5.15.2 Why use word lists?
Here are some reasons why people use wordlists:
- To prevent a set of words from being used outside the context in which
they are valid. Two classic examples of this are an integrated editor
(all of the edit commands are defined in a separate word list; the
search order is set to the editor word list when the editor is invoked;
the old search order is restored when the editor is terminated) and an
integrated assembler (the op-codes for the machine are defined in a
separate word list which is used when a
CODE word is defined).
- To organize the words of an application or library into a user-visible
forth-wordlist or some other common wordlist) and a set
of helper words used just for the implementation (hidden in a separate
wordlist). This keeps
words' output smaller, separates
implementation and interface, and reduces the chance of name conflicts
within the common wordlist.
- To prevent a name-space clash between multiple definitions with the same
name. For example, when building a cross-compiler you might have a word
IF that generates conditional code for your target system. By
placing this definition in a different word list you can control whether
the host system's
IF or the target system's
IF get used in
any particular context by controlling the order of the word lists on the
search order stack.
The downsides of using wordlists are:
- Debugging becomes more cumbersome.
- Name conflicts worked around with wordlists are still there, and you
have to arrange the search order carefully to get the desired results;
if you forget to do that, you get hard-to-find errors (as in any case
where you read the code differently from the compiler;
help seeing which of several possible words the name resolves to in such
See displays just the name of the words, not what
wordlist they belong to, so it might be misleading. Using unique names
is a better approach to avoid name conflicts.
- You have to explicitly undo any changes to the search order. In many
cases it would be more convenient if this happened implicitly. Gforth
currently does not provide such a feature, but it may do so in the