[/==============================================================================
    Copyright (C) 2001-2011 Joel de Guzman
    Copyright (C) 2001-2011 Hartmut Kaiser

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
===============================================================================/]

[section:string String Generators]

This module includes different string oriented generators allowing to output
character sequences. It includes the `symbols` generator and variants of the 
`string` generator.

[heading Module Header]

    // forwards to <boost/spirit/home/karma/string.hpp>
    #include <boost/spirit/include/karma_string.hpp>

Also, see __include_structure__.

[section:string String Generators (`string`, `lit`)]

[heading Description]

The string generators described in this section are:

The `string` generator emits a string of characters. The `string` generator
is implicitly verbatim: the `delimit` parser is not applied in between
characters of the string. The `string` generator has an associated
__karma_char_encoding_namespace__. This is needed when doing basic operations
such as forcing lower or upper case. Examples:

    string("Hello")
    string(L"Hello")
    string(s)         // s is a std::string

`lit`, like `string`, also emits a string of characters. The main
difference is that `lit` does not consumes an attribute. A plain
string like `"hello"` or a `std::basic_string` is equivalent to a `lit`.
Examples:

    "Hello"
    lit("Hello")
    lit(L"Hello")
    lit(s)            // s is a std::string

[heading Header]

    // forwards to <boost/spirit/home/karma/string/lit.hpp>
    #include <boost/spirit/include/karma_string.hpp>

Also, see __include_structure__.

[heading Namespace]

[table
    [[Name]]
    [[`boost::spirit::lit // alias: boost::spirit::karma::lit`]]
    [[`ns::string`]]
]

In the table above, `ns` represents a __karma_char_encoding_namespace__ used by the 
corresponding string generator. 

[heading Model of]

[:__primitive_generator_concept__]

[variablelist Notation
    [[`s`]        [Character-class specific string (See __char_class_types__),
                   or a __karma_lazy_argument__ that evaluates to a 
                   character-class specific string value]]
    [[`S`]        [The type of a character-class specific string `s`.]]
    [[`ns`]       [A __karma_char_encoding_namespace__.]]]

[heading Expression Semantics]

Semantics of an expression is defined only where it differs from, or is
not defined in __primitive_generator_concept__.

[table
    [[Expression]           [Description]]
    [[`s`]                  [Generate the string literal `s`. This generator 
                             never fails (unless the underlying output stream 
                             reports an error).]]
    [[`lit(s)`]             [Generate the string literal `s`. This generator 
                             never fails (unless the underlying output stream 
                             reports an error).]]
    [[`ns::string`]         [Generate the string provided by a mandatory 
                             attribute interpreted in the character set defined 
                             by `ns`. This generator never fails (unless the 
                             underlying output stream reports an error).]]
    [[`ns::string(s)`]      [Generate the string `s` as provided by the 
                             immediate literal value the generator is initialized 
                             from. If this generator has an associated attribute 
                             it succeeds only if the attribute is equal 
                             to the immediate literal (unless the underlying 
                             output stream reports an error). Otherwise this 
                             generator fails and does not generate any output.]]
]

[note   The generators `lit(s)` and `string(s)` can be initialized either 
        using a string literal value (i.e. `"abc"`), or using a 
        `std::basic_string<char_type, ...>`, where `char_type` is the required
        value type of the underlying character sequence.]

[caution The generator `string(s)` up to version 2.4.1 of Spirit has an 
         undocumented feature. Given argument `s` generator succeeds as long as 
         `s` is a prefix of given attribute. This problem has been fixed in 
         Spirit V2.4.2.]

[heading Attributes]

[table
    [[Expression]           [Attribute]]
    [[`s`]                  [__unused__]]
    [[`lit(s)`]             [__unused__]]
    [[`ns::string`]         [`S`, attribute is mandatory (otherwise compilation 
                             will fail)]]
    [[`ns::string(s)`]      [`S`, attribute is optional, if it is supplied, the 
                             generator compares the attribute with `s` and 
                             succeeds only if both are equal, failing otherwise]]
]

[note  In addition to their usual attribute of type `S` all listed generators 
       accept an instance of a `boost::optional<S>` as well. If the 
       `boost::optional<>` is initialized (holds a value) the generators behave 
       as if their attribute was an instance of `S` and emit the value stored
       in the `boost::optional<>`. Otherwise the generators will fail.]

