6. Writing programs to use Aspell

There are two main ways to use aspell from within your application. Through the external C API or through a pipe. The internal Aspell API can be used directly but that is not recommended as the actual Aspell API is constantly changing.

6.1 Through the C API

The Aspell library contains two main classes and several helper classes. The two main classes are AspellConfig and AspellSpeller The AspellConfig class is used to set initial defaults and to change spell checker specific options. The AspellSpeller class does most of the real work. It is responsible for managing the dictionaries, checking if a word is in the dictionary, and coming up with suggestions among other things. There are many helper classes the important ones are AspellWordList, AspellMutableWordList, Aspell*Enumeration. The AspellWordList classes is used for accessing the suggestion list, as well as the personal and suggestion word list currently in use. The AspellMutableWordList is used to manage the personal, and perhaps other, word lists. The Aspell*Enumeration classes are used for iterating through a list.

6.1.1 Usage

To use Aspell your application should include ``aspell.h''. In order to insure that all the necessary libraries are linked in libtool should be used to perform the linking. When using libtool simply linking with ``-laspell'' should be all that is necessary. When using shared libraries you might be able to simply link ``-laspell'', but this is not recommended.

When your application first starts you should get a new configuration class with the command:

AspellConfig * spell_config = new_aspell_config();

which will create a new AspellConfig class. It is allocated with new and it is your responsibility to delete it with delete_aspell_config. Once you have the config class you should set some variables. The most important one is the language variable. To do so use the command:

aspell_config_replace(spell_config, "lang", "en_US");

which will set the default language to use to American English. The language is expected to be the standard two letter ISO 639 language code, with an optional two letter ISO 3166 country code after an underscore. You can set the preferred size via the size option, any extra info via the jargon option, and the encoding via the encoding option. Other things you might want to set is the preferred spell checker to use, the search path for dictionary's, and the like see section 4.2 for a list of all available options.

When ever a new document is created a new AspellSpeller class should also be created. There should be one speller class per document. To create a new speller class use the new_aspell_speller and then cast it up using to_aspell_speller like so.

AspellCanHaveError * possible_err = new_aspell_speller(spell_config);

AspellSpeller * spell_checker = 0;

if (aspell_error_number(possible_err) != 0)

  puts(aspell_error_message(possible_err));

else

  spell_checker = to_aspell_speller(possible_err);

which will create a new AspellSpeller class using the defaults found in spell_config. To find out which dictionary is selected the lang, size, and jargon options may be examinded. To find out the exact name of the dictionary the master option way be examned as well as the master-flags opntions to see if any special flags that were passed on to the module. The module option way also be examed to figure out which speller module was selected, but since there is only one this option will always be the same.

If for some reason you want to use different defaults simply clone spell_config and change the setting like so:

AspellConfig * spell_config2 = aspell_config_clone(spell_config);

aspell_config_replace(spell_config2, "lang","nl");

possible_err = new_aspell_speller(spell_config2);

delete_aspell_config(spell_config2);

Once the speller class is created you can use the check method to see if a word in the document is correct like so:

int correct = aspell_speller_check(spell_checker, <word>, <size>);

<word> can is expected to a const char * character string. If the encoding is set to be ``machine unsigned 16'' or ``machine unsigned 32''. <word> is expected to be a cast from either const uint16_t * or const uint32_t* respectfully. uint16_t and uint32_t are generally unsigned short and unsigned int respectfully. <size> is the length of the string or -1 if the sting is null terminated. If the string is a cast from const uint16_t * or const uint32_t * then size is the amount of space in bytes the string takes up after being casted to const char * and not the true size of the string. Aspell_speller_check will return 0 is it is not found and non-zero otherwise.

If the word is not correct than the suggest method can be used to come up with likely replacements.

AspellWordList * suggestions = aspell_speller_suggest(spell_checker, <word>, <size>);

AspellStringEnumeration * elements = aspell_word_list_elements(suggestions);

const char * word;

while ( (word = aspell_string_enumeration_next(aspell_elements) != NULL ) {

  // add to suggestion list

}

delete_aspell_string_manag(elements);

Notice how elements is deleted but suggestions is not. The value returned by suggestions is only valid to the next call to suggest. Once a replacement is made the store_repl method should be used to communicate the replacement pair back to the spell checker (see section 6.3 for why). It usage is as follows:

aspell_speller_store_repl(spell_checker, 

                          <misspelled word>, <size>,

                          <correctly spelled word>, <size>);

If the user decided to add the word to the session or personal dictionary the the word can be be added using the add_to_session or add_to_personal methods respectfully like so:

aspell_speller_add_to_session|personal(spell_checker, <word>, <size>);

It is better to let the spell checker manage these words rather than doing it your self so that the words have a change of appearing in the suggestion list.

Finally, when the document is closed the AspellSpeller class should be deleted like so.

delete_aspell_speller(spell_checker);

6.1.2 API Reference

Methods that return a boolean result generally return false on error and true other wise. To find out what went wrong use the error_number and error_message methods. Unless otherwise stated methods that return a ``const char *'' will return null on error. In general, the charter string returned is only valid until the next method which returns a ``const char *'' is called.

