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64 lines
1.5 KiB
Scheme
64 lines
1.5 KiB
Scheme
23 years ago
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#cs
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(module yacc-helper mzscheme
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;; General helper routines
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(provide duplicate-list? remove-duplicates overlap? vector-andmap)
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(define (vector-andmap f v)
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(let loop ((i 0))
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(cond
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((= i (vector-length v)) #t)
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(else (if (f (vector-ref v i))
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(loop (add1 i))
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#f)))))
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;; duplicate-list?: symbol list -> #f | symbol
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;; returns a symbol that exists twice in l, or false if no such symbol
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;; exists
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(define (duplicate-list? l)
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(letrec ((t (make-hash-table))
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(dl? (lambda (l)
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(cond
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((null? l) #f)
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((hash-table-get t (car l) (lambda () #f)) =>
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(lambda (x) x))
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(else
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(hash-table-put! t (car l) (car l))
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(dl? (cdr l)))))))
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(dl? l)))
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;; remove-duplicates: symbol list -> symbol list
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;; removes the duplicates from the lists
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(define (remove-duplicates sl)
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(let ((t (make-hash-table)))
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(letrec ((x
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(lambda (sl)
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(cond
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((null? sl) sl)
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((hash-table-get t (car sl) (lambda () #f))
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(x (cdr sl)))
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(else
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(hash-table-put! t (car sl) #t)
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(cons (car sl) (x (cdr sl))))))))
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(x sl))))
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;; overlap?: symbol list * symbol list -> #f | symbol
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;; Returns an symbol in l1 intersect l2, or #f is no such symbol exists
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(define (overlap? l1 l2)
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(let/ec ret
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(let ((t (make-hash-table)))
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(for-each (lambda (s1)
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(hash-table-put! t s1 s1))
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l1)
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(for-each (lambda (s2)
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(cond
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((hash-table-get t s2 (lambda () #f)) =>
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(lambda (o) (ret o)))))
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l2)
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#f)))
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)
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