diff --git a/xenomorph/xenomorph/redo/buffer.rkt b/xenomorph/xenomorph/redo/buffer.rkt
index c534a9f0..c3a7c47b 100644
--- a/xenomorph/xenomorph/redo/buffer.rkt
+++ b/xenomorph/xenomorph/redo/buffer.rkt
@@ -36,5 +36,9 @@ https://github.com/mbutterick/restructure/blob/master/src/Buffer.coffee
    (define encode xbuffer-encode)
    (define size xbuffer-size)])
 
-(define (+xbuffer [len #xffff])
+(define (+xbuffer [len-arg #f]
+                  #:length [len-kwarg #f])
+  (define len (or len-arg len-kwarg #xffff))
+  (unless (length-resolvable? len)
+    (raise-argument-error '+xbuffer "resolvable length" len))
   (xbuffer len))
\ No newline at end of file
diff --git a/xenomorph/xenomorph/redo/enum.rkt b/xenomorph/xenomorph/redo/enum.rkt
index 5cab0c07..c8394638 100644
--- a/xenomorph/xenomorph/redo/enum.rkt
+++ b/xenomorph/xenomorph/redo/enum.rkt
@@ -31,5 +31,13 @@ https://github.com/mbutterick/restructure/blob/master/src/Enum.coffee
    (define encode xenum-encode)
    (define size xenum-size)])
 
-(define (+xenum type [options null])
-  (xenum type options))
\ No newline at end of file
+(define (+xenum [type-arg #f] [values-arg #f]
+                #:type [type-kwarg #f]
+                #:values [values-kwarg #f])
+  (define type (or type-arg type-kwarg))
+  (unless (xenomorphic? type)
+    (raise-argument-error '+xenum "xenomorphic type" type))
+  (define values (or values-arg values-kwarg))
+  (unless (list? values)
+    (raise-argument-error '+xenum "list of values" values))
+  (xenum type values))
\ No newline at end of file
diff --git a/xenomorph/xenomorph/redo/optional.rkt b/xenomorph/xenomorph/redo/optional.rkt
index 2ade74e5..7480a1d4 100644
--- a/xenomorph/xenomorph/redo/optional.rkt
+++ b/xenomorph/xenomorph/redo/optional.rkt
@@ -1,4 +1,4 @@
-#lang racket/base
+#lang debug racket/base
 (require "helper.rkt")
 (provide (all-defined-out))
 
@@ -28,7 +28,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
 
 (define/finalize-size (xoptional-size xo [val #f] #:parent [parent #f])
   (when (resolve-condition xo parent)
-     (size (xoptional-type xo) val #:parent parent)))
+    (size (xoptional-type xo) val #:parent parent)))
 
 (struct xoptional xbase (type condition) #:transparent
   #:methods gen:xenomorphic
@@ -36,5 +36,24 @@ https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
    (define encode xoptional-encode)
    (define size xoptional-size)])
 
-(define (+xoptional type [condition #t])
+#;(define (+xoptional [type-arg #f] [cond-arg #f]
+                      #:type [type-kwarg #f]
+                      #:condition [cond-kwarg #f])
+    (define type (or type-arg type-kwarg))
+    (unless (xenomorphic? type)
+      (raise-argument-error '+xoptional"xenomorphic type" type))
+    (define condition (or cond-arg cond-kwarg))
+    (xoptional type condition))
+
+(define no-val (gensym))
+(define (+xoptional [type-arg #f] [cond-arg no-val]
+                    #:type [type-kwarg #f]
+                    #:condition [cond-kwarg no-val])
+  (define type (or type-arg type-kwarg))
+  (unless (xenomorphic? type)
+    (raise-argument-error '+xoptional"xenomorphic type" type))
+  (define condition (cond
+                      [(and (eq? cond-arg no-val) (eq? cond-kwarg no-val)) #true]
+                      [(not (eq? cond-arg no-val)) cond-arg]
+                      [(not (eq? cond-kwarg no-val)) cond-kwarg]))
   (xoptional type condition))
diff --git a/xenomorph/xenomorph/redo/test/buffer-test.rkt b/xenomorph/xenomorph/redo/test/buffer-test.rkt
index 6f3851eb..d62a5266 100644
--- a/xenomorph/xenomorph/redo/test/buffer-test.rkt
+++ b/xenomorph/xenomorph/redo/test/buffer-test.rkt
@@ -13,14 +13,18 @@ https://github.com/mbutterick/restructure/blob/master/test/Buffer.coffee
 (test-case
  "buffer should decode"
  (parameterize ([current-input-port (open-input-bytes (bytes #xab #xff #x1f #xb6))])
-   (define buf (+xbuffer 2))
+   (define buf (+xbuffer #:length 2))
    (check-equal? (decode buf) (bytes #xab #xff))
    (check-equal? (decode buf) (bytes #x1f #xb6))))
 
