[PATCH 02/12] doc/learn-poke-in-y-minutes.pk: Update

[Mohammad-Reza Nabipoor]

2021-05-22  Mohammad-Reza Nabipoor  <mnabipoor@gnu.org>

        * doc/learn-poke-in-y-minutes.pk (Struct Field Initializers): Update
        the example according to the recent change in behavior of field
        initializers.
---
 ChangeLog                               |  6 ++++
 doc/learn-poke-language-in-y-minutes.pk | 45 ++++++++++++++-----------
 2 files changed, 31 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index dff3e282..d62dd68c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2021-05-22  Mohammad-Reza Nabipoor  <mnabipoor@gnu.org>
+
+       * doc/learn-poke-in-y-minutes.pk (Struct Field Initializers): Update
+       the example according to the recent change in behavior of field
+       initializers.
+
 2021-05-21  Mohammad-Reza Nabipoor  <mnabipoor@gnu.org>
 
        * AUTHORS: Change my email address to gnu account.
diff --git a/doc/learn-poke-language-in-y-minutes.pk 
b/doc/learn-poke-language-in-y-minutes.pk
index c72a78e7..738319d4 100644
--- a/doc/learn-poke-language-in-y-minutes.pk
+++ b/doc/learn-poke-language-in-y-minutes.pk
@@ -455,6 +455,27 @@ var packet_size     = 1#Packet / 1#B;    /* 10 */
 var two_packet_size = 2 #Packet/#B;      /* 20 */
 
 
+/* Struct Field Initializers
+ *
+ * Initialize the field to an expression.
+ */
+type HeaderWithInit =
+  struct
+  {
+    uint<8> magic = 100UB;
+    uint<8> version = 3;
+
+    offset<uint<32>,B> data_length;
+    uint<8>[data_length] data;
+  };
+
+var hdrauto = HeaderWithInit {};
+/* hdrauto.magic == 100UB && hdrauto.version == 3UB */
+
+/* It is possible to change the value of initialized fields: */
+hdrauto.magic = 200UB;
+
+
 /* Struct Field Constraints
  *
  * It is common for struct fields to be constrained to their values to
@@ -485,27 +506,10 @@ var hdrmagic =
     magic = 100UB,
   };
 
-/* There is another way to specify the constraints: field initializers  */
-
-/* Struct Field Initializers
- *
- * Field initializer has two roles:
- *   - Introduce constraint of the form: `field == initializer_expression`
- *   - Initialize the field with initializer expression
+/* The following statement will raise an exception, because it violates
+ * the field constraint.
  */
-type HeaderWithInit =
-  struct
-  {
-    uint<8> magic = 100UB;
-    uint<8> version = 3;
-
-    offset<uint<32>,B> data_length;
-    uint<8>[data_length] data;
-  };
-
-/* With field initializers, this is possible: */
-var hdrauto = HeaderWithInit {};
-/* hdrauto.magic == 100UB && hdrauto.version == 3UB */
+/* hdrmagic.magic = 200UB; */
 
 /* It is also possible to specify both a constraint and an initializer in
  * the same field.
@@ -518,6 +522,7 @@ type HeaderMagicVersion =
   };
 var hdrmagver = HeaderMagicVersion {};
 /* hdrmagver.magic == 0x55UB && hdrmagver.version == 0x2UB */
+hdrmagver.magic = 0xaaUB;
 
 
 /* Integral Structs
-- 
2.31.1