110 lines
2.6 KiB
Text
110 lines
2.6 KiB
Text
# Working With The Dictionary
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The Dictionary is a linked list containing the dictionary
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headers.
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## Namespace
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Words operating on the dictionary are in the `d:` namespace.
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## Variables
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`Dictionary` is a variable holding a pointer to the most recent
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header.
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## Header Structure
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Each entry follows the following structure:
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Offset Contains
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------ ---------------------------
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0000 Link to Prior Header
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0001 Link to XT
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0002 Link to Class Handler
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0003 Source Identifier
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0004+ Word name (null terminated)
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RETRO provides words for accessing the fields in a portable
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manner. It's recommended to use these to allow for future
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revision of the header structure.
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## Accessing Fields
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Given a pointer to a header, you can use `d:xt`, `d:class`,
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and `d:name` to access the address of each specific field.
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There is no `d:link`, as the link will always be the first
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field.
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## Shortcuts For The Latest Header
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RETRO provides several words for operating on the most recent
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header.
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`d:last` returns a pointer to the latest header. `d:last.xt`
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will give the contents of the `d:xt` field for the latest
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header. There are also `d:last.class` and `d:last.name`.
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## Adding Headers
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Two words exist for making new headers. The easy one is
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`d:create`. This takes a string for the name and makes a
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new header with the class set to `class:data` and the XT
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field pointing to `here`.
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Example:
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```
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'Base d:create
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```
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The other is `d:add-header`. This takes a string, a pointer
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to the class handler, and a pointer for the XT field and
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builds a new header using these.
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Example:
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```
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'Base &class:data #10000 d:add-header
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```
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## Searching
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RETRO provides two words for searching the dictionary.
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`d:lookup` takes a string and tries to find it in the
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dictionary. It will return a pointer to the dictionary header
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or a value of zero if the word was not found.
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`d:lookup-xt` takes a pointer and will return the dictionary
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header that has this as the `d:xt` field, or zero if no match
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is found.
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## Iteration
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You can use the `d:for-each` combinator to iterate over all
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entries in the dictionary. For instance, to display the names
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of all words:
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```
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[ d:name s:put sp ] d:for-each
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```
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For each entry, this combinator will push a pointer to the
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entry to the stack and call the quotation.
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## Listing Words
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Most Forth systems provide WORDS for listing the names of all
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words in the dictionary. RETRO does as well, but this is named
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`d:words`.
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This isn't super useful as looking through several hundred
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names is annoying. RETRO also provides `d:words-with` to help
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in filtering the results.
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Example:
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```
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'class: d:words-with
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```
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