+(test-case
+ "buffer should error on invalid length"
+ (check-exn exn:fail:contract? (λ () (+xbuffer #:length #true))))
+
 (test-case
  "buffer should decode with post-decode"
  (parameterize ([current-input-port (open-input-bytes (bytes #xab #xff #x1f #xb6))])
-   (define buf (+xbuffer 2))
+   (define buf (+xbuffer #:length 2))
    (set-post-decode! buf (λ (bs) (bytes 1 2)))
    (check-equal? (decode buf) (bytes 1 2))
    (check-equal? (decode buf) (bytes 1 2))))
@@ -28,17 +32,17 @@ https://github.com/mbutterick/restructure/blob/master/test/Buffer.coffee
 (test-case
  "buffer should decode with parent key length"
  (parameterize ([current-input-port (open-input-bytes (bytes #xab #xff #x1f #xb6))])
-   (define buf (+xbuffer 'len))
+   (define buf (+xbuffer #:length 'len))
    (check-equal? (decode buf #:parent (hash 'len 3)) (bytes #xab #xff #x1f))
    (check-equal? (decode buf #:parent (hash 'len 1)) (bytes #xb6))))
 
 (test-case
  "size should return size"
- (check-equal? (size (+xbuffer 2) (bytes #xab #xff)) 2))
+ (check-equal? (size (+xbuffer #:length 2) (bytes #xab #xff)) 2))
 
 (test-case
  "size should use defined length if no value given"
- (check-equal? (size (+xbuffer 10)) 10))
+ (check-equal? (size (+xbuffer #:length 10)) 10))
 
 (test-case
  "encode should encode"
@@ -57,4 +61,4 @@ https://github.com/mbutterick/restructure/blob/master/test/Buffer.coffee
 
 (test-case
  "encode should encode length before buffer"
- (check-equal? (encode (+xbuffer uint8) (bytes #xab #xff) #f) (bytes 2 #xab #xff)))
\ No newline at end of file
+ (check-equal? (encode (+xbuffer #:length uint8) (bytes #xab #xff) #f) (bytes 2 #xab #xff)))
\ No newline at end of file
diff --git a/xenomorph/xenomorph/redo/test/enum-test.rkt b/xenomorph/xenomorph/redo/test/enum-test.rkt
index fae02125..7fd73d22 100644
--- a/xenomorph/xenomorph/redo/test/enum-test.rkt
+++ b/xenomorph/xenomorph/redo/test/enum-test.rkt
@@ -10,7 +10,16 @@ approximates
 https://github.com/mbutterick/restructure/blob/master/test/Enum.coffee
 |#
 
-(define e (+xenum uint8 '("foo" "bar" "baz")))
+(define e (+xenum #:type uint8
+                  #:values '("foo" "bar" "baz")))
+
+(test-case
+ "should error with invalid type"
+ (check-exn exn:fail:contract? (λ () (+xenum 42))))
+
+(test-case
+ "should error with invalid values"
+ (check-exn exn:fail:contract? (λ () (+xenum #:values 42))))
 
 (test-case
  "should have the right size"
diff --git a/xenomorph/xenomorph/redo/test/optional-test.rkt b/xenomorph/xenomorph/redo/test/optional-test.rkt
index 5806167c..e3749772 100644
--- a/xenomorph/xenomorph/redo/test/optional-test.rkt
+++ b/xenomorph/xenomorph/redo/test/optional-test.rkt
@@ -12,14 +12,14 @@ https://github.com/mbutterick/restructure/blob/master/test/Optional.coffee
 (test-case
  "decode should not decode when condition is falsy"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8 #f))
+   (define optional (+xoptional #:type uint8 #:condition #f))
    (check-equal? (decode optional) (void))
    (check-equal? (pos (current-input-port)) 0)))
 
