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6.18.5 Procedural ports

The underlying mechanism of procedural ports is very flexible, but I don't have Scheme interface yet, except the following ones:

Function: open-input-buffered-port filler buffer-size
Function: open-output-buffered-port flusher buffer-size
These procedures are deprecated and will be replaced by more general procedural APIs.

These are the Scheme interface to the "buffered port".

open-input-buffered-port creates and returns an input port, with associated buffer of size buffer-size. The data is read from the buffer. When the port is read and the buffer is empty, a procedure filler is called with one argument, the size of required data. filler must return a string (either complete or incomplete) of the specified size. It is permitted for filler to return a string shorter than the size, if not enough data is available. The behavior is undefined if filler returns larger string than specified. Note that the size of string matters, not the length of string. If filler finds that it reached EOF of its data source, it can return EOF. Retuning zero size string has the same effect as EOF. Initially, the buffer is empty, so filler is always called at the first attempt of reading from the port.

open-output-buffered-port creates and returns an output port, with associated buffer of size buffer-size. The data output to the port is accumulated in the buffer. When the buffer gets full, or flush is called on the port, a procedure flusher is called with an incomplete string to be flushed. flusher must return a number of bytes flushed, which must be the same as the size of the passed string. The string may shorter than buffer-size. When the port is closed, flusher is called with any data remaining in the buffer, then it is called again with #f to indicate the port is closed.

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This document was generated by Ken Dickey on November, 28 2002 using texi2html