[heading Complexity]

[:O(N), where N is the number of characters emitted by the string generator]

[heading Example]

[note The test harness for the example(s) below is presented in the
      __karma_basics_examples__ section.]

Some includes:

[reference_karma_includes]

Some using declarations:

[reference_karma_using_declarations_string]

Basic usage of `string` generators:

[reference_karma_string]

[endsect]

[/------------------------------------------------------------------------------]
[section:symbols Symbols Generator (`symbols`)]

[heading Description]

The class `symbols` implements an 'inverse' symbol table: an associative 
container (or map) of key-value pairs where the values are (most of the time) 
strings. It maps the value to be generated (the key) to any other value which 
will be emitted instead of the original key.

The Karma symbol table class `symbols` is-a generator, an instance of which may
be used anywhere in the grammar specification. It is an example of a
dynamic generator. A dynamic generator is characterized by its ability to
modify its behavior at run time. Initially, an empty symbols object
will emit nothing. At any time, symbols may be added, thus, dynamically
altering its behavior.

[heading Header]

    // forwards to <boost/spirit/home/karma/string/symbols.hpp>
    #include <boost/spirit/include/karma_symbols.hpp>

Also, see __include_structure__.

[heading Namespace]

[table
    [[Name]]
    [[`boost::spirit::karma::symbols`]]
]

[heading Synopsis]

    template <typename Attrib, typename T, typename Lookup
      , typename CharEncoding, typename Tag>
    struct symbols;

[heading Template parameters]

[table
    [[Parameter]        [Description]               [Default]]
    [[`Attrib`]         [The type of the original attribute to be used as 
                        the key into the symbol generator (the symbol).]  [`char`]]
    [[`T`]              [The data type associated
                        with each key.]             [__unused_type__]]
    [[`Lookup`]         [The symbol search implementation] 
                                                    [if T is `unused_type`, `std::set<Attrib>`,
                                                    and `std::map<Attrib, T>` otherwise]]
    [[`CharEncoding`]   [Used for character set selection, normally not 
                         used by end user.]         [__unused_type__]]
    [[`Tag`]            [Used for character set selection, normally not 
                         used by end user.]         [__unused_type__]]
]

[heading Model of]

[:__primitive_generator_concept__]

[variablelist Notation
    [[`Sym`]        [A `symbols` type.]]
    [[`Attrib`]     [An attribute type.]]
    [[`T`]          [A data type.]]
    [[`sym`, `sym2`][`symbols` objects.]]
    [[`sseq`]       [An __stl__ container of strings.]]
    [[`dseq`]       [An __stl__ container of data with `value_type` `T`.]]
    [[`s1`...`sN`]  [A __string__.]]
    [[`d1`...`dN`]  [Objects of type `T`.]]
    [[`f`]          [A callable function or function object.]]
    [[`f`, `l`]     [`ForwardIterator` first/last pair.]]
]

[heading Expression Semantics]

Semantics of an expression is defined only where it differs from, or is not
defined in __primitive_generator_concept__.

