Binary­Ports­Cowan

Introduction

This is my proposal for binary ports in small R7RS. It assumes, but partly overrides, PortsCowan. In particular, the version of the buffering key described there is replaced by the buffer key here.

Under this proposal, it is no longer true that all binary ports are also character ports. The user may create a file port that is either a character port, a binary port, or both. String ports are character ports; blob ports are binary ports.

Opening file ports

To open a binary file port, use any of the file-opening operations, passing the binary key with a true value. To open a character file port, use any of the file-opening operations, passing the character key with a true value. If either the character key or the binary key is not present, it is assumed to be false. However, if the whole file spec takes the form of a string rather than a list, the character key is assumed to be true.

If the buffer key is false, the port must not be buffered by the implementation. If the key is true or is not present, the port may be buffered. Buffered character ports that are not binary ports may have both a character buffer and a binary buffer, but buffered character ports that are binary ports must not have a character buffer. This permits safe interleaving of character and binary operations.

Here are the above rules in tabular form:

character	binary	buffer	returns:
false	false	false	undefined, no buffering
false	false	true	undefined
false	true	false	binary port, no buffer
false	true	true	binary port, may have buffer
true	false	false	character port, no buffer
true	false	true	character port, may have binary buffer and/or character buffer
true	true	false	character and binary port, no buffering
true	true	true	character and binary port, may have binary port, must not have character buffer

Operations on character and binary ports

• Character ports allow the read-char, peek-char, char-ready, and the layered read, write, and display operations; they answer #t to character-port?.

• Binary ports allow the read-u8, peek-u8, and u8-ready operations; they answer #t to binary-port?.

• Both kinds of ports can be handed to port?, input-port?, output-port?, character-port, binary-port, port-open?, close-input-port, and close-output-port.