Source Code
In file-systems, Emacs Lisp code exists as plain text files with the filename suffix ".el" (a common exception, the user's init file, often appears or appeared as ".emacs".) When the files are loaded, an interpreter component of the Emacs program reads and parses the functions and variables, storing them in memory. They are then available to other editing functions, and to user commands. Functions and variables can be freely modified and re-loaded.
In order to save time and memory space, much of the functionality of Emacs loads only when required. Each set of optional features is implemented by a collection of Emacs code called a "library". For example, there is a library for highlighting keywords in program source code, and a library for playing the game of Tetris. Each library is implemented using one or more Emacs Lisp source files.
Emacs developers write certain functions in C. These are "primitives", also known as "built-in functions" or "subrs". Although primitives can be called from Lisp code, they can only be modified by editing the C source files and recompiling. In GNU Emacs, primitives are not available as external libraries; they are part of the Emacs executable. In XEmacs, runtime loading of such primitives is possible, using the operating system's support for dynamic linking. Functions may be written as primitives because they need access to external data and libraries not otherwise available from Emacs Lisp, or because they are called often enough that the comparative speed of C versus Emacs Lisp makes a worthwhile difference.
However, because errors in C code can easily lead to segmentation violations or to more subtle bugs, which crash the editor, and because writing C code that interacts correctly with the Emacs Lisp garbage collector is error-prone, relatively few functions are implemented as primitives.
Read more about this topic: Emacs Lisp
Famous quotes containing the words source and/or code:
“By recognizing a favorable opinion of yourself, and taking pleasure in it, you in a measure give yourself and your peace of mind into the keeping of another, of whose attitude you can never be certain. You have a new source of doubt and apprehension.”
—Charles Horton Cooley (1864–1929)
“Wise Draco comes, deep in the midnight roll
Of black artillery; he comes, though late;
In code corroborating Calvin’s creed
And cynic tyrannies of honest kings;
He comes, nor parlies; and the Town, redeemed,
Gives thanks devout; nor, being thankful, heeds
The grimy slur on the Republic’s faith implied,
Which holds that Man is naturally good,
And—more—is Nature’s Roman, never to be
scourged.”
—Herman Melville (1819–1891)