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When opening a file, the various procedures in this library 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 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) (without
arguments) 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.
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