25 lines
652 B
Scheme
25 lines
652 B
Scheme
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(define-library (picrin optional)
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(import (scheme base))
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(define-syntax optional
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(syntax-rules ()
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((_ args default)
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(let ((t args))
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(if (null? t) default (car t))))))
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(define-syntax let-optionals*
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(syntax-rules ()
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((_ args () body ...)
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(begin body ...))
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((_ args ((var default) . tail) body ...)
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(let* ((t args)
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(var (if (null? t) default (car t)))
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(remain (if (null? t) '() (cdr t))))
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(let-optionals* remain tail body ...)))
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((_ args rest body ...)
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(let ((rest args))
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body ...))))
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(export optional
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let-optionals*))
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