[210_10] 实现 bag 构造器、访问器与谓词 #391
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jetjinser
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Jan 29, 2026
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jetjinser
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后面的还没看，先改成用 hash-table 存 entry 吧
goldfish/srfi/srfi-113.scm
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| (comparator bag-element-comparator)) | ||
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| (define (check-bag obj) | ||
| (if (not (bag? obj)) (type-error "not a bag" obj))) |
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Suggested change
| (if (not (bag? obj)) (type-error "not a bag" obj))) | |
| (when (not (bag? obj)) (type-error "not a bag" obj))) |
goldfish/srfi/srfi-113.scm
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| (define (bag-entry element count) | ||
| (cons element count)) | ||
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| (define (bag-entry-element entry) | ||
| (car entry)) | ||
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| (define (bag-entry-count entry) | ||
| (cdr entry)) |
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bag-entry 如果需要这些 proc 的话，也用 record，不要这么写，这里相当于手动构造 record 了。
但是没必要另外构造这个，entries 用一个 hash-table 就行。
另外如果这么写，也写得复杂了一些
Suggested change
| (define (bag-entry element count) | |
| (cons element count)) | |
| (define (bag-entry-element entry) | |
| (car entry)) | |
| (define (bag-entry-count entry) | |
| (cdr entry)) | |
| (define (bag-entry element count) | |
| (cons element count)) | |
| (define bag-entry-element car) | |
| (define bag-entry-count cdr) |
goldfish/srfi/srfi-113.scm
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| (if (not (and (exact-integer? count) (>= count 0))) | ||
| (type-error "bag-increment!" count)) |
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Suggested change
| (if (not (and (exact-integer? count) (>= count 0))) | |
| (type-error "bag-increment!" count)) | |
| (unless (and (exact-integer? count) (>= count 0)) | |
| (type-error "bag-increment!" count)) |
goldfish/srfi/srfi-113.scm
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| (%make-bag entries comparator) | ||
| bag? | ||
| (entries bag-entries set-bag-entries!) | ||
| (comparator bag-element-comparator)) |
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Suggested change
| (comparator bag-element-comparator)) | |
| (comparator bag-comparator)) |
保持简单些吧，不然有可能会带来 bag-element 的 comparator field 的混淆。
goldfish/srfi/srfi-113.scm
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| (let* ((eq (comparator-equality-predicate (bag-element-comparator bag))) | ||
| (entries (bag-entries bag))) | ||
| (let loop ((rest entries)) | ||
| (cond | ||
| ((null? rest) | ||
| (set-bag-entries! bag (cons (bag-entry element count) entries))) | ||
| (else | ||
| (let ((entry (car rest))) | ||
| (if (eq (bag-entry-element entry) element) | ||
| (set-cdr! entry (+ count (bag-entry-count entry))) | ||
| (loop (cdr rest))))))) |
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因为 entries 是个 alist，可以用 assq 实现，但更好的方式还是 hash-table-xxx 的操作
goldfish/srfi/srfi-113.scm
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| (define (bag-decrement! bag element count) | ||
| (check-bag bag) | ||
| (if (not (and (exact-integer? count) (>= count 0))) | ||
| (type-error "bag-decrement!" count)) | ||
| (if (= count 0) | ||
| bag | ||
| (let* ((eq (comparator-equality-predicate (bag-element-comparator bag))) | ||
| (entries (bag-entries bag))) | ||
| (let loop ((prev #f) (rest entries)) | ||
| (cond | ||
| ((null? rest) bag) | ||
| (else | ||
| (let ((entry (car rest))) | ||
| (if (eq (bag-entry-element entry) element) | ||
| (let ((new-count (- (bag-entry-count entry) count))) | ||
| (if (> new-count 0) | ||
| (set-cdr! entry new-count) | ||
| (if prev | ||
| (set-cdr! prev (cdr rest)) | ||
| (set-bag-entries! bag (cdr rest)))) | ||
| bag) | ||
| (loop entry (cdr rest)))))))))) |
jetjinser
requested changes
Jan 29, 2026
goldfish/srfi/srfi-113.scm
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| (define (bag-entry-count entry) | ||
| entry) |
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这个没有意义，let 的时候命名清楚 entry-count 就行
goldfish/srfi/srfi-113.scm
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| (when (> entry 0) | ||
| (let ((new-count (- (bag-entry-count entry) count))) | ||
| (if (> new-count 0) | ||
| (hash-table-set! entries element new-count) | ||
| (hash-table-delete! entries element)))) |
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直接判断 entry > count 就行了吧
tests/goldfish/liii/bag-test.scm
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| (check-true (not (not (member 1 b-list)))) | ||
| (check-true (not (not (member 2 b-list)))) |
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两次 not 没有意义
list 直接 check 内容吧
jetjinser
approved these changes
Jan 29, 2026
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| (check-false (not (member 1 b-list))) | ||
| (check-false (not (member 2 b-list))) |
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(check-true (member 1 b-list))
(check-true (member 2 b-list))
想到确实不能直接检查 b-list 内容，因为 bag 不保证顺序，这么检查是对的。
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