@cindex special forms for control structures
@cindex control structures
- A Lisp program consists of expressions or @dfn{forms} (@pxref{Forms}).
-We control the order of execution of these forms by enclosing them in
-@dfn{control structures}. Control structures are special forms which
-control when, whether, or how many times to execute the forms they
-contain.
+ A Lisp program consists of a set of @dfn{expressions}, or
+@dfn{forms} (@pxref{Forms}). We control the order of execution of
+these forms by enclosing them in @dfn{control structures}. Control
+structures are special forms which control when, whether, or how many
+times to execute the forms they contain.
@cindex textual order
The simplest order of execution is sequential execution: first form
@noindent
This deletes the file named @var{filename}, catching any error and
-returning @code{nil} if an error occurs@footnote{
-Actually, you should use @code{ignore-errors} in such a simple case;
-see below.}.
+returning @code{nil} if an error occurs. (You can use the macro
+@code{ignore-errors} for a simple case like this; see below.)
The @code{condition-case} construct is often used to trap errors that
are predictable, such as failure to open a file in a call to
given error will invoke the debugger only if @code{debug-on-error} and
the other usual filtering mechanisms say it should. @xref{Error Debugging}.
+@defmac condition-case-unless-debug var protected-form handlers@dots{}
+The macro @code{condition-case-unless-debug} provides another way to
+handle debugging of such forms. It behaves exactly like
+@code{condition-case}, unless the variable @code{debug-on-error} is
+non-@code{nil}, in which case it does not handle any errors at all.
+@end defmac
+
Once Emacs decides that a certain handler handles the error, it
returns control to that handler. To do so, Emacs unbinds all variable
bindings made by binding constructs that are being exited, and
@end smallexample
@end defmac
+@defmac with-demoted-errors body@dots{}
+This macro is like a milder version of @code{ignore-errors}. Rather
+than suppressing errors altogether, it converts them into messages.
+Use this form around code that is not expected to signal errors, but
+should be robust if one does occur. Note that this macro uses
+@code{condition-case-unless-debug} rather than @code{condition-case}.
+@end defmac
@node Error Symbols
@subsubsection Error Symbols and Condition Names