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113 lines
3.5 KiB
Scheme
113 lines
3.5 KiB
Scheme
(module util mzscheme
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(require (lib "list.ss"))
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(provide (all-defined))
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(define-struct lex-abbrev (abbrev))
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(define-struct lex-trans (f))
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#;(define-syntax test-block
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(syntax-rules ()
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((_ defs (code right-ans) ...)
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(let* defs
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(let ((real-ans code))
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(unless (equal? real-ans right-ans)
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(printf "Test failed: ~e gave ~e. Expected ~e~n"
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'code real-ans 'right-ans))) ...))))
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(define-syntax test-block
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(syntax-rules ()
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((_ x ...) (void))))
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;; A cache is (X ( -> Y) -> Y)
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;; make-cache : -> cache
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;; table map Xs to Ys. If key is mapped, its value is returned.
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;; Otherwise, build is invoked and its result is placed in the table and
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;; returned.
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;; Xs are compared with equal?
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(define (make-cache)
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(let ((table (make-hash-table 'equal)))
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(lambda (key build)
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(hash-table-get table key
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(lambda ()
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(let ((new (build)))
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(hash-table-put! table key new)
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new))))))
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(test-block ((cache (make-cache)))
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((cache '(1 2) (lambda () 9)) 9)
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((cache '(2 1) (lambda () 8)) 8)
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((cache '(1 2) (lambda () 1)) 9))
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;; make-counter : -> -> nat
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;; makes a function that returns a higher number by 1, each time
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;; it is called.
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(define (make-counter)
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(let ((counter 0))
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(lambda ()
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(begin0
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counter
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(set! counter (add1 counter))))))
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(test-block ((c (make-counter))
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(d (make-counter)))
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((c) 0)
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((d) 0)
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((c) 1)
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((d) 1)
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((c) 2))
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;; remove-dups : (list-of X) (X -> number) -> (list-of X)
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;; removes the entries from l that have the same index as a
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;; previous entry. l must be grouped by indexes.
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(define (remove-dups l index acc)
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(cond
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((null? l) (reverse acc))
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((null? acc) (remove-dups (cdr l) index (cons (car l) acc)))
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((= (index (car acc)) (index (car l)))
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(remove-dups (cdr l) index acc))
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(else
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(remove-dups (cdr l) index (cons (car l) acc)))))
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(test-block ()
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((remove-dups '((1 2) (2 2) (1 3) (1 4) (100 4) (0 5)) cadr null)
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'((1 2) (1 3) (1 4) (0 5)))
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((remove-dups null error null) null))
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;; do-simple-equiv : (list-of X) (X -> nat) -> (list-of X)
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;; Sorts l according to index and removes the entries with duplicate
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;; indexes.
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(define (do-simple-equiv l index)
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(let ((ordered (mergesort l (lambda (a b) (< (index a) (index b))))))
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(remove-dups ordered index null)))
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(test-block ()
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((do-simple-equiv '((2 2) (1 4) (1 2) (100 4) (1 3) (0 5)) cadr)
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'((2 2) (1 3) (1 4) (0 5)))
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((do-simple-equiv null error) null))
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;; replace : (list-of X) (X -> bool) (X -> (list-of X)) (list-of X) ->
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;; (list-of X)
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;; If (pred? r) for some r in l, splice (get r) in place of r in the resulting
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;; list.
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(define (replace l pred? get acc)
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(cond
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((null? l) acc)
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((pred? (car l)) (replace (cdr l) pred? get (append (get (car l)) acc)))
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(else (replace (cdr l) pred? get (cons (car l) acc)))))
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(test-block ()
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((replace null void (lambda () (list 1)) null) null)
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((replace '(1 2 3 4 3 5)
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(lambda (x) (= x 3))
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(lambda (x) (list 1 2 3))
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null)
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'(5 1 2 3 4 1 2 3 2 1)))
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)
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