For the details of the various classes please see the header files. In the future I will generate class references using some automated tool.

6.1.3 Examples

Two simple examples are included in the examples directory. The ``example-c'' program demenstracts most of the Aspell library functionary and the ``list-dicts'' lists the available dictionaries.

6.1.4 Notes About Thread Safety

Read-only Aspell methods and functions should be thread safe as long as exceptions, new, delete, delete[], and STL allocators are thread safe. To the best of my knowledge gcc and egcs meet these requirements. It is up to the programmer to make sure multiple threads do not do thing such as change the dictionaries and add or delete items from the personal or session dictionaries.

6.2 Through A Pipe

When given the pipe or -a command aspell goes into a pipe mode that is compatible with ``ispell -a''. Aspell also defines its own set of extensions to ispell pipe mode.

6.2.1 Format of the Data Stream

In this mode, Aspell prints a one-line version identification message, and then begins reading lines of input. For each input line, a single line is written to the standard output for each word checked for spelling on the line. If the word was found in the main dictionary, or your personal dictionary, then the line contains only a '*'.

If the word is not in the dictionary, but there are suggestions, then the line contains an '&', a space, the misspelled word, a space, the number of near misses, the number of characters between the beginning of the line and the beginning of the misspelled word, a colon, another space, and a list of the suggestions separated by commas and spaces.

Finally, if the word does not appear in the dictionary, and there are no suggestions, then the line contains a '#', a space, the misspelled word, a space, and the character offset from the beginning of the line. Each sentence of text input is terminated with an additional blank line, indicating that ispell has completed processing the input line.

These output lines can be summarized as follows:

OK:

*

Suggestions:

& «original» «count» «offset»: «miss», «miss», ...

None:

# «original» «offset»

When in the -a mode, Aspell will also accept lines of single words prefixed with any of '*', '&', '@', '+', '-', '~', '#', '!', '%', or '^'. A line starting with '*' tells ispell to insert the word into the user's dictionary. A line starting with '&' tells ispell to insert an all-lowercase version of the word into the user's dictionary. A line starting with '@' causes ispell to accept this word in the future. A line starting with '+', followed immediately by a valid mode will cause aspell to parse future input according the syntax of that formatter. A line consisting solely of a '+' will place ispell in TEX/L^ATEX mode (similar to the -t option) and '-' returns aspell to its default mode (but these commands are obsolete). A line '~', is ignored for ispell compatibility. A line prefixed with '#' will cause the personal dictionaries to be saved. A line prefixed with '!' will turn on terse mode (see below), and a line prefixed with '%' will return ispell to normal (non-terse) mode. Any input following the prefix characters '+', '-', '#', '!', '~', or '%' is ignored, as is any input following. To allow spell-checking of lines beginning with these characters, a line starting with '^' has that character removed before it is passed to the spell-checking code. It is recommended that programmatic interfaces prefix every data line with an uparrow to protect themselves against future changes in Aspell.

To summarize these:

*«word»

Add a word to the personal dictionary

&«word»

Insert the all-lowercase version of the word in the personal dictionary

@«word»

Accept the word, but leave it out of the dictionary

#

Save the current personal dictionary

~

Ignored for ispell compatibility.

+

Enter TEX mode.

+«mode»

Enter the mode specified by «mode».

-

Enter the default mode.

!

Enter terse mode

%

Exit terse mode

^

Spell-check the rest of the line

In terse mode, Aspell will not print lines beginning with '*', which indicate correct words. This significantly improves running speed when the driving program is going to ignore correct words anyway.

In addition to the above commands which are designed for Ispell compatibility Aspell also supports its own extension. All Aspell extensions follow the following format.

$$«command» [data]

Where data may or may not be required depending on the particular command. Aspell currently supports the following command.

cs «option»,«value»

Change a configuration option.

cr «option»

Prints the value of a configuration option.

pp

Returns a list of all words in the current personal wordlist.

ps

Returns a list of all words in the current session dictionary.

l

Returns the current language name.

ra «mis»,«cor»

Add the word pair to the replacement dictionary for latter use. Returns nothing.

Anything returned is returned on its own line line. All lists returned have the following format

«num of items»: «item1», «item2», «etc»

(Part of the preceding section was directly copied out of the Ispell manual)

6.3 Notes of Storing Replacement Pairs

The store_repl method and the $$ra should be used because Aspell is able to learn from users misspellings. For example on the first pass a user misspells beginning as beging so aspell suggests:

begging, begin, being, Beijing, bagging, ....

However the user then tries "begning" and aspell suggests

beginning, beaning, begging, ...

so the user selects beginning. However than, latter on in the document the user misspelles it as begng (NOT beging). Normally aspell will suggest.

began, begging, begin, begun, ....

However becuase it knows the user mispelled beginning as beging it will instead suggest:

beginning, began, begging, begin, begun ...

I myself often misspelled beginning (and still do) as something close to begging and two many times wind up writing sentences such as "begging with ....".

Please also note that replacements commands has a memory. Which means if you first store the replacement pair:

sicolagest -> psycolagest

then store the replacement pair

psycolagest -> psychologist

The replacement pair

sicolagest -> psychologist

will also get stored so that you don't have to worry about it.