Add operator precedence table

doc/userdoc.org

@@ -1540,7 +1540,72 @@ they follow a few rules.
       \end{equation*}
     #+end_src
 
-*** TODO High-level types<<high-level-types>>
+**** Operator precedence and associativity
+
+To avoid confusions, the operators precedence in ~pugs~ language follow
+the same rules as in ~C++~.
+
+This is summarized in the following table, where ~a~ and ~b~ denotes two
+expressions.
+| Precedence | Operator |
+|------------+----------|
+|          1 | ~a++~      |
+|            | ~a--~      |
+|            | ~a[]~      |
+|------------+----------|
+|          2 | ~++a~      |
+|            | ~--a~      |
+|            | ~not a~    |
+|------------+----------|
+|          3 | ~a*b~      |
+|            | ~a/b~      |
+|------------+----------|
+|          4 | ~a+b~      |
+|            | ~a-b~      |
+|------------+----------|
+|          5 | ~a<<b~     |
+|            | ~a>>b~     |
+|------------+----------|
+|          6 | ~a<b~      |
+|            | ~a<=b~     |
+|            | ~a>b~      |
+|            | ~a>=b~     |
+|------------+----------|
+|          7 | ~a==b~     |
+|            | ~a!=b~     |
+|------------+----------|
+|          8 | ~a=b~      |
+|            | ~a+=b~     |
+|            | ~a-=b~     |
+|            | ~a*=b~     |
+|            | ~a/=b~     |
+
+As already said, we forbid some constructions to try to avoid spurious
+constructions. By construction associativity of many operators makes
+no sense in ~pugs~ language (affectations and increment/decrement
+operators for instance).
+
+For all other operators, the associativity rule is *left to right*. Thus
+the following code
+#+BEGIN_SRC pugs :exports source
+  - 1 + 3 - 4 + 2;
+#+END_SRC
+is equivalent to
+#+BEGIN_SRC pugs :exports source
+  (((- 1) + 3) - 4) + 2;
+#+END_SRC
+
+Obviously ~pugs~ allows the use of parenthesis to write
+expressions. It is enough to give a simple example.
+#+NAME: parenthesis-precedence
+#+BEGIN_SRC pugs :exports both :results output
+  cout << " 2 + 3  * 4 = " <<  2 + 3  * 4 << "\n";
+  cout << "(2 + 3) * 4 = " << (2 + 3) * 4 << "\n";
+#+END_SRC
+the output is
+#+RESULTS: parenthesis-precedence
+
+*** High-level types<<high-level-types>>
 
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