commit: #'special-form-p; don't error (thank you Jerry James); flesh out docstring.
changeset: 4335:c32e4dca02960324bf912d7902d8d908d7b2b086
tag: tip
user: Aidan Kehoe <kehoea(a)parhasard.net>
date: Tue Dec 18 23:00:01 2007 +0100
files: src/ChangeLog src/symbols.c
description:
#'special-form-p; don't error (thank you Jerry James); flesh out docstring.
2007-12-18 Aidan Kehoe <kehoea(a)parhasard.net>
* symbols.c (Fspecial_form_p):
Following commentary from Jerry James, don't error if not passed a
subr.
Flesh out the docstring; give details of what a subr is, what a
special form is, and why one should probably not write special
forms oneself.
diff -r cdc2f70d43199e6f413f22bfb4484c18c8ef25f1 -r
c32e4dca02960324bf912d7902d8d908d7b2b086 src/ChangeLog
--- a/src/ChangeLog Tue Dec 18 21:47:27 2007 +0100
+++ b/src/ChangeLog Tue Dec 18 23:00:01 2007 +0100
＠＠ -1,3 +1,13 ＠＠ 2007-12-18 Aidan Kehoe <kehoea＠parhasa
+2007-12-18 Aidan Kehoe <kehoea(a)parhasard.net>
+
+ * symbols.c (Fspecial_form_p):
+ Following commentary from Jerry James, don't error if not passed a
+ subr.
+
+ Flesh out the docstring; give details of what a subr is, what a
+ special form is, and why one should probably not write special
+ forms oneself.
+
2007-12-18 Aidan Kehoe <kehoea(a)parhasard.net>
* symbols.c (Fspecial_form_p): New.
diff -r cdc2f70d43199e6f413f22bfb4484c18c8ef25f1 -r
c32e4dca02960324bf912d7902d8d908d7b2b086 src/symbols.c
--- a/src/symbols.c Tue Dec 18 21:47:27 2007 +0100
+++ b/src/symbols.c Tue Dec 18 23:00:01 2007 +0100
＠＠ -733,14 +733,23 ＠＠ SUBR must be a built-in function.
}
DEFUN ("special-form-p", Fspecial_form_p, 1, 1, 0, /*
-Return whether SUBR is a special form. SUBR must be built-in.
+Return whether SUBR is a special form.
+
+A special form is a built-in function (a subr, that is a function
+implemented in C, not Lisp) which does not necessarily evaluate all its
+arguments. Much of the basic XEmacs Lisp syntax is implemented by means of
+special forms; examples are `let', `condition-case', `defun', `setq' and
so
+on.
+
+If you intend to write a Lisp function that does not necessarily evaluate
+all its arguments, the portable (across emacs variants, and across Lisp
+implementations) way to go about it is to write a macro instead. See
+`defmacro' and `backquote'.
*/
(subr))
{
- subr = indirect_function (subr, 1);
- CHECK_SUBR (subr);
-
- return XSUBR (subr)->max_args == UNEVALLED ? Qt : Qnil;
+ subr = indirect_function (subr, 0);
+ return (SUBRP (subr) && XSUBR (subr)->max_args == UNEVALLED) ? Qt : Qnil;
}
DEFUN ("setplist", Fsetplist, 2, 2, 0, /*
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