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txexpr/main.rkt

154 lines
5.2 KiB
Racket

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