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139 lines
5.0 KiB
Racket
139 lines
5.0 KiB
Racket
#lang racket/base
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(require racket/contract racket/match xml racket/list)
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(require sugar)
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;; a tagged-xexpr consists of a tag, optional attributes, and then elements.
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(define+provide/contract (xexpr-tag? x)
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(any/c . -> . boolean?)
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(symbol? x))
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(define+provide/contract (xexpr-attr? x)
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(any/c . -> . boolean?)
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(match x
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[(list (list (? symbol?) (? string?)) ...) #t]
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[else #f]))
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(define+provide/contract (xexpr-element? x)
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(any/c . -> . boolean?)
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(or (string? x) (tagged-xexpr? x) (symbol? x)
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(valid-char? x) (cdata? x)))
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(define+provide/contract (xexpr-elements? x)
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(any/c . -> . boolean?)
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(match x
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[(list elem ...) (andmap xexpr-element? elem)]
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[else #f]))
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;; is it a named x-expression?
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;; todo: rewrite this recurively so errors can be pinpointed (for debugging)
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(define+provide/contract (tagged-xexpr? x)
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(any/c . -> . boolean?)
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(and (xexpr? x) ; meets basic xexpr contract
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(match x
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[(list (? symbol? name) rest ...) ; is a list starting with a symbol
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(or (andmap xexpr-element? rest) ; the rest is content or ...
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(and (xexpr-attr? (car rest)) (andmap xexpr-element? (cdr rest))))] ; attr + content
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[else #f])))
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;; convert list of alternating keys & values to attr
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;; todo: make contract. Which is somewhat complicated:
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;; list of items, made of xexpr-attr or even numbers of symbol/string pairs
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;; use splitf*-at with xexpr-attr? as test, then check lengths of resulting lists
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(define+provide/contract (make-xexpr-attr . items)
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(() #:rest (listof (λ(i) (or (xexpr-attr? i) (symbol? i) (string? i)))) . ->* . xexpr-attr?)
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;; need this function to make sure that 'foo and "foo" are treated as the same hash key
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(define (make-attr-list items)
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(if (empty? items)
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empty
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(let ([key (->symbol (first items))]
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[value (->string (second items))]
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[rest (drop items 2)])
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(append (list key value) (make-attr-list rest)))))
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;; use flatten to splice xexpr-attrs into list
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;; use hash to ensure keys are unique (later values will overwrite earlier)
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(define attr-hash (apply hash (make-attr-list (flatten items))))
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`(,@(map (λ(k) (list k (get attr-hash k)))
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;; sort needed for predictable results for unit tests
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(sort (hash-keys attr-hash) (λ(a b) (string<? (->string a) (->string b)))))))
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;; create tagged-xexpr from parts (opposite of break-tagged-xexpr)
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(define+provide/contract (make-tagged-xexpr name [attr empty] [content empty])
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; xexpr/c provides a nicer error message,
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; but is not sufficient on its own (too permissive)
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((symbol?) (xexpr-attr? (listof xexpr-element?))
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. ->* . tagged-xexpr?)
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(filter-not empty? `(,name ,attr ,@content)))
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;; decompose tagged-xexpr into parts (opposite of make-tagged-xexpr)
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(define+provide/contract (break-tagged-xexpr x)
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(tagged-xexpr? . -> .
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(values symbol? xexpr-attr? (listof xexpr-element?)))
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(match
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; tagged-xexpr may or may not have attr
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; if not, add empty attr so that decomposition only handles one case
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(match x
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[(list _ (? xexpr-attr?) _ ...) x]
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[else `(,(car x) ,empty ,@(cdr x))])
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[(list tag attr content ...) (values tag attr content)]))
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;; convenience functions to retrieve only one part of tagged-xexpr
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(define+provide/contract (tagged-xexpr-tag x)
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(tagged-xexpr? . -> . xexpr-tag?)
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(car x))
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(define+provide/contract (tagged-xexpr-attr x)
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(tagged-xexpr? . -> . xexpr-attr?)
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(define-values (tag attr content) (break-tagged-xexpr x))
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attr)
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(define+provide/contract (tagged-xexpr-elements x)
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(tagged-xexpr? . -> . (listof xexpr-element?))
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(define-values (tag attrt elements) (break-tagged-xexpr x))
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elements)
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;; remove all attr blocks (helper function)
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(define+provide/contract (remove-attrs x)
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(tagged-xexpr? . -> . tagged-xexpr?)
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(match x
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[(? tagged-xexpr?) (let-values ([(tag attr elements) (break-tagged-xexpr x)])
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(make-tagged-xexpr tag empty (remove-attrs elements)))]
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[(? list?) (map remove-attrs x)]
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[else x]))
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(define+provide/contract (map-xexpr-elements proc x)
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(procedure? tagged-xexpr? . -> . tagged-xexpr?)
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(define-values (tag attr elements) (break-tagged-xexpr x))
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(make-tagged-xexpr tag attr (map proc elements)))
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;; function to split tag out of tagged-xexpr
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(define+provide/contract (split-tag-from-xexpr tag tx)
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(xexpr-tag? tagged-xexpr? . -> . (values (listof xexpr-element?) tagged-xexpr? ))
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(define matches '())
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(define (extract-tag x)
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(cond
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[(and (tagged-xexpr? x) (equal? tag (car x)))
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; stash matched tag but return empty value
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(begin
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(set! matches (cons x matches))
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empty)]
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[(tagged-xexpr? x) (let-values([(tag attr body) (break-tagged-xexpr x)])
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(make-tagged-xexpr tag attr (extract-tag body)))]
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[(xexpr-elements? x) (filter-not empty? (map extract-tag x))]
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[else x]))
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(define tx-extracted (extract-tag tx)) ;; do this first to fill matches
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(values (reverse matches) tx-extracted)) |