- In each of the following functions,
the value of
EXPR
must be a string that
is a file name consistent with the operating system's naming conventions.
The value of the function has ISETL type file
and may be in
read
...
from
... and
print
...
to
...
statements to refer to that file.
openr(EXPR)
. If the file named by the value of
EXPR
exists,
then it is opened for reading, and the value of the function
is of type file.
If the file named by the value of
EXPR
does not exist,
then the value of the function is
OM
.
openw(EXPR)
. If the file named by the value of
EXPR
does not exist,
then it is created by the operating system externally to ISETL.
This file is opened for writing from the beginning,
so that anything previously in the file is destroyed.
The value of the function is of type file.
opena(EXPR)
. The same as
openw(EXPR)
except that if the file exists
its contents are not destroyed.
Anything that is written is appended to the file.
- In the following function, the value of
EXPR
must be of type file. The
file specified by this value is closed. Output files must be closed to
guarantee that all output has been stored by the operating system. All
files are closed automatically when ISETL is exited.
There is usually a system-imposed limit on the number of files
that may be open at one time, however, so it is a good idea to close files
when finished using them.
close(EXPR)
. The value of the function is
OM
.
- In the following function the value of
EXPR
must be of type file.
eof (EXPR)
. Test for having read past the end of an external file.