106 lines
3.2 KiB
Scheme
106 lines
3.2 KiB
Scheme
;;
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;; dictionary.scm
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;;
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;; Simple dictionary implementation using assq lists.
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;;
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;; ISC License
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;;
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;; Copyright 2023 Brmlab, z.s.
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;; Dominik Pantůček <dominik.pantucek@trustica.cz>
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;;
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;; Permission to use, copy, modify, and/or distribute this software
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;; for any purpose with or without fee is hereby granted, provided
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;; that the above copyright notice and this permission notice appear
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;; in all copies.
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;;
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;; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
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;; WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
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;; WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
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;; AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
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;; CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
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;; OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
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;; NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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;; CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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;;
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(module
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dictionary
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(
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make-dict
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dict-has-key? dict-ref
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dict-remove dict-set
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dict-keys
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dictionary-tests!
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)
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(import scheme
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(chicken base)
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testing)
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;; Returns an empty dictionary represented as empty list.
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(define (make-dict)
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'())
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;; Checks whether given dictionary d contains the key k.
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(define (dict-has-key? d k)
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(if (assq k d) #t #f))
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;; Retrieves the value for key k from dictionary d. If third argument
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;; is provided it is used as default value in case the key does not
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;; exist. If only two arguments are given and the key does not exist,
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;; raises an error.
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(define (dict-ref d k . r)
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(let ((p (assq k d)))
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(if p
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(cdr p)
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(if (null? r)
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(error 'dict-ref "Key does not exist" k)
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(car r)))))
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;; Returns a new dictionary based on d with key k removed. If it
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;; doesn't contain the key, an error is raised.
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(define (dict-remove d k)
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(let loop ((s d)
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(r '())
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(e #t))
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(if (null? s)
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(if e
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(error 'dict-remove "Key does not exist" k)
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r)
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(if (eq? (caar s) k)
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(loop (cdr s) r #f)
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(loop (cdr s) (cons (car s) r) e)))))
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;; Adds a new value v under the key k to the dictionary d possibly
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;; overwriting any value which has been stored under the key
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;; before. Returns the updated dictionary.
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(define (dict-set d k v)
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(let ((dr (let loop ((s d)
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(r '()))
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(if (null? s)
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r
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(if (eq? (caar s) k)
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(loop (cdr s) r)
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(loop (cdr s) (cons (car s) r)))))))
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(cons (cons k v)
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dr)))
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;; Returns the list of keys stored in given dictionary.
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(define (dict-keys d)
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(map car d))
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;; Performs self-tests of the dictionary module.
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(define (dictionary-tests!)
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(run-tests
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dict
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(test-true make-dict (null? (make-dict)))
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(test-exn dict-ref (dict-ref (make-dict) 'nonexistent))
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(test-true dict-ref (dict-ref (make-dict) 'nonexistent #t))
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(test-equal? dict-set (dict-set (make-dict) 'nonexistent 1) '((nonexistent . 1)))
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(test-equal? dict-set (dict-set (dict-set (make-dict) 'existent 1) 'existent 2) '((existent . 2)))
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(test-exn dict-remove (dict-remove (make-dict) 'nonexistent))
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(test-true dict-remove (null? (dict-remove (dict-set (make-dict) 'existing 1) 'existing)))
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(test-equal? dict-keys (dict-keys (dict-set (make-dict) 'existing 1)) '(existing))
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))
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)
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