bitfield examples & error check

xenomorph/xenomorph/bitfield.rkt

@@ -35,6 +35,12 @@ https://github.com/mbutterick/restructure/blob/master/src/Bitfield.coffee
       flag-hash)
 
     (define/augment (x:encode flag-hash port [parent #f])
+      (define invalid-flags
+        (for/list ([flag (in-hash-keys flag-hash)]
+                   #:unless (member flag @flags))
+          flag))
+      (unless (null? invalid-flags)
+        (raise-argument-error 'encode (format "valid flag name ~v" @flags) invalid-flags))
       (define bit-int (for/sum ([(flag idx) (in-indexed @flags)]
                                 #:when (and flag (hash-ref flag-hash flag #f)))
                                (arithmetic-shift 1 idx)))

xenomorph/xenomorph/scribblings/xenomorph.scrbl

@@ -1486,7 +1486,8 @@ Generate an instance of @racket[x:pointer%] (or a subclass of @racket[x:pointer%
 @defthing[x:pointer-type-key symbol? #:value 'x:ptr-type]
 @defthing[x:length-key symbol? #:value 'x:length]
 @defthing[x:val-key symbol? #:value 'x:val])]{
-Housekeeping.
+
+Private fields used for pointer housekeeping. There is no reason to mess with these.
 }
 
 
@@ -1558,6 +1559,17 @@ Generate an instance of @racket[x:bitfield%] (or a subclass of @racket[x:bitfiel
 @racket[pre-encode-proc] and @racket[post-decode-proc] control the pre-encoding and post-decoding procedures, respectively. Each takes as input the value to be processed and returns a new value.
 
 @racket[base-class] controls the class used for instantiation of the new object.   
+
+@examples[#:eval my-eval
+(define flags (x:bitfield uint8 '(alpha bravo charlie delta echo)))
+(define vals (hasheq
+              'alpha #true
+              'charlie #true
+              'echo #true))
+(encode flags vals #f)
+(decode flags #"\25")
+]
+
 }