The facilities described in this section are exported by the (rnrs
io ports) module.
buffer-mode-symbol must be a symbol whose name is one of
none, line, and block. The result is the
corresponding symbol, and specifies the associated buffer mode.
See Buffering, for a discussion of these different buffer modes. To
control the amount of buffering, use setvbuf instead. Note that
only the name of buffer-mode-symbol is significant.
See Buffering, for a discussion of port buffering.
Returns #t if the argument is a valid buffer-mode symbol, and
returns #f otherwise.
When opening a file, the various procedures accept a file-options
object that encapsulates flags to specify how the file is to be
opened. A file-options object is an enum-set (see rnrs enums)
over the symbols constituting valid file options.
A file-options parameter name means that the corresponding argument must be a file-options object.
Each file-options-symbol must be a symbol.
The file-options syntax returns a file-options object that
encapsulates the specified options.
When supplied to an operation that opens a file for output, the
file-options object returned by (file-options) specifies that the
file is created if it does not exist and an exception with condition
type &i/o-file-already-exists is raised if it does exist. The
following standard options can be included to modify the default
behavior.
no-createIf the file does not already exist, it is not created;
instead, an exception with condition type &i/o-file-does-not-exist
is raised.
If the file already exists, the exception with condition type
&i/o-file-already-exists is not raised
and the file is truncated to zero length.
no-failIf the file already exists, the exception with condition type
&i/o-file-already-exists is not raised,
even if no-create is not included,
and the file is truncated to zero length.
no-truncateIf the file already exists and the exception with condition type
&i/o-file-already-exists has been inhibited by inclusion of
no-create or no-fail, the file is not truncated, but
the port’s current position is still set to the beginning of the
file.
These options have no effect when a file is opened only for input. Symbols other than those listed above may be used as file-options-symbols; they have implementation-specific meaning, if any.
Note: Only the name of file-options-symbol is significant.
maybe-transcoder must be either a transcoder or #f.
The open-file-input-port procedure returns an
input port for the named file. The file-options and
maybe-transcoder arguments are optional.
The file-options argument, which may determine various aspects of
the returned port, defaults to the value of (file-options).
The buffer-mode argument, if supplied,
must be one of the symbols that name a buffer mode.
The buffer-mode argument defaults to block.
If maybe-transcoder is a transcoder, it becomes the transcoder associated with the returned port.
If maybe-transcoder is #f or absent,
the port will be a binary port and will support the
port-position and set-port-position! operations.
Otherwise the port will be a textual port, and whether it supports
the port-position and set-port-position! operations
is implementation-dependent (and possibly transcoder-dependent).
maybe-transcoder must be either a transcoder or #f.
The open-file-output-port procedure returns an output port for the named file.
The file-options argument, which may determine various aspects of
the returned port, defaults to the value of (file-options).
The buffer-mode argument, if supplied,
must be one of the symbols that name a buffer mode.
The buffer-mode argument defaults to block.
If maybe-transcoder is a transcoder, it becomes the transcoder associated with the port.
If maybe-transcoder is #f or absent,
the port will be a binary port and will support the
port-position and set-port-position! operations.
Otherwise the port will be a textual port, and whether it supports
the port-position and set-port-position! operations
is implementation-dependent (and possibly transcoder-dependent).