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pollen/pollen/private/splice.rkt

69 lines
2.5 KiB
Racket

#lang racket/base
(require racket/match
racket/list)
(provide (all-defined-out))
;; (string->symbol (format "~a" #\u200B))
(define splice-signal-tag '@)
(define (attrs? x)
(match x
[(list (list (? symbol?) (? string?)) ...) #true]
[_ #false]))
(define (null-string? x) (equal? x ""))
(define ((spliceable? splicing-tag) x)
(match x
[(cons (== splicing-tag eq?) _) #true]
[_ #false]))
(define (splice x [splicing-tag splice-signal-tag])
; (listof txexpr-elements?) . -> . (listof txexpr-elements?))
(let loop ([x x])
(if (list? x) ; don't exclude `attrs?` here, because it will exclude valid splice input like '((@ "foo"))
(append-map (λ (x)
; drop the splice-signal from front with `rest`
; don't recur on attributes, so null strings are not spliced within
(define proc (if ((spliceable? splicing-tag) x) rest list))
(proc (if (attrs? x) x (loop x))))
(filter-not null-string? x))
x)))
(module+ test
(require rackunit)
(check-equal? (splice `((div 1 (,splice-signal-tag 2 "" (,splice-signal-tag 3 (div 4 (,splice-signal-tag 5))) 6) "" 7)))
'((div 1 2 3 (div 4 5) 6 7)))
(check-equal? (splice `((,splice-signal-tag 1 (,splice-signal-tag 2 "" (,splice-signal-tag 3 (div 4 (,splice-signal-tag 5))) 6) "" 7)))
'(1 2 3 (div 4 5) 6 7))
(check-equal? (splice `((,splice-signal-tag "foo" "" "bar"))) '("foo" "bar"))
(check-equal? (splice null) null)
(check-equal? (splice '(a ((href "")(foo "bar")) "zam")) '(a ((href "")(foo "bar")) "zam"))
(check-equal? (splice `((,splice-signal-tag "str"))) '("str")))
;; this will strip all empty lists.
;; in practice, they would only appear in attrs position
(define (strip-empty-attrs x)
(let loop ([x x])
(if (pair? x)
(map loop (filter-not null? x))
x)))
(module+ test
(check-equal? (strip-empty-attrs '(p ())) '(p))
(check-equal? (strip-empty-attrs '(p () "foo")) '(p "foo"))
(check-equal? (strip-empty-attrs '(p () (em () "foo") "bar")) '(p (em "foo") "bar")))
;; used with pollen/markup to suppress void arguments,
;; consistent with how pollen/pre and pollen/markdown handle them
(define (remove-voids x)
(let loop ([x x])
(if (pair? x)
(map loop (filter-not void? x))
x)))
(module+ test
(check-equal? (remove-voids (list 1 2 3 (void))) '(1 2 3))
(check-equal? (remove-voids (list 1 (void) 2 3 (list 4 5 6 (void)))) '(1 2 3 (4 5 6)))
(check-equal? (remove-voids (void)) (void)))