convert input to txexpr-attr-value (closes #17)

txexpr/base.rkt

@@ -240,7 +240,7 @@
 (define+provide+safe (attr-join tx key value)
   (txexpr? can-be-txexpr-attr-key? can-be-txexpr-attr-value? . -> . txexpr?)
   (define starting-values (string-split (attr-ref tx key "")))
-  (attr-set tx key (string-join (append starting-values (list value)) " ")))      
+  (attr-set tx key (string-join (append starting-values (list (->txexpr-attr-value value))) " ")))      
 
 (define no-failure-result (gensym)) ; failure-result might be #false
 (define+provide+safe (attr-ref attrs-arg key [failure-result no-failure-result])

txexpr/test/tests.rkt

@@ -233,6 +233,8 @@
                (and (member '(foo "fraw") (get-attrs result))
                     (member '(zim "zam") (get-attrs result)) #t)))
  (check-txexprs-equal? (attr-join '(p ((foo "bar"))) 'foo "zam") '(p ((foo "bar zam"))))
+ (check-txexprs-equal? (attr-join '(tx ((foo "bar")) baz (p bin)) 'key 'val)
+                       '(tx ((foo "bar") (key "val")) baz (p bin)))
  (check-true (let ([result (attr-join '(p ((foo "bar"))) 'zim "zam")])
                (and (member '(foo "bar") (get-attrs result))
                     (member '(zim "zam") (get-attrs result)) #t)))