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@ -42,14 +42,15 @@
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(λ (ak _) (pred ak)) ; 1 arity implies key-only test
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pred)]
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[other (raise-argument-error 'do-attr-iteration "key predicate" other)]))
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(define no-value-signal (gensym))
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(for-each-attrs qs
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(λ (attrs parent-attrs)
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;; we don't iterate with `in-hash` (or `in-hash-keys`) because
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;; `attrs` might get mutated during the loop,
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;; which invalidates the reference `in-hash` is using
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(for* ([ak (in-list (hash-keys attrs))]
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[av (in-value (hash-ref attrs ak))]
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#:when (attr-predicate ak av))
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[av (in-value (hash-ref attrs ak no-value-signal))]
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#:when (and (not (eq? av no-value-signal)) (attr-predicate ak av)))
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(match (if wants-parent-attrs?
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(attr-proc ak av attrs parent-attrs)
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(attr-proc ak av attrs))
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