[table
    [[Expression]                   [Semantics]]
    [[`Sym()`]                      [Construct an empty symbols object instance named `"symbols"`.]]
    [[`Sym(name)`]                  [Construct an empty symbols object instance named `name`.]]
    [[`Sym(sym2)`]                  [Copy construct a symbols from `sym2` (Another `symbols` object).]]
    [[`Sym(sseq)`]                  [Construct symbols from `sseq` (An __stl__ container of 
                                    symbols of type `Attrib`) named `"symbols"`.]]
    [[`Sym(sseq, name)`]            [Construct symbols from `sseq` (an __stl__ container of 
                                    symbols of type `Attrib`) named `name`.]]
    [[`Sym(sseq, dseq)`]            [Construct symbols from `sseq` and `dseq`
                                    (An __stl__ container of symbols of type `Attrib` and an 
                                    __stl__ container of data with `value_type` `T`)
                                    which is named `"symbols"`.]]
    [[`Sym(sseq, dseq, name)`]      [Construct symbols from `sseq` and `dseq`
                                    (An __stl__ container of symbols of type `Attrib` and an 
                                    __stl__ container of data with `value_type` `T`)
                                    which is named `name`.]]
    [[`sym = sym2`]                 [Assign `sym2` to `sym`.]]
    [[`sym = s1, s2, ..., sN`]      [Assign one or more symbols (`s1`...`sN`) to `sym`. The 
                                     associated data values of type `T` are default constructed.]]
    [[`sym += s1, s2, ..., sN`]     [Add one or more symbols (`s1`...`sN`) to `sym`. The 
                                     associated data values of type `T` are default constructed.]]
    [[`sym.add(s1)(s2)...(sN)`]     [Add one or more symbols (`s1`...`sN`) to `sym`. The 
                                     associated data values of type `T` are default constructed.]]
    [[`sym.add(s1, d1)(s2, d2)...(sN, dN)`]
                                    [Add one or more symbols (`s1`...`sN`)
                                    with associated data (`d1`...`dN`) to `sym`.]]
    [[`sym -= s1, s2, ..., sN`]     [Remove one or more symbols (`s1`...`sN`) from `sym`.]]
    [[`sym.remove(s1)(s2)...(sN)`]  [Remove one or more symbols (`s1`...`sN`) from `sym`.]]
    [[`sym.clear()`]                [Erase all of the symbols in `sym`.]]
    [[`sym.at(s)`]                  [Return a reference to the object associated
                                    with symbol, `s`. If `sym` does not already
                                    contain such an object, `at` inserts the default
                                    object `T()`.]]
    [[`sym.find(s)`]                [Return a pointer to the object associated
                                    with symbol, `s`. If `sym` does not already
                                    contain such an object, `find` returns a null
                                    pointer.]]
    [[`sym.for_each(f)`]            [For each symbol in `sym` `s` invoke 
                                    `f(typename Lookup::value_type)`.]]
    [[`sym.name()`]                 [Retrieve the current name of the symbols object.]]
    [[`sym.name(name)`]             [Set the current name of the symbols object to be `name`.]]
]

The symbols generator uses the supplied attribute as the key to be looked up 
in the internal associative container. If the key exists the generator emits 
the associated value and succeeds (unless the underlying output stream reports 
an error). If the value type stored in the symbol generator is __unused_type__
it will emit the key instead. If the key does not exist the generator fails 
while not emitting anything. 

[heading Attributes]

The attribute of `symbol<Attrib, T>` is `Attrib`. 

If the supplied attribute is a __fusion__ sequence, then the symbol table 
generator will use the first element of that __fusion__ sequence as the key 
to be used for lookup. The type of that first element needs to be convertible 
to `Attrib`. In this case the second element of the __fusion__ sequence is used
as the attribute while calling a generator derived from the value stored in the 
symbol table for the found entry.

If the supplied attribute is a container type (__customize_is_container__ 
resolves to `mpl::true_`), then the symbol table generator will use the first 
element stored in that container as the key to be used for lookup. The 
`value_type` (returned by __customize_container_value__) has to be convertible 
to `Attrib`. In this case the second element stored in that container is used
as the attribute while calling a generator derived from the value stored in the 
symbol table for the found entry.

If the supplied attribute is not a __fusion__ sequence and not a container
type, the supplied attribute is directly used as the key for item lookup. The
attribute is used as the attribute while calling a generator derived from the 
value stored in the symbol table for the found entry.

In any case, because the supplied key (i.e. either the first element of the 
__fusion__ sequence, the first container element, or the attribute otherwise)
is passed as the attribute to a generator derived from the value
stored in the symbol table for the found entry, the symbol table may store 
generators, which will produce output based on that value. For instance:

    // The symbol table maps a single character key to a rule<>
    // The rule<> exposes an attribute of char as well
    rule<output_iterator_type, char()> r1 = char_;
        
    symbols<char, rule<output_iterator_type, char()> > sym;
    sym.add
        ('j', r1.alias())
        ('h', r1.alias())
        ('t', r1.alias())
        ('k', r1.alias())
    ;

    // Supplying a fusion vector as the attribute will use the first element
    // (the 'j') as the key to be looked up, while the second element (the 'J') 
    // is passed on as the attribute to the rule<> stored in the symbol table. 
    // Consequently, the example generates a single 'J'.
    BOOST_ASSERT(test("J", sym, make_vector('j', 'J')));

[heading Complexity]

The default implementation uses a `std::map<>` or a `std::set<>` with a 
complexity of:

[:O(log n)]

Where n is the number of stored symbols.

[heading Example]

[note The test harness for the example(s) below is presented in the
      __karma_basics_examples__ section.]

Some includes:

[reference_karma_includes]

Some using declarations:

[reference_karma_using_declarations_symbols]

Basic usage of `symbol` generators:

[reference_karma_symbols]

[endsect] [/ symbols]

[endsect]
