5.5.3 Relationships Between Words

As well as word frequencies, predictive mode dictionaries can store certain relationships between words, to make learning more effective. With each word in a dictionary, a list of other words can be associated. Predictive mode automatically ensures that the weights of the words in this list are always at least as large as that of the word they are associated with.

This is most useful when one word is a prefix for another. For example, you may want to ensure that, however frequently the word ‘learning’ is used, the weight of the word ‘learn’ is always kept at least as big, so that it always takes precedence when completing.

The following functions allow you to define and undefine such prefix relationships (note that despite the command names and descriptions, predictive-define-prefix and predictive-undefine-prefix can be used to define relationships between any two words, not just prefixes; however, predictive-define-all-prefixes and the predictive-auto-define-prefixes feature can only define actual prefix relationships):

predictive-define-prefix

Define one word to be a prefix of another. Predictive mode will ensure that the weight of the “prefix” word is always at least as large as that of the other. (Note that the word does not actually have to be a prefix of the other; this can be used to define a relationship between any two words, so that the weight of one is always larger than the other.)

predictive-undefine-prefix

Remove a “prefix” definition. (As for predictive-define-prefix, the word does not actually have to be a prefix of the other.)

predictive-define-all-prefixes

Add the given prefix to the prefix definitions of all words that for which it is a prefix, or define all possible prefix relationships in the dictionary if no explicit prefix is supplied. In the latter case, a numerical prefix argument sets a minimum word length for which to define a prefix relationship; relationships are only defined for words that are at least this long (the prefixes defined for those words can still be any length).

predictive-undefine-all-prefixes

The analogue of predictive-define-all-prefixes. Remove the given prefix from the prefix definitions of all words, or remove all prefix definitions in the dictionary if no explicit prefix is supplied. In the latter case, a numerical prefix argument sets a minimum word length for which to undefine prefix relationships (the length of the prefixes that are undefined is still not restricted in any way).

The following variable is used to help guess a likely prefix as a default for predictive-define-prefix and predictive-undefine-prefix. It's default value is only appropriate for English.

predictive-guess-prefix-suffixes

List of suffixes to use when guessing a likely prefix for a word. The suffixes a tried in the order they appear in the list, and the first one that matches the end of the word is used: the guessed prefix is the original word with the suffix removed.

Ensuring that prefixes take precedence when completing words is almost always a good idea. It makes predictive completion much more convenient (especially dynamic completion, see Dynamic Completion). Therefore, predictive mode includes a feature that, when enabled (the default), automatically defines all the prefix relationships whenever a word is added to a dictionary.

predictive-auto-define-prefixes

When non-nil, predictive mode will automatically update all prefix relationships for a word in a dictionary when the word is added. The new word will always take precedence over any word that is an extension of it, and in their turn any words that are prefixes of the new word will take precedence over it.