26 lines
608 B
Common Lisp
26 lines
608 B
Common Lisp
(define (fflatten l)
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(cond
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[(null? l) null]
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[(not (list? l)) (list l)]
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[else (append (fflatten (first l)) (fflatten (rest l)))]))
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;;
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(define L' [[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []])
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(fflatten L) ;; use custom function
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→ (1 2 3 4 5 6 7 8)
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(flatten L) ;; use built-in
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→ (1 2 3 4 5 6 7 8)
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;; Remarks
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;; null is the same as () - the empty list -
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(flatten '(null null null))
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→ null
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(flatten '[ () () () ])
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→ null
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(flatten null)
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❗ error: flatten : expected list : null
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;; The 'reverse' of flatten is group
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(group '( 4 5 5 5 6 6 7 8 7 7 7 9))
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→ ((4) (5 5 5) (6 6) (7) (8) (7 7 7) (9))
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