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43 lines
949 B
Scheme
43 lines
949 B
Scheme
27 years ago
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;; --------------------------------------------------------------------------
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;; list-library.ss
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;; export:
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;; collect:
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;; (A ((cons B (listof B)) (listof B) (union A C) -> (union A C))
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;; ->
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;; ((listof B) -> (union A C)))
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; #|
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; (unit/sig
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; (collect filter set-minus subset?)
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; (import plt:userspace^)
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; |#
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(define collect
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(lambda (base combine)
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(local ((define C
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(lambda (l)
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(cond
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((null? l) base)
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(else (combine l (car l) (C (cdr l))))))))
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C)))
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(define filter
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(lambda (p? l)
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[(collect null (lambda (_ x rest) (if (p? x) (cons x rest) rest))) l]))
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;; set library
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(define set-minus
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(lambda (set1 set2)
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[(collect null (lambda (_ e1 rest) (if (member e1 set2) rest (cons e1 rest))))
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set1]))
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(define subset?
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(lambda (state1 state2)
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(cond
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((null? state1) #t)
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(else (and (member (car state1) state2)
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(subset? (cdr state1) state2))))))
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; #|
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; )
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; |#
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