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Silence texinfo 5.2 warnings, primarily by adding next, prev, and up pointers to all nodes. See xemacs-patches message with ID <5315f7bf.sHpFD7lXYR05GH6E%james@xemacs.org>.
author Jerry James <james@xemacs.org>
date Thu, 27 Mar 2014 08:59:03 -0600
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5790:dcf9067f26bb 5791:9fae6227ede5
25 * Forms:: How various sorts of objects are evaluated. 25 * Forms:: How various sorts of objects are evaluated.
26 * Quoting:: Avoiding evaluation (to put constants in the program). 26 * Quoting:: Avoiding evaluation (to put constants in the program).
27 * Multiple values:: Functions may return more than one result. 27 * Multiple values:: Functions may return more than one result.
28 @end menu 28 @end menu
29 29
30 @node Intro Eval 30 @node Intro Eval, Eval, Evaluation, Evaluation
31 @section Introduction to Evaluation 31 @section Introduction to Evaluation
32 32
33 The Lisp interpreter, or evaluator, is the program that computes 33 The Lisp interpreter, or evaluator, is the program that computes
34 the value of an expression that is given to it. When a function 34 the value of an expression that is given to it. When a function
35 written in Lisp is called, the evaluator computes the value of the 35 written in Lisp is called, the evaluator computes the value of the
98 effects is @code{(setq foo 1)}. 98 effects is @code{(setq foo 1)}.
99 99
100 The details of what evaluation means for each kind of form are 100 The details of what evaluation means for each kind of form are
101 described below (@pxref{Forms}). 101 described below (@pxref{Forms}).
102 102
103 @node Eval 103 @node Eval, Forms, Intro Eval, Evaluation
104 @section Eval 104 @section Eval
105 @c ??? Perhaps this should be the last section in the chapter. 105 @c ??? Perhaps this should be the last section in the chapter.
106 106
107 Most often, forms are evaluated automatically, by virtue of their 107 Most often, forms are evaluated automatically, by virtue of their
108 occurrence in a program being run. On rare occasions, you may need to 108 occurrence in a program being run. On rare occasions, you may need to
234 @result{} 1 234 @result{} 1
235 @end group 235 @end group
236 @end example 236 @end example
237 @end defvar 237 @end defvar
238 238
239 @node Forms 239 @node Forms, Quoting, Eval, Evaluation
240 @section Kinds of Forms 240 @section Kinds of Forms
241 241
242 A Lisp object that is intended to be evaluated is called a @dfn{form}. 242 A Lisp object that is intended to be evaluated is called a @dfn{form}.
243 How XEmacs evaluates a form depends on its data type. XEmacs has three 243 How XEmacs evaluates a form depends on its data type. XEmacs has three
244 different kinds of form that are evaluated differently: symbols, lists, 244 different kinds of form that are evaluated differently: symbols, lists,
258 Also known as special forms. 258 Also known as special forms.
259 * Autoloading:: Functions set up to load files 259 * Autoloading:: Functions set up to load files
260 containing their real definitions. 260 containing their real definitions.
261 @end menu 261 @end menu
262 262
263 @node Self-Evaluating Forms 263 @node Self-Evaluating Forms, Symbol Forms, Forms, Forms
264 @subsection Self-Evaluating Forms 264 @subsection Self-Evaluating Forms
265 @cindex vector evaluation 265 @cindex vector evaluation
266 @cindex literal evaluation 266 @cindex literal evaluation
267 @cindex self-evaluating form 267 @cindex self-evaluating form
268 268
312 @print{} #<buffer eval.texi> 312 @print{} #<buffer eval.texi>
313 @result{} #<buffer eval.texi> 313 @result{} #<buffer eval.texi>
314 @end group 314 @end group
315 @end example 315 @end example
316 316
317 @node Symbol Forms 317 @node Symbol Forms, Classifying Lists, Self-Evaluating Forms, Forms
318 @subsection Symbol Forms 318 @subsection Symbol Forms
319 @cindex symbol evaluation 319 @cindex symbol evaluation
320 320
321 When a symbol is evaluated, it is treated as a variable. The result 321 When a symbol is evaluated, it is treated as a variable. The result
322 is the variable's value, if it has one. If it has none (if its value 322 is the variable's value, if it has one. If it has none (if its value
346 value of @code{nil} is always @code{nil}, and the value of @code{t} is 346 value of @code{nil} is always @code{nil}, and the value of @code{t} is
347 always @code{t}; you cannot set or bind them to any other values. Thus, 347 always @code{t}; you cannot set or bind them to any other values. Thus,
348 these two symbols act like self-evaluating forms, even though 348 these two symbols act like self-evaluating forms, even though
349 @code{eval} treats them like any other symbol. 349 @code{eval} treats them like any other symbol.
