170 lines
8.8 KiB
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170 lines
8.8 KiB
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Function CERROR</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="f_error.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_condit.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_check_.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="cerror"><I>Function</I> <B>CERROR</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>cerror</B> <I>continue-format-control datum <TT>&rest</TT> arguments</I> => <I><A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A></I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>Continue-format-control</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#format_control"><I>format control</I></A>. <P>
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<P>
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<I>datum</I>, <I>arguments</I>---<A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designators</I></A> for a <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> of default type <A REL=DEFINITION HREF="e_smp_er.htm#simple-error"><B>simple-error</B></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#cerror"><B>cerror</B></A> effectively invokes <A REL=DEFINITION HREF="f_error.htm#error"><B>error</B></A> on the <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> named by <I>datum</I>. As with any function that implicitly calls <A REL=DEFINITION HREF="f_error.htm#error"><B>error</B></A>, if the <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> is not handled, <TT>(invoke-debugger </TT><I>condition</I><TT>)</TT> is executed. While signaling is going on, and while in the debugger if it is reached, it is possible to continue code execution (i.e., to return from <A REL=DEFINITION HREF="#cerror"><B>cerror</B></A>) using the <A REL=DEFINITION HREF="a_contin.htm#continue"><B>continue</B></A> <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restart</I></A>. <P>
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If <I>datum</I> is a <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A>, <I>arguments</I> can be supplied, but are used only in conjunction with the <I>continue-format-control</I>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(defun real-sqrt (n)
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(when (minusp n)
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(setq n (- n))
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(cerror "Return sqrt(~D) instead." "Tried to take sqrt(-~D)." n))
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(sqrt n))
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(real-sqrt 4)
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=> 2.0
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(real-sqrt -9)
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>> Correctable error in REAL-SQRT: Tried to take sqrt(-9).
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>> Restart options:
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>> 1: Return sqrt(9) instead.
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>> 2: Top level.
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>> Debug> :continue 1
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=> 3.0
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(define-condition not-a-number (error)
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((argument :reader not-a-number-argument :initarg :argument))
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(:report (lambda (condition stream)
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(format stream "~S is not a number."
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(not-a-number-argument condition)))))
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(defun assure-number (n)
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(loop (when (numberp n) (return n))
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(cerror "Enter a number."
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'not-a-number :argument n)
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(format t "~&Type a number: ")
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(setq n (read))
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(fresh-line)))
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(assure-number 'a)
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>> Correctable error in ASSURE-NUMBER: A is not a number.
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>> Restart options:
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>> 1: Enter a number.
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>> 2: Top level.
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>> Debug> :continue 1
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>> Type a number: 1/2
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=> 1/2
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(defun assure-large-number (n)
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(loop (when (and (numberp n) (> n 73)) (return n))
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(cerror "Enter a number~:[~; a bit larger than ~D~]."
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"~*~A is not a large number."
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(numberp n) n)
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(format t "~&Type a large number: ")
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(setq n (read))
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(fresh-line)))
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(assure-large-number 10000)
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=> 10000
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(assure-large-number 'a)
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>> Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.
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>> Restart options:
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>> 1: Enter a number.
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>> 2: Top level.
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>> Debug> :continue 1
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>> Type a large number: 88
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=> 88
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(assure-large-number 37)
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>> Correctable error in ASSURE-LARGE-NUMBER: 37 is not a large number.
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>> Restart options:
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>> 1: Enter a number a bit larger than 37.
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>> 2: Top level.
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>> Debug> :continue 1
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>> Type a large number: 259
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=> 259
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(define-condition not-a-large-number (error)
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((argument :reader not-a-large-number-argument :initarg :argument))
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(:report (lambda (condition stream)
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(format stream "~S is not a large number."
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(not-a-large-number-argument condition)))))
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(defun assure-large-number (n)
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(loop (when (and (numberp n) (> n 73)) (return n))
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(cerror "Enter a number~3*~:[~; a bit larger than ~*~D~]."
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'not-a-large-number
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:argument n
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:ignore (numberp n)
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:ignore n
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:allow-other-keys t)
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(format t "~&Type a large number: ")
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(setq n (read))
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(fresh-line)))
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(assure-large-number 'a)
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>> Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.
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>> Restart options:
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>> 1: Enter a number.
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>> 2: Top level.
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>> Debug> :continue 1
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>> Type a large number: 88
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=> 88
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(assure-large-number 37)
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>> Correctable error in ASSURE-LARGE-NUMBER: A is not a large number.
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>> Restart options:
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>> 1: Enter a number a bit larger than 37.
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>> 2: Top level.
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>> Debug> :continue 1
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>> Type a large number: 259
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=> 259
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_break_.htm#STbreak-on-signalsST"><B>*break-on-signals*</B></A>. <P>
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Existing handler bindings. <P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_error.htm#error"><B>error</B></A>, <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A>, <A REL=DEFINITION HREF="m_handle.htm#handler-bind"><B>handler-bind</B></A>, <A REL=DEFINITION HREF="v_break_.htm#STbreak-on-signalsST"><B>*break-on-signals*</B></A>, <A REL=DEFINITION HREF="e_smp_tp.htm#simple-type-error"><B>simple-type-error</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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If <I>datum</I> is a <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> rather than a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>, the <A REL=DEFINITION HREF="f_format.htm#format"><B>format</B></A> directive <TT>~*</TT> may be especially useful in the <I>continue-format-control</I> in order to ignore the <A REL=DEFINITION HREF="26_glo_k.htm#keyword"><I>keywords</I></A> in the <A REL=DEFINITION HREF="26_glo_i.htm#initialization_argument_list"><I>initialization argument list</I></A>. For example: <P>
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<PRE>
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(cerror "enter a new value to replace ~*~s"
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'not-a-number
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:argument a)
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</PRE>
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</TT> <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss170.htm">FORMAT-STRING-ARGUMENTS:SPECIFY</A><P></UL><HR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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