34 lines
1.5 KiB
Scheme
34 lines
1.5 KiB
Scheme
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(define format
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(lambda (format-string . objects)
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(let ((buffer (open-output-string)))
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(let loop ((format-list (string->list format-string))
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(objects objects))
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(cond ((null? format-list) (get-output-string buffer))
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((char=? (car format-list) #\~)
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(if (null? (cdr format-list))
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(error 'format "Incomplete escape sequence")
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(case (cadr format-list)
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((#\a)
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(if (null? objects)
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(error 'format "No value for escape sequence")
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(begin
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(display (car objects) buffer)
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(loop (cddr format-list) (cdr objects)))))
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((#\s)
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(if (null? objects)
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(error 'format "No value for escape sequence")
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(begin
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(write (car objects) buffer)
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(loop (cddr format-list) (cdr objects)))))
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((#\%)
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(newline buffer)
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(loop (cddr format-list) objects))
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((#\~)
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(write-char #\~ buffer)
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(loop (cddr format-list) objects))
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(else
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(error 'format "Unrecognized escape sequence")))))
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(else (write-char (car format-list) buffer)
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(loop (cdr format-list) objects)))))))
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