From 744fb9202db5a2eec0ef74835b77725c05e85ab4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20G=C3=B6m=C3=B6ri?= <gomoripeti@gmail.com>
Date: Mon, 2 Jul 2018 22:48:35 +0200
Subject: Document allowed integer ops in types

---
 system/doc/reference_manual/typespec.xml | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

(limited to 'system')

diff --git a/system/doc/reference_manual/typespec.xml b/system/doc/reference_manual/typespec.xml
index f6a19397c3..a8b7393cc8 100644
--- a/system/doc/reference_manual/typespec.xml
+++ b/system/doc/reference_manual/typespec.xml
@@ -113,8 +113,8 @@
         | Erlang_Atom           %% 'foo', 'bar', ...
 
   Bitstring :: <<>>
-             | <<_:M>>          %% M is a positive integer
-             | <<_:_*N>>        %% N is a positive integer
+             | <<_:M>>          %% M is an Integer_Value that evaluates to a positive integer
+             | <<_:_*N>>        %% N is an Integer_Value that evaluates to a positive integer
              | <<_:M, _:_*N>>
 
   Fun :: fun()                  %% any function
@@ -123,8 +123,17 @@
        | fun((TList) -> Type)
 
   Integer :: integer()
-           | Erlang_Integer                    %% ..., -1, 0, 1, ... 42 ...
-           | Erlang_Integer..Erlang_Integer    %% specifies an integer range
+           | Integer_Value
+           | Integer_Value..Integer_Value      %% specifies an integer range
+
+  Integer_Value :: Erlang_Integer              %% ..., -1, 0, 1, ... 42 ...
+                 | Erlang_Character            %% $a, $b ...
+                 | Integer_Value BinaryOp Integer_Value
+                 | UnaryOp Integer_Value
+
+  BinaryOp :: '*' | 'div' | 'rem' | 'band' | '+' | '-' | 'bor' | 'bxor' | 'bsl' | 'bsr'
+
+  UnaryOp :: '+' | '-' | 'bnot'
 
   List :: list(Type)                           %% Proper list ([]-terminated)
         | maybe_improper_list(Type1, Type2)    %% Type1=contents, Type2=termination
@@ -150,9 +159,14 @@
 
   Union :: Type1 | Type2
 ]]></pre>
+  <p>
+    Integer values are either integer or character literals or expressions
+    consisting of possibily nested unary or binary operations that evaluate to
+    an integer. Such expressions can also be used in bit strings and ranges.
+  </p>
   <p>
     The general form of bit strings is <c>&lt;&lt;_:M, _:_*N&gt;&gt;</c>,
-    where <c>M</c> and <c>N</c> are positive integers. It denotes a
+    where <c>M</c> and <c>N</c> must evaluate to positive integers. It denotes a
     bit string that is <c>M + (k*N)</c> bits long (that is, a bit string that
     starts with <c>M</c> bits and continues with <c>k</c> segments of
     <c>N</c> bits each, where <c>k</c> is also a positive integer).
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