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author cvs
date Mon, 13 Aug 2007 11:36:19 +0200
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1 @c -*-texinfo-*- 1 @c -*-texinfo-*-
2 @c This is part of the XEmacs Lisp Reference Manual. 2 @c This is part of the XEmacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. 3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
4 @c See the file lispref.texi for copying conditions. 4 @c See the file lispref.texi for copying conditions.
5 @setfilename ../../info/eval.info 5 @setfilename ../../info/eval.info
6 @node Evaluation, Control Structures, Symbols, Top 6 @node Evaluation, Control Structures, Symbols, Top
7 @chapter Evaluation 7 @chapter Evaluation
8 @cindex evaluation 8 @cindex evaluation
28 28
29 @node Intro Eval 29 @node Intro Eval
30 @section Introduction to Evaluation 30 @section Introduction to Evaluation
31 31
32 The Lisp interpreter, or evaluator, is the program that computes 32 The Lisp interpreter, or evaluator, is the program that computes
33 the value of an expression that is given to it. When a function 33 the value of an expression that is given to it. When a function
34 written in Lisp is called, the evaluator computes the value of the 34 written in Lisp is called, the evaluator computes the value of the
35 function by evaluating the expressions in the function body. Thus, 35 function by evaluating the expressions in the function body. Thus,
36 running any Lisp program really means running the Lisp interpreter. 36 running any Lisp program really means running the Lisp interpreter.
37 37
38 How the evaluator handles an object depends primarily on the data 38 How the evaluator handles an object depends primarily on the data
431 function, not a symbol. 431 function, not a symbol.
432 432
433 @smallexample 433 @smallexample
434 @group 434 @group
435 ((lambda (arg) (erste arg)) 435 ((lambda (arg) (erste arg))
436 '(1 2 3)) 436 '(1 2 3))
437 @result{} 1 437 @result{} 1
438 @end group 438 @end group
439 @end smallexample 439 @end smallexample
440 440
441 @noindent 441 @noindent
443 symbol function indirection when calling @code{erste}. 443 symbol function indirection when calling @code{erste}.
444 444
445 The built-in function @code{indirect-function} provides an easy way to 445 The built-in function @code{indirect-function} provides an easy way to
446 perform symbol function indirection explicitly. 446 perform symbol function indirection explicitly.
447 447
448 @c Emacs 19 feature 448 @defun indirect-function object
449 @defun indirect-function function 449 This function returns the meaning of @var{object} as a function. If
450 This function returns the meaning of @var{function} as a function. If 450 @var{object} is a symbol, then it finds @var{object}'s function
451 @var{function} is a symbol, then it finds @var{function}'s function 451 definition and starts over with that value. If @var{object} is not a
452 definition and starts over with that value. If @var{function} is not a 452 symbol, then it returns @var{object} itself.
453 symbol, then it returns @var{function} itself.
454 453
455 Here is how you could define @code{indirect-function} in Lisp: 454 Here is how you could define @code{indirect-function} in Lisp:
456 455
457 @smallexample 456 @smallexample
458 (defun indirect-function (function) 457 (defun indirect-function (function)