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Prompting functions are implemented as a recursive edit in the Echo Area buffer. Completion, help, and other parsing features are implemented by commands which are bound in Echo Area Mode.
A prompting function passes information down into the recursive edit by binding a collection of special variables.
The system binds this to a function that Confirm Parse calls. It does most of the work when parsing prompted input. Confirm Parse passes one argument, which is the string that was in parse-input-region when the user invokes the command. The function should return a list of values which are to be the result of the recursive edit, or nil indicating that the parse failed. In order to return zero values, a non-nil second value may be returned along with a nil first value.
This is the list of string-tables, if any, that pertain to this parse.
This is bound to the value of the :must-exist argument, and is referred to by the verification function, and possibly some of the commands.
When prompting the user, this is bound to a string representing the default object, the value supplied as the :default argument. Confirm Parse supplies this to the parse verification function when the parse-input-region is empty.
When prompting the user, if parse-default is nil, Hemlock displays this string as a representation of the default object; for example, when prompting for a buffer, this variable would be bound to the buffer name.
The kind of parse in progress, one of :file, :keyword or :string. This tells the completion commands how to do completion, with :string disabling completion.
The prompt being used for the current parse.
The help string or function being used for the current parse.
This variable holds a mark in the echo-area-buffer which is the position at which the parse began.
This variable holds a region with parse-starting-mark as its start and the end of the echo-area buffer as its end. When Confirm Parse is called, the text in this region is the text that will be parsed.
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