2021-06-07 09:09:20 +00:00
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#lang racket/base
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(require racket/contract racket/list racket/match)
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(provide metadata? metadata-ref metadata-ref+)
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(define metadata?
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(listof (or/c
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(list/c 'date integer? integer? integer?)
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(list/c 'title string?)
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2021-06-10 23:45:14 +00:00
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(list/c 'lang string?)
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2021-06-08 05:20:14 +00:00
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(cons/c 'tags (listof string?))
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2021-06-07 09:09:20 +00:00
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(list/c 'summary string?)
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(cons/c 'authors (listof string?)))))
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(define (metadata-ref md key [default (λ () (error "no such key"))])
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(match (assoc key md)
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[#f (if (procedure? default) (default) default)]
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[(cons _ rst) rst]))
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(define (metadata-ref+ md key [default (λ () (error "no such key"))])
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2021-06-10 23:45:14 +00:00
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(match (assoc key md)
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[#f (if (procedure? default) (default) default)]
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[(list _ snd) snd]))
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