| CallbackResult-class {Aspell} | R Documentation |
These classes provide a way to provide structure
to the concept of a function that is used as
an asynchronous callback or handler.
The idea is that one associates a callback function
with something that generates events.
When an event occurs, the callback function is
invoked.
We use this in the Aspell package for checking the spelling
of words in a document. We pass the callback function
to spellDoc. It iterates over the content
of the document and when it encounters an mis-spelled word,
it invokes the callback function, providing it with
the mis-spelled word, its location, the entire text of the document
and the speller object responsible for performing the spell-checking.
The CallbackResult class is an extension of the basic notion
of a Callback function. This is used to provide a way to
retrieve the “answer” when the entire processing is done.
In this version, the CallbackResult provides information
about which variable in the environment of the callback
function contains the result. This allows the iterating function
to return the result at the end rather than requiring the caller
to access it separately.
We imagine that one would create derived/extended classes
from these that validate the formal arguments of the
specified function to match the event type.
Also, one might provide methods for getResult
to obtain the result from a Callback in different
ways than using a named variable. For instance, it
may involve dynamic computations.
Objects can be created by calls of the form new("CallbackResult", ...).
.Data:"function". This is the
callback function that is to be invoked when an event occurs.variable:"character". The name
of the variable within the
Class "Callback", directly.
Class "function", by class "Callback".
Class "OptionalFunction", by class "Callback".
Class "PossibleMethod", by class "Callback".
signature(doc = "ANY", wordHandler = "CallbackResult"):
check the spelling of the contents of a document and return the
results as gathered by the wordHandler object.
These classes are not specific to Aspell, but are here for the moment as there is no other good place to house them. The concept does arise in many places (e.g. GUIs, XML parsing) and we will want to move the code to a general package.
Duncan Temple Lang <duncan@wald.ucdavis.edu>