DOc, strings. [ci skip]

doc/tutorial/index.rst

@@ -12,6 +12,7 @@ Contents:
 
    hello 
    integers
+   strings
    pythagoras
    guiindex 
 

doc/tutorial/strings.rst

@@ -0,0 +1,94 @@
+Strings
+=======
+
+A string is basically a sequence of characters
+with a definite length.
+
+Type
+----
+
+The easiest string type to use in Felix is the one based
+on C++:
+
+.. code-block:: felix
+
+    type string = "::std::basic_string<char>"
+      requires Cxx_headers::string
+    ;
+
+Literals
+--------
+
+There are two simple forms of string literals:
+
+.. code-block:: felix
+
+    var x = "I am a string";
+    var y = 'I am a string too';
+
+using double quote delimiters and single quote delimiters.
+These literals cannot exceed a single line.  However
+you can concatenate them by juxtaposition:
+
+.. code-block:: felix
+
+    var verse = 
+      "I am the first line,\n"
+      'and I am the second.'
+    ;
+
+Notice the special encoding `\n` which inserts and end of
+line character into the string rather than a `\` followed
+by an `n`. This is called an escape.
+
+You can prevent escapes being translated with raw
+strings like this:
+
+.. code-block:: felix
+
+    r"This \n is retained as two chars"
+
+Only double quoted strings can be raw.
+
+Felix also has triple quoted strings, which span
+line boundaries, and include end of lines in the
+literal:
+
+.. code-block:: felix
+    """This is
+    a very long 
+    string"""
+
+which contains two end of line characters in the string, whilst
+this one:
+
+.. code-block:: felix
+
+    '''
+    Here is another
+    long string
+    '''
+
+has three end of lines (one after the first triple quote).
+
+Operations
+----------
+
+Strings can be concatenated with the infix `+` operator or
+just written next to each other, juxtaposition has a higher
+precedence than infix `+`.
+
+.. code-block:: felix
+
+    var x = "middle";
+    var y = "Start" x + "end";
+
+In this case, the first concatenation of x is done first,
+then the second one which appends "end". The result
+is independent of the ordering because concatenation
+is associative, the run time performance, however, is not,
+because concatenation requires coping.
+
+
+
+