stream-start-line-p

Arguments: stream

This is a predicate which returns t if stream is positioned at the beginning of a line, else returns nil. It is permissible to always return nil. This is used in the implementation of fresh-line. Note that while a value of 0 from stream-line-column also indicates the beginning of a line, there are cases where stream-start-line-p can be meaningfully implemented although stream-line-column can't be. For example, for a window using variable-width characters, the column number isn't very meaningful, but the beginning of the line does have a clear meaning. The default method for stream-start-line-p on class fundamental-character-output-stream uses stream-line-column, so if that is defined to return nil, then a method should be provided for either stream-start-line-p or stream-fresh-line.

See also streams.htm for general information on streams in Allegro CL.

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Created 2012.5.30.