Why 4Spell

Spell-checkers are nowadays widely used by word processors such as MS-Word and WordPerfect. They are extremely useful in correcting spelling errors, especially when writing in a non-native language.

TeX users often claim that TeX is better than those word processors, one wonders why there are so few good spell-checkers for TeX documents.

The main reason for this is that TeX documents not only contain "normal" words, but also complex TeX commands. And TeX commands may or may not take parameters, and parameters can be delimited in any imaginable way.

Within certain TeX environments you want the words to be checked (e.g. in tables) and in others you want them to be ignored (e.g. mathematics). All in all a complex situation if you realize that TeX commands, mathematics, and normal words needn't be separated by spaces and line feeds. Any good spell-checker for TeX documents requires a TeX parser that reads the text and decides whether or not a word or a part of the word should be spell-checked. Is writing a parser difficult? The answer probably would be "yes", since there aren't many spell-checkers around. 4Spell proofs that writing such a spell-checker can be done and that it's not that hard to write a spell-checker that can even do more than just TeX.

4Spell features

When we started to write 4TeX for Windows we still needed the "old" MS-Dos based AmSpell as a spell-checker. AmSpell has some serious problems/bugs when it checks your documents. We will not give you a list of those problems, but after AmSpell has checked your document you still can find spell-checking errors. This is because Amspell skips parts of your document and doesn't tell you it did.

In September 1998 we had the discussion if we needed to write a spell-checker for 4TeX and concluded that it should be too time consuming to write a good program, since TeX documents are too complex. As often, complex material tends to become much simpler when you have a closer look and spend more time thinking about the structures (TeX is a structured language isn't it). When starting to write 4Spell we started not on the spell-checking routines but on describing how a TeX document should be parsed through the spell-checker. This parsing is the engine of a good spell-checker (and here AmSpell makes it's mistakes). The spell-checking routines were supplied by Aleksander Simonic. Alex is the author of WinEdt, probably the best TeX-aware shareware editor there is for OS/2 and Windows. Cooperation with Alex means that we can all benefit from the same dictionaries, which makes maintenance a lot easier.

In the next section we will describe the parsing of a document, but now we will summarize some of 4Spell's features:

• Color highlighting, i.e. actions of the spell-checker are translated into coloring of words. This makes it easy to see how your document was interpreted and (possibly) changed. Not useful you would say!? But we discovered it is extremely powerful. For instance suppose you want mathematics to be skipped by the spell-checker and you have written in your document

   This example $x+y will trigger probblems
  

  Can you predict what will happen if you check your document: it will skip the whole document after the $x+y since the mathematics isn't ended properly. With AmSpell (or any other spell-checker) you couldn't see this. Now you can see and solve the problem just by looking at the colored document (i.e. everything after the mathematics statement $x+y is colored as mathematics)!
• Support of many languages: English (American and British), German, Dutch, French, Italian, Swedish, Danish, Russian, Polish, Spanish and South-African. Since all dictionaries are plain ASCII it is simple to add your own language or to update one of the dictionaries.
• Language switching within a document allows you to write multilingual documents and spell-check all parts according to the language in which they were written.
• Generation of a word list. All the different words that are used within your document can be listed. This can be useful in deciding which words should be considered for indexing.
• Generation of a logfile, showing all actions and changes that were performed.
• Basic statistics of the document and the spell-checking run are recorded.
• Many options that can be switched on/off to increase speed and/or performance.
• You can select fonts, font sizes and character sets. This makes it possible to spell-check non-western documents (Polish, Russian, etc).
• All colors used can be changed according to your personal preferences.
• 4Spell is format dependent. It maintains specific lists for each format that you use. Lists are defined for: accents, mathematical environments, commands, environments and verbatim commands. Also mathematics (between $...$ or $$...$$) can be ignored. Note that 4Spell supports (by default) the following formats:
  • TeX, LaTeX, and ConTeXt documents
  • Rich Text Format (RTF) documents
  • plain ASCII documents
  • HTML documents
  • BibTeX documents
  Indeed, not only TeX documents can be checked and hence makes 4Spell useful not only for TeX users. It is easy to add a format (e.g. ConTeXt) and make the changes to one of the format dependent lists and properties.
• 4Spell is language dependent. It maintains specific lists for each language that you use. Lists are defined for: automatic correction of typing mistakes, user specific words, and similar characters (used to specify which letters/characters are associated when looking for alternatives of an incorrect word).
• 4Spell can change its user-interface language on the fly (as 4TeX and 4Project).
• All settings for words, subwords, punctuation marks, etc., are format specific (see also the next section). This makes it easy to spell-check not only documents written in TeX, but also Plain ASCII, HTML, or RTF files. And of course you can define you own formats.
• You can check wether a word is used twice. For instance have a look at the word "one" in the next example:

  When you write very long lines and you end one
  one with a small word you tend to write certain words twice.
  

  4Spell will ask you if you want to delete the seconf "one" entry.
• 4Spell is lower and uppercase sensitive. For instance words as "This", "tHis" and "THis" can be changed automatically in "This". When checked by 4Spell it will give the suggestion "This" for the words used in this example.