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Diffstat (limited to 'doc/ref/srfi-modules.texi')
-rw-r--r-- | doc/ref/srfi-modules.texi | 86 |
1 files changed, 62 insertions, 24 deletions
diff --git a/doc/ref/srfi-modules.texi b/doc/ref/srfi-modules.texi index 8a027c00b..df356cc58 100644 --- a/doc/ref/srfi-modules.texi +++ b/doc/ref/srfi-modules.texi @@ -1,6 +1,6 @@ @c -*-texinfo-*- @c This is part of the GNU Guile Reference Manual. -@c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004 +@c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007 @c Free Software Foundation, Inc. @c See the file guile.texi for copying conditions. @@ -1616,24 +1616,61 @@ applied to zero arguments, yields 1. @subsection SRFI-17 - Generalized set! @cindex SRFI-17 -This is an implementation of SRFI-17: Generalized set! +This SRFI implements a generalized @code{set!}, allowing some +``referencing'' functions to be used as the target location of a +@code{set!}. This feature is available from -@findex getter-with-setter -It exports the Guile procedure @code{make-procedure-with-setter} under -the SRFI name @code{getter-with-setter} and exports the standard -procedures @code{car}, @code{cdr}, @dots{}, @code{cdddr}, -@code{string-ref} and @code{vector-ref} as procedures with setters, as -required by the SRFI. +@example +(use-modules (srfi srfi-17)) +@end example + +@noindent +For example @code{vector-ref} is extended so that + +@example +(set! (vector-ref vec idx) new-value) +@end example -SRFI-17 was heavily criticized during its discussion period but it was -finalized anyway. One issue was its concept of globally associating -setter @dfn{properties} with (procedure) values, which is non-Schemy. -For this reason, this implementation chooses not to provide a way to set -the setter of a procedure. In fact, @code{(set! (setter @var{proc}) -@var{setter})} signals an error. The only way to attach a setter to a -procedure is to create a new object (a @dfn{procedure with setter}) via -the @code{getter-with-setter} procedure. This procedure is also -specified in the SRFI. Using it avoids the described problems. +@noindent +is equivalent to + +@example +(vector-set! vec idx new-value) +@end example + +The idea is that a @code{vector-ref} expression identifies a location, +which may be either fetched or stored. The same form is used for the +location in both cases, encouraging visual clarity. This is similar +to the idea of an ``lvalue'' in C. + +The mechanism for this kind of @code{set!} is in the Guile core +(@pxref{Procedures with Setters}). This module adds definitions of +the following functions as procedures with setters, allowing them to +be targets of a @code{set!}, + +@quotation +@nicode{car}, @nicode{cdr}, @nicode{caar}, @nicode{cadr}, +@nicode{cdar}, @nicode{cddr}, @nicode{caaar}, @nicode{caadr}, +@nicode{cadar}, @nicode{caddr}, @nicode{cdaar}, @nicode{cdadr}, +@nicode{cddar}, @nicode{cdddr}, @nicode{caaaar}, @nicode{caaadr}, +@nicode{caadar}, @nicode{caaddr}, @nicode{cadaar}, @nicode{cadadr}, +@nicode{caddar}, @nicode{cadddr}, @nicode{cdaaar}, @nicode{cdaadr}, +@nicode{cdadar}, @nicode{cdaddr}, @nicode{cddaar}, @nicode{cddadr}, +@nicode{cdddar}, @nicode{cddddr} + +@nicode{string-ref}, @nicode{vector-ref} +@end quotation + +The SRFI specifies @code{setter} (@pxref{Procedures with Setters}) as +a procedure with setter, allowing the setter for a procedure to be +changed, eg.@: @code{(set! (setter foo) my-new-setter-handler)}. +Currently Guile does not implement this, a setter can only be +specified on creation (@code{getter-with-setter} below). + +@defun getter-with-setter +The same as the Guile core @code{make-procedure-with-setter} +(@pxref{Procedures with Setters}). +@end defun @node SRFI-19 @@ -2095,10 +2132,10 @@ Conversions @samp{~D}, @samp{~x} and @samp{~X} are not currently described here, since the specification and reference implementation differ. -Currently Guile doesn't implement any localizations for the above, all -outputs are in English, and the @samp{~c} conversion is POSIX -@code{ctime} style @samp{~a ~b ~d ~H:~M:~S~z ~Y}. This may change in -the future. +Conversion is locale-dependent on systems that support it +(@pxref{Accessing Locale Information}). @xref{Locales, +@code{setlocale}}, for information on how to change the current +locale. @node SRFI-19 String to date @@ -2219,9 +2256,10 @@ Notice that the weekday matching forms don't affect the date object returned, instead the weekday will be derived from the day, month and year. -Currently Guile doesn't implement any localizations for the above, -month and weekday names are always expected in English. This may -change in the future. +Conversion is locale-dependent on systems that support it +(@pxref{Accessing Locale Information}). @xref{Locales, +@code{setlocale}}, for information on how to change the current +locale. @end defun |