From 7ab69869d1298c899867bdf2b6f3d737d6572821 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Tue, 11 Dec 2018 22:27:03 -0800
Subject: [PATCH] optional done

---
 xenomorph/xenomorph/redo/optional.rkt         |  39 +++++++
 .../xenomorph/redo/test/optional-test.rkt     | 100 ++++++++++++++++++
 2 files changed, 139 insertions(+)
 create mode 100644 xenomorph/xenomorph/redo/optional.rkt
 create mode 100644 xenomorph/xenomorph/redo/test/optional-test.rkt

diff --git a/xenomorph/xenomorph/redo/optional.rkt b/xenomorph/xenomorph/redo/optional.rkt
new file mode 100644
index 00000000..82989430
--- /dev/null
+++ b/xenomorph/xenomorph/redo/optional.rkt
@@ -0,0 +1,39 @@
+#lang racket/base
+(require "helper.rkt")
+(provide (all-defined-out))
+
+#|
+approximates
+https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
+|#
+
+(define (resolve-condition xo parent)
+  (define maybe-proc (xoptional-condition xo))
+  (if (procedure? maybe-proc)
+      (maybe-proc parent)
+      maybe-proc))
+
+(define (xoptional-decode xo [port-arg (current-input-port)] #:parent [parent #f])
+  (define port (->input-port port-arg))
+  (when (resolve-condition xo parent)
+    (decode (xoptional-type xo) port #:parent parent)))
+
+(define (xoptional-encode xo val [port-arg (current-output-port)] #:parent [parent #f])
+  (define port (if (output-port? port-arg) port-arg (open-output-bytes)))
+  (when (resolve-condition xo parent)
+    (encode (xoptional-type xo) val port #:parent parent))
+  (unless port-arg (get-output-bytes port)))
+
+(define (xoptional-size xo [val #f] [parent #f])
+  (if (resolve-condition xo parent)
+      (size (xoptional-type xo) val parent)
+      0))
+
+(struct xoptional (type condition) #:transparent
+  #:methods gen:xenomorphic
+  [(define decode xoptional-decode)
+   (define encode xoptional-encode)
+   (define size xoptional-size)])
+
+(define (+xoptional type [condition #t])
+  (xoptional type condition))
diff --git a/xenomorph/xenomorph/redo/test/optional-test.rkt b/xenomorph/xenomorph/redo/test/optional-test.rkt
new file mode 100644
index 00000000..bd5f7503
--- /dev/null
+++ b/xenomorph/xenomorph/redo/test/optional-test.rkt
@@ -0,0 +1,100 @@
+#lang racket/base
+(require rackunit
+         "../helper.rkt"
+         "../number.rkt"
+         "../optional.rkt")
+
+#|
+approximates
+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))
+   (check-equal? (decode optional) (void))
+   (check-equal? (pos (current-input-port)) 0)))
+
+(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)))
+   (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))
+   (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))
+   (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)))
+   (check-not-equal? (decode optional) (void))
+   (check-equal? (pos (current-input-port)) 1)))
+
+(test-case
+ "size"
+ (check-equal? (size (+xoptional uint8 #f)) 0))
+
+(test-case
+ "size should return 0 when condition is a function and falsy"
+ (check-equal? (size (+xoptional uint8 (λ _ #f))) 0))
+
+(test-case
+ "size should return given type size when condition is omitted"
+ (check-equal? (size (+xoptional uint8)) 1))
+
+(test-case
+ "size should return given type size when condition is truthy"
+ (check-equal? (size (+xoptional uint8 #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))
+
+(test-case
+ "encode should not encode when condition is falsy"
+ (parameterize ([current-output-port (open-output-bytes)])
+   (define optional (+xoptional uint8 #f))
+   (encode optional 128)
+   (check-equal? (dump (current-output-port)) (bytes))))
+
+(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)))
+   (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))
+   (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))
+   (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)))
+   (encode optional 128)
+   (check-equal? (dump (current-output-port)) (bytes 128))))
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