This file describes the new Lisp features of Emacs version 19 as first released to the public. For Lisp changes in subsequent Emacs 19 releases, see the file NEWS.

New Features in the Lisp Language

• The new function delete is a traditional Lisp function. It takes two arguments, elt and list, and deletes from list any elements that are equal to elt. It uses the function equal to compare elements with elt.
• The new function member is a traditional Lisp function. It takes two arguments, elt and list, and finds the first element of list that is equal to elt. It uses the function equal to compare each list element with elt. The value is a sublist of list, whose first element is the one that was found. If no matching element is found, the value is nil.
• The new function indirect-function finds the effective function definition of an object called as a function. If the object is a symbol, indirect-function looks in the function definition of the symbol. It keeps doing this until it finds something that is not a symbol.
• There are new escape sequences for use in character and string constants. The escape sequence `\a' is equivalent to `\C-g', the ASCII BEL character (code 7). The escape sequence `\x' followed by a hexidecimal number represents the character whose ASCII code is that number. There is no limit on the number of digits in the hexidecimal value.
• The function read when reading from a buffer now does not skip a terminator character that terminates a symbol. It leaves that character to be read (or just skipped, if it is whitespace) next time.
• When you use a function function as the input stream for read, it is usually called with no arguments, and should return the next character. In Emacs 19, sometimes function is called with one argument (always a character). When that happens, function should save the argument and arrange to return it when called next time.
• random with integer argument n returns a random number between 0 and n-1.
• The functions documentation and documentation-property now take an additional optional argument which, if non-nil, says to refrain from calling substitute-command-keys. This way, you get the exact text of the documentation string as written, without the usual substitutions. Make sure to call substitute-command-keys yourself if you decide to display the string.
• The new function invocation-name returns as a string the program name that was used to run Emacs, with any directory names discarded.
• The new function map-y-or-n-p makes it convenient to ask a series of similar questions. The arguments are prompter, actor, list, and optional help. The value of list is a list of objects, or a function of no arguments to return either the next object or nil meaning there are no more. The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:

  (format prompter object)
  

  where object is the next object to ask about. If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text. The argument actor should be a function of one argument, which is called with each object that the user says yes for. Its argument is always one object from list. If help is given, it is a list (object objects action), where object is a string containing a singular noun that describes the objects conceptually being acted on; objects is the corresponding plural noun and action is a transitive verb describing actor. The default is ("object" "objects" "act on"). Each time a question is asked, the user may enter y, Y, or SPC to act on that object; n, N, or DEL to skip that object; ! to act on all following objects; ESC or q to exit (skip all following objects); . (period) to act on the current object and then exit; or C-h to get help. map-y-or-n-p returns the number of objects acted on.
• You can now "set" environment variables with the setenv command. This works by setting the variable process-environment, which getenv now examines in preference to the environment Emacs received from its parent.