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Add Into (Optional :a) (List :a) instance. #998

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Add Into (Optional :a) (List :a) instance. #998

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6 changes: 6 additions & 0 deletions library/list.lisp
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Original file line number Diff line number Diff line change
Expand Up @@ -757,6 +757,12 @@ This function is equivalent to all size-N elements of `(COMBS L)`."
(cl:setf current top)))
:finally (cl:return top)))))

(define-instance (Into (Optional :a) (List :a))
(define (into opt)
(match opt
((None) Nil)
((Some a) (Cons a Nil)))))

(define-instance (Default (List :a))
(define (default) Nil)))

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