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cl:functions:read-char-no-hang [2019/09/14 05:00] |
cl:functions:read-char-no-hang [2020/08/05 18:00] (current) |
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| + | ====== Function READ-CHAR-NO-HANG ====== | ||
| + | |||
| + | ====Syntax==== | ||
| + | * **read-char-no-hang** ''&optional'' //input-stream// //eof-error-p// //eof-value// //recursive-p// → //char// | ||
| + | |||
| + | ====Arguments and Values==== | ||
| + | * //input-stream// -- an //[[CL:Glossary:input]]// //[[CL:Glossary:stream designator]]//. The default is //[[CL:Glossary:standard input]]//. | ||
| + | * //eof-error-p// - a //[[CL:Glossary:generalized boolean]]//. The default is //[[CL:Glossary:true]]//. | ||
| + | * //eof-value// - an //[[CL:Glossary:object]]//. The default is **[[CL:Constant Variables:nil]]**. | ||
| + | * //recursive-p// - a //[[CL:Glossary:generalized boolean]]//. The default is //[[CL:Glossary:false]]//. | ||
| + | * //char// - a //[[CL:Glossary:character]]// or **[[CL:Constant Variables:nil]]** or the //eof-value//. | ||
| + | |||
| + | ====Description==== | ||
| + | **read-char-no-hang** returns a character from //input-stream// if such a character is available. If no character is available, **read-char-no-hang** returns **[[CL:Constant Variables:nil]]**. | ||
| + | |||
| + | If //recursive-p// is //[[CL:Glossary:true]]//, this call is expected to be embedded in a higher-level call to **[[CL:Functions:read]]** or a similar //[[CL:Glossary:function]]// used by the //[[CL:Glossary:Lisp reader]]//. | ||
| + | |||
| + | If an //[[CL:Glossary:end of file]]// occurs and //eof-error-p// is //[[CL:Glossary:false]]//, //eof-value// is returned. | ||
| + | |||
| + | ====Examples==== | ||
| + | <blockquote> | ||
| + | ([[CL:Macros:defun]] test-it () | ||
| + | ([[CL:Functions:unread-char]] ([[CL:Functions:read-char]])) | ||
| + | ([[CL:Functions:list]] (read-char-no-hang) | ||
| + | (read-char-no-hang) | ||
| + | (read-char-no-hang))) <r>TEST-IT </r> | ||
| + | </blockquote> | ||
| + | |||
| + | //[[CL:Glossary:Implementation]]// A, where a //[[CL:Glossary:newline]]// is not required to terminate //[[CL:Glossary:interactive input]]// on the console. | ||
| + | |||
| + | <blockquote> | ||
| + | (test-it) | ||
| + | <o>__a__ </o> | ||
| + | <r>(#\a NIL NIL) </r> | ||
| + | </blockquote> | ||
| + | |||
| + | //[[CL:Glossary:Implementation]]// B, where a //[[CL:Glossary:newline]]// is required to terminate //[[CL:Glossary:interactive input]]// on the console, and where that //[[CL:Glossary:newline]]// remains on the input stream. | ||
| + | |||
| + | <blockquote> | ||
| + | (test-it) | ||
| + | <o>__a↵ __</o> | ||
| + | <r>(#\a #\Newline NIL) </r> | ||
| + | </blockquote> | ||
| + | |||
| + | ====Affected By==== | ||
| + | **[[CL:Variables:star-standard-input-star|*standard-input*]]**, **[[CL:Variables:star-terminal-io-star|*terminal-io*]]**. | ||
| + | |||
| + | ====Exceptional Situations==== | ||
| + | If an //[[CL:Glossary:end of file]]// occurs when //eof-error-p// is //[[CL:Glossary:true]]//, an error of type **[[CL:Types:end-of-file]]** is signaled . | ||
| + | |||
| + | ====See Also==== | ||
| + | * **[[CL:Functions:listen|Function LISTEN]]** | ||
| + | |||
| + | ====Notes==== | ||
| + | **read-char-no-hang** is exactly like **[[CL:Functions:read-char]]**, except that if it would be necessary to wait in order to get a character (as from a keyboard), **[[CL:Constant Variables:nil]]** is immediately returned without waiting. | ||
| + | |||
| + | \issue{ARGUMENTS-UNDERSPECIFIED:SPECIFY} | ||
