, people make mistakes all the time, at least I do. So I think this mechanism can help people to remember give a default label for elements.

  • SORTER: This should be a function, or the symbol of a function.

    This will be used as the sorting function of the group labels. The sorter function should accept two arguments, and should return a non-nil value if and only if the group labelled by the first argument should be displayed before the group labelled by the second argument.

3. Pixel precision

Emacs is old, and its age shows from time to time.

As an example, Emacs usually measures lengths of strings by the numbers of characters contained in the strings. In most situations this is not a problem, but in some cases, for example when the string contains Chinese characters, this measurement is insufficient for the correct alignment inside tables.

In the beginning, I used the function string-width to measure the widths of strings, but as its documentation says, this function only returns an approximation to the actual width. This is changed in the version 0.2 of the package.

Now the package uses the function string-pixel-width to measure the widths of strings in pixels. Since working with actual pixels requires more computation, and as it does not improve the user experience for users who are fine with the approximation provided by string-width, I decide to let the users control whether or not to work with pixels by the variable: ilist-pixel-precision. If this variable is not nil, the package works with pixels rather than characters, and should provide better alignment and truncation.

Moreover, if the value of this variable is the symbol precise, then the paddings will use display properties to produce pixel-exact spaces so that the alignment is precise and perfect. See the Info node "(elisp) Display Property" for more details.

However, on text terminals, this may not work as expected, as Emacs has no control over exact pixels on a text terminal (my guess).

4. Mapping over lines

For the convenience of package-users, this package also provides some auxiliary functions to operate on the displayed list. One is ilist-map-lines. It is called as follows.

  • FUN: The function to execute on each matching line.
  • PREDICATE: This should be a function with no arguments. It will be executed on each line. If it returns non-nil, that line is considered to be matched.
  • START and END limit the range of the mapping.
  • If NO-SKIP-INVISIBLE is non-nil, then we don’t skip invisible lines.

5. Moving

It might be desired to move between the displayed list items in a cyclic manner, that is, assuming the top of the buffer is identified with the bottom of the buffer. So the package provides four functions for moving. These functions all have an argument NO-SKIP-INVISIBLE; if that argument is non-nil, then invisible lines won't skipped.

  • ilist-backward-line
  • ilist-forward-line: Move between lines. One can control whether to skip group headers or to move cyclicly, through the function parameters.
  • ilist-backward-group-header
  • ilist-forward-group-header: Move between group headers.

6. Packages using IList

The packages that use this library IList, which I know of, are listed here:

If you know about other packages that use IList, or if you write a package using IList, it is welcomed to suggest to list those packages here.

Old versions

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