change _length key name

xenomorph/xenomorph/array.rkt

@@ -30,7 +30,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Array.coffee
                              (mhasheq 'parent parent
                                       x:start-offset-key (pos port)
                                       x:current-offset-key 0
-                                      '_length @len)
+                                      x:length-key @len)
                              parent))
       (define len (resolve-length @len port parent))
       (cond
@@ -39,8 +39,8 @@ https://github.com/mbutterick/restructure/blob/master/src/Array.coffee
                            ;; resolved-len is byte length
                            [len (+ (pos port) len)]
                            ;; no resolved-len, but parent has length
-                           [(and parent (not (zero? (dict-ref parent '_length))))
-                            (+ (dict-ref parent x:start-offset-key) (dict-ref parent '_length))]
+                           [(and parent (not (zero? (dict-ref parent x:length-key))))
+                            (+ (dict-ref parent x:start-offset-key) (dict-ref parent x:length-key))]
                            ;; no resolved-len or parent, so consume whole stream
                            [else +inf.0]))
          (for/list ([i (in-naturals)]

xenomorph/xenomorph/helper.rkt

@@ -9,8 +9,9 @@
 (define x:version-key 'x:version)
 (define x:start-offset-key 'x:start-offset)
 (define x:current-offset-key 'x:current-offset)
+(define x:length-key 'x:length)
 
-(define private-keys (list 'parent x:start-offset-key x:current-offset-key '_length))
+(define private-keys (list 'parent x:start-offset-key x:current-offset-key x:length-key))
 
 (define (dict-ref* d . keys)
   (for/fold ([d d])

xenomorph/xenomorph/lazy-array.rkt

@@ -20,7 +20,7 @@ https://github.com/mbutterick/restructure/blob/master/src/LazyArray.coffee
                              (mhasheq 'parent parent
                                       x:start-offset-key starting-pos
                                       x:current-offset-key 0
-                                      '_length @len)
+                                      x:length-key @len)
                              parent))
       (define stream-starting-pos (pos port))
       (begin0

xenomorph/xenomorph/struct.rkt

@@ -19,7 +19,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
               'parent parent
               x:start-offset-key (pos port)
               x:current-offset-key 0
-              '_length len)
+              x:length-key len)
   mheq)
 
 (define (xstruct-parse-fields port sdr fields-arg)

xenomorph/xenomorph/test/array-test.rkt

@@ -62,12 +62,12 @@ https://github.com/mbutterick/restructure/blob/master/test/Array.coffee
 (test-case 
  "array: decode to the end of parent if no length given"
  (parameterize ([current-input-port (open-input-bytes (bytes 1 2 3 4 5))])
-   (check-equal? (decode (x:array #:type uint8) (current-input-port) #:parent (mhash '_length 4 x:start-offset-key 0)) '(1 2 3 4))))
+   (check-equal? (decode (x:array #:type uint8) (current-input-port) #:parent (mhash x:length-key 4 x:start-offset-key 0)) '(1 2 3 4))))
 
 (test-case 
  "array: decode to the end of the stream if parent exists, but its length is 0"
  (parameterize ([current-input-port (open-input-bytes (bytes 1 2 3 4 5))])
-   (check-equal? (decode (x:array #:type uint8) (current-input-port) #:parent (mhash '_length 0 x:start-offset-key 0)) '(1 2 3 4 5))))
+   (check-equal? (decode (x:array #:type uint8) (current-input-port) #:parent (mhash x:length-key 0 x:start-offset-key 0)) '(1 2 3 4 5))))
 
 (test-case 
  "array: decode to the end of the stream if no parent and length is given"