350 350
351 @node Classifying Lists 351 @node Classifying Lists, Function Indirection, Symbol Forms, Forms
352 @subsection Classification of List Forms 352 @subsection Classification of List Forms
353 @cindex list form evaluation 353 @cindex list form evaluation
354 354
355 A form that is a nonempty list is either a function call, a macro 355 A form that is a nonempty list is either a function call, a macro
356 call, or a special form, according to its first element. These three 356 call, or a special form, according to its first element. These three
362 element. This element alone determines what kind of form the list is 362 element. This element alone determines what kind of form the list is
363 and how the rest of the list is to be processed. The first element is 363 and how the rest of the list is to be processed. The first element is
364 @emph{not} evaluated, as it would be in some Lisp dialects such as 364 @emph{not} evaluated, as it would be in some Lisp dialects such as
365 Scheme. 365 Scheme.
366 366
367 @node Function Indirection 367 @node Function Indirection, Function Forms, Classifying Lists, Forms
368 @subsection Symbol Function Indirection 368 @subsection Symbol Function Indirection
369 @cindex symbol function indirection 369 @cindex symbol function indirection
370 @cindex indirection 370 @cindex indirection
371 @cindex void function 371 @cindex void function
372 372
461 (indirect-function (symbol-function function)) 461 (indirect-function (symbol-function function))
462 function)) 462 function))
463 @end smallexample 463 @end smallexample
464 @end defun 464 @end defun
465 465
466 @node Function Forms 466 @node Function Forms, Macro Forms, Function Indirection, Forms
467 @subsection Evaluation of Function Forms 467 @subsection Evaluation of Function Forms
468 @cindex function form evaluation 468 @cindex function form evaluation
469 @cindex function call 469 @cindex function call
470 470
471 If the first element of a list being evaluated is a Lisp function 471 If the first element of a list being evaluated is a Lisp function
485 is written in Lisp, the arguments are used to bind the argument 485 is written in Lisp, the arguments are used to bind the argument
486 variables of the function (@pxref{Lambda Expressions}); then the forms 486 variables of the function (@pxref{Lambda Expressions}); then the forms
487 in the function body are evaluated in order, and the value of the last 487 in the function body are evaluated in order, and the value of the last
488 body form becomes the value of the function call. 488 body form becomes the value of the function call.
489 489
490 @node Macro Forms 490 @node Macro Forms, Special Operators, Function Forms, Forms
491 @subsection Lisp Macro Evaluation 491 @subsection Lisp Macro Evaluation
492 @cindex macro call evaluation 492 @cindex macro call evaluation
493 493
494 If the first element of a list being evaluated is a macro object, then 494 If the first element of a list being evaluated is a macro object, then
495 the list is a @dfn{macro call}. When a macro call is evaluated, the 495 the list is a @dfn{macro call}. When a macro call is evaluated, the
531 Note that the argument @code{(assq 'handler list)} appears in the 531 Note that the argument @code{(assq 'handler list)} appears in the
532 expansion. 532 expansion.
533 533
534 @xref{Macros}, for a complete description of XEmacs Lisp macros. 534 @xref{Macros}, for a complete description of XEmacs Lisp macros.
535 535
536 @node Special Operators 536 @node Special Operators, Autoloading, Macro Forms, Forms
537 @subsection Special Operators 537 @subsection Special Operators
538 @cindex special operator evaluation 538 @cindex special operator evaluation
539 @cindex special form 539 @cindex special form
540 540
541 A @dfn{special operator} (historically, and less logically, a 541 A @dfn{special operator} (historically, and less logically, a
641 doesn't exist in Common Lisp. @code{throw} is a special operator in 641 doesn't exist in Common Lisp. @code{throw} is a special operator in
642 both Common Lisp and XEmacs Lisp (because it must be able to throw 642 both Common Lisp and XEmacs Lisp (because it must be able to throw
643 multiple values).@refill 643 multiple values).@refill
644 @end quotation 644 @end quotation
645 645
646 @node Autoloading 646 @node Autoloading, , Special Operators, Forms
647 @subsection Autoloading 647 @subsection Autoloading
648 648
649 The @dfn{autoload} feature allows you to call a function or macro 649 The @dfn{autoload} feature allows you to call a function or macro
650 whose function definition has not yet been loaded into XEmacs. It 650 whose function definition has not yet been loaded into XEmacs. It
651 specifies which file contains the definition. When an autoload object 651 specifies which file contains the definition. When an autoload object
652 appears as a symbol's function definition, calling that symbol as a 652 appears as a symbol's function definition, calling that symbol as a
653 function automatically loads the specified file; then it calls the real 653 function automatically loads the specified file; then it calls the real
654 definition loaded from that file. @xref{Autoload}. 654 definition loaded from that file. @xref{Autoload}.
655 655
656 @node Quoting 656 @node Quoting, Multiple values, Forms, Evaluation
657 @section Quoting 657 @section Quoting
658 @cindex quoting 658 @cindex quoting
659 659
660 The special operator @code{quote} returns its single argument, as written, 660 The special operator @code{quote} returns its single argument, as written,
661 without evaluating it. This provides a way to include constant symbols 661 without evaluating it. This provides a way to include constant symbols
708 Other quoting constructs include @code{function} (@pxref{Anonymous 708 Other quoting constructs include @code{function} (@pxref{Anonymous
709 Functions}), which causes an anonymous lambda expression written in Lisp 709 Functions}), which causes an anonymous lambda expression written in Lisp
710 to be compiled, and @samp{`} (@pxref{Backquote}), which is used to quote 710 to be compiled, and @samp{`} (@pxref{Backquote}), which is used to quote
711 only part of a list, while computing and substituting other parts. 711 only part of a list, while computing and substituting other parts.
712 712
713 @node Multiple values 713 @node Multiple values, , Quoting, Evaluation
714 @section Multiple values 714 @section Multiple values
715 @cindex multiple values 715 @cindex multiple values
716 716
717 @noindent 717 @noindent
718 Under XEmacs, expressions can return zero or more results, using the 718 Under XEmacs, expressions can return zero or more results, using the