 (test-case
  "decode with post-decode"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8 #f))
+   (define optional (+xoptional #:type uint8 #:condition #f))
    (set-post-decode! optional (λ (val) 42))
    (check-equal? (decode optional) 42)
    (check-equal? (pos (current-input-port)) 0)))
@@ -27,62 +27,62 @@ https://github.com/mbutterick/restructure/blob/master/test/Optional.coffee
 (test-case
  "decode should not decode when condition is a function and falsy"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8 (λ _ #f)))
+   (define optional (+xoptional #:type uint8 #:condition (λ _ #f)))
    (check-equal? (decode optional) (void))
    (check-equal? (pos (current-input-port)) 0)))
 
 (test-case
  "decode should decode when condition is omitted"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8))
+   (define optional (+xoptional #:type uint8))
    (check-not-equal? (decode optional) (void))
    (check-equal? (pos (current-input-port)) 1)))
 
 (test-case
  "decode should decode when condition is truthy"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8 #t))
+   (define optional (+xoptional #:type uint8 #:condition #t))
    (check-not-equal? (decode optional) (void))
    (check-equal? (pos (current-input-port)) 1)))
 
 (test-case
  "decode should decode when condition is a function and truthy"
  (parameterize ([current-input-port (open-input-bytes (bytes 0))])
-   (define optional (+xoptional uint8 (λ _ #t)))
+   (define optional (+xoptional #:type uint8 #:condition (λ _ #t)))
    (check-not-equal? (decode optional) (void))
    (check-equal? (pos (current-input-port)) 1)))
 
 (test-case
  "size"
- (check-equal? (size (+xoptional uint8 #f)) 0))
+ (check-equal? (size (+xoptional #:type uint8 #:condition #f)) 0))
 
 (test-case
  "size should return 0 when condition is a function and falsy"
- (check-equal? (size (+xoptional uint8 (λ _ #f))) 0))
+ (check-equal? (size (+xoptional #:type uint8 #:condition (λ _ #f))) 0))
 
 (test-case
  "size should return given type size when condition is omitted"
- (check-equal? (size (+xoptional uint8)) 1))
+ (check-equal? (size (+xoptional #:type uint8)) 1))
 
 (test-case
  "size should return given type size when condition is truthy"
- (check-equal? (size (+xoptional uint8 #t)) 1))
+ (check-equal? (size (+xoptional #:type uint8 #:condition #t)) 1))
 
 (test-case
  "size should return given type size when condition is a function and truthy"
- (check-equal? (size (+xoptional uint8 (λ _ #t))) 1))
+ (check-equal? (size (+xoptional #:type uint8 #:condition (λ _ #t))) 1))
 
 (test-case
  "encode should not encode when condition is falsy"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8 #f))
+   (define optional (+xoptional #:type uint8 #:condition #f))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes))))
 
 (test-case
  "encode with pre-encode"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8))
+   (define optional (+xoptional #:type uint8))
    (set-pre-encode! optional (λ (val) 42))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes 42))))
@@ -90,27 +90,27 @@ https://github.com/mbutterick/restructure/blob/master/test/Optional.coffee
 (test-case
  "encode should not encode when condition is a function and falsy"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8 (λ _ #f)))
+   (define optional (+xoptional #:type uint8 #:condition (λ _ #f)))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes))))
 
 (test-case
  "encode should encode when condition is omitted"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8))
+   (define optional (+xoptional #:type uint8))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes 128))))
 
 (test-case
  "encode should encode when condition is truthy"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8 #t))
+   (define optional (+xoptional #:type uint8 #:condition #t))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes 128))))
 
 (test-case
  "encode should encode when condition is a function and truthy"
  (parameterize ([current-output-port (open-output-bytes)])
-   (define optional (+xoptional uint8 (λ _ #t)))
+   (define optional (+xoptional #:type uint8 #:condition (λ _ #t)))
    (encode optional 128)
    (check-equal? (dump (current-output-port)) (bytes 128))))
\ No newline at end of file