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====== Function BREAK ====== ====Syntax==== * **break** //''&optional'' format-control ''&rest'' format-arguments// → //**[[CL:Constant Variables:nil]]**// ====Arguments and Values==== * //format-control// - a //[[CL:Glossary:format control]]//. The default is //[[CL:Glossary:implementation-dependent]]//. * //format-arguments// - //[[CL:Glossary:format arguments]]// for the //format-control//. ====Description==== **break** //[[CL:Glossary:format|formats]]// //format-control// and //format-arguments// and then goes directly into the debugger without allowing any possibility of interception by programmed error-handling facilities. If the **[[CL:Restarts:continue]]** //[[CL:Glossary:restart]]// is used while in the debugger, **break** immediately returns **[[CL:Constant Variables:nil]]** without taking any unusual recovery action. **break** binds **[[CL:Variables:star-debugger-hook-star|*debugger-hook*]]** to **[[CL:Constant Variables:nil]]** before attempting to enter the debugger. ====Examples==== <blockquote> (break "You got here with arguments: ~:S." '(FOO 37 A)) <e>BREAK: You got here with these arguments: FOO, 37, A. To continue, type :CONTINUE followed by an option number: 1: Return from BREAK. 2: Top level. Debug> :continue 1 Return from BREAK. </e> <r>[[CL:Constant Variables:nil|NIL]]</r> </blockquote> ====Side Effects==== The debugger is entered. ====Affected By==== **[[CL:Variables:star-debug-io-star|*debug-io*]]**. ====Exceptional Situations==== None. ====See Also==== **[[CL:Functions:error|Function ERROR]]**, **[[CL:Functions:invoke-debugger|Function INVOKE-DEBUGGER]]**. ====Notes==== **break** is used as a way of inserting temporary debugging "breakpoints" in a program, not as a way of signaling errors. For this reason, **break** does not take the //continue-format-control// //[[CL:Glossary:argument]]// that **[[CL:Functions:cerror]]** takes. This and the lack of any possibility of interception by //[[CL:Glossary:condition]]// //[[CL:Glossary:handling]]// are the only program-visible differences between **break** and **[[CL:Functions:cerror]]**. The user interface aspects of **break** and **[[CL:Functions:cerror]]** are permitted to vary more widely, in order to accomodate the interface needs of the //[[CL:Glossary:implementation]]//. For example, it is permissible for a //[[CL:Glossary:Lisp read-eval-print loop]]// to be entered by **break** rather than the conventional debugger. **break** could be defined by: <blockquote> ([[CL:Macros:defun]] break (&optional (format-control "Break") &rest format-arguments) ([[CL:Macros:with-simple-restart]] ([[CL:Types:continue]] "Return from BREAK.") ([[CL:Special Operators:let]] (([[CL:Variables:star-debugger-hook-star|*debugger-hook*]] nil)) ([[CL:Functions:invoke-debugger]] ([[CL:Functions:make-condition]] '[[CL:Types:simple-condition]] :format-control format-control :format-arguments format-arguments)))) [[CL:Constant Variables:nil]]) </blockquote> \issue{FORMAT-STRING-ARGUMENTS:SPECIFY} \issue{DEBUGGER-HOOK-VS-BREAK:CLARIFY} \issue{FORMAT-STRING-ARGUMENTS:SPECIFY}