add `attr-ref*`

main.rkt

@@ -1,6 +1,6 @@
 #lang racket/base
 (require (for-syntax racket/base))
-(require racket/match xml racket/string)
+(require racket/match xml racket/string racket/list racket/bool)
 
 (module+ safe (require racket/contract))
 
@@ -166,12 +166,6 @@
   (any/c . -> . boolean?)
   (ormap (λ(test) (test x)) (list txexpr-attr? txexpr-attrs? can-be-txexpr-attr-key? can-be-txexpr-attr-value?)))
 
-(define (flatten orig-sexp)
-  (let loop ([sexp orig-sexp] [acc null])
-    (cond [(null? sexp) acc]
-          [(pair? sexp) (loop (car sexp) (loop (cdr sexp) acc))]
-          [else (cons sexp acc)])))
-
 (define+provide+safe (attrs->hash . items)
   (() #:rest (listof can-be-txexpr-attrs?) . ->* . hash?)
   ;; can be liberal with input because they're all just nested key/value pairs
@@ -215,6 +209,15 @@
   (with-handlers ([exn:fail? (λ(e) (error (format "attr-ref: no value found for key ~v" key)))])
     (hash-ref (attrs->hash (get-attrs tx)) key)))
 
+(define+provide+safe (attr-ref* tx key)
+  (txexpr? can-be-txexpr-attr-key? . -> . (listof txexpr-attr-value?))
+  (filter-not false? 
+              (flatten 
+               (let loop ([tx tx])
+                 (and (txexpr? tx)
+                      (cons (and (attrs-have-key? tx key)(attr-ref tx key)) 
+                            (map loop (get-elements tx))))))))
+
 ;; convert list of alternating keys & values to attr
 (define+provide+safe (merge-attrs . items)
   (() #:rest (listof can-be-txexpr-attrs?) . ->* . txexpr-attrs?)

scribblings/txexpr.scrbl

@@ -343,6 +343,19 @@ Given a @racket[_key], look up the corresponding @racket[_value] in the attribut
 (attr-ref tx 'nonexistent-key)
 ]
 
+@defproc[
+(attr-ref*
+[tx txexpr?]
+[key can-be-txexpr-attr-key?])
+(listof txexpr-attr-value?)]
+Like @racket[attr-ref], but returns a recursively gathered list of all the @racket[_value]s for that key within @racket[_tx]. Asking for a nonexistent key produces @racket[null].
+
+@examples[#:eval my-eval
+(define tx '(div [[class "red"]] "Hello" (em ([class "blue"]) "world")))
+(attr-ref* tx 'class)
+(attr-ref* tx 'nonexistent-key)
+]
+
 
 @defproc[
 (attr-set

tests.rkt

@@ -137,6 +137,12 @@
               '(p "boing" "boing" (em "boing")))
 
 
+(check-equal? (attr-ref* '(root ((foo "bar")) "hello" "world" (meta ((foo "zam")) "bar2") 
+                  (em ((foo "zam")) "goodnight" "moon")) 'foo) '("bar" "zam" "zam"))
+
+(check-equal? (attr-ref* '(root ((foo "bar")) "hello" "world" (meta ((foo "zam")) "bar2") 
+                  (em ((foo "zam")) "goodnight" "moon")) 'nonexistent-key) '())
+
 
 (define split-this-tx '(root (meta "foo" "bar") "hello" "world" (meta "foo2" "bar2") 
                   (em "goodnight" "moon" (meta "foo3" "bar3"))))