ht.el

The missing hash table library for Emacs.

Functions

• ht-create (test?)
• ht-get (table key default?)
• ht-set (table key value)
• ht-update (table table)
• ht-merge (&rest tables)
• ht-remove (table key)
• ht-clear (table)
• ht-keys (table)
• ht-values (table)
• ht-items (table)
• ht-map (function table)
• ht-each (function table)
• ht-copy (table)
• ht-from-alist (alist)
• ht-from-plist (plist)
• ht-to-alist (table)
• ht-to-plist (table)
• ht-p (table-or-object)
• ht-contains-p (table key)
• ht-size (table)
• ht-empty? (table)
• ht-select (function table)
• ht-reject (function table)
• ht-delete-if (function table)
• ht-find (function table)

Macros

• ht (&rest pairs)
• ht-amap (form table)
• ht-aeach (form table)

Examples

Creating a hash table and accessing it:

(require 'ht)

(defun say-hello (name)
  (let ((greetings (ht ("Bob" "Hey bob!")
                       ("Chris" "Hi Chris!"))))
    (ht-get greetings name "Hello stranger!")))

This could be alternatively written as:

(require 'ht)

(defun say-hello (name)
  (let ((greetings (ht-create)))
    (ht-set greetings "Bob" "Hey Bob!")
    (ht-set greetings "Chris" "Hi Chris!")
    (ht-get greetings name "Hello stranger!")))

Why?

Libraries like s.el (strings) and dash.el (lists) have shown how much nicer Emacs lisp programming can be with good libraries. ht.el aims to similarly simplify working with hash tables.

Common operations with hash tables (e.g. enumerate the keys) are too difficult in Emacs lisp.

ht.el offers:

• A consistent naming scheme (contrast make-hash-table with puthash)
• A more natural argument ordering
• Mutation functions always return nil
• A more comprehensive range of hash table operations, including a conventional map (ht-map returns a list, elisp's maphash returns nil).

Similar libraries

• kv.el (focuses more on alists)

Installation

ht.el is availabe on MELPA and Marmalade.

Add a package archive to your .emacs.d/init.el:

(require 'package)
(add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/") t)

then run M-x package-install <RET> ht <RET>

API changelog

ht.el uses semantic versioning, so an incompatible API change will result in the major version increasing. See CHANGELOG.md for a history of all changes.

The following changes were backwards incompatible:

v1.0

• ht-map now returns a list.

Running tests

M-x ht-run-tests

What's an alist/plist?

An alist is an association list, which is a list of pairs. It looks like this:

((key1 . value1)
 (key2 . value2)
 (key3 . value3))

An alist can also look like this:

((key1 . value1)
 (key2 . value2)
 (key1 . oldvalue))

A plist is a property list, which is a flat list with an even number of items. It looks like this:

(key1 value1
 key2 value2
 key3 value3)

Both of these are slow. ht.el provides ht-from-alist and ht-from-plist to help you convert to hash tables. If you need to work with an alist or plist, use the functions ht-to-alist and ht-to-plist to convert an hash table to those formats.