When a call to a procedure in this prelude results in an error, the
called procedure signals the error in some particular way and also
sets a global errno to a code describing the error. For
example, trying to opening a file that doesn’t exist will result in
fopen returning -1, which signals an error. The caller can
then inspect the global errno to see what particular error
prevented the operation to be completed: in this case, errno
will contain the error code corresponding to “file doesn’t exist”.
= int ¶This procedure yields the current value of the global errno.
The yielded value reflects the error status of the last executed POSIX
prelude operation.
= (int ecode) string ¶This procedure gets an error code and yields a string containing an
explanatory short description of the error. It is typical to pass the
output of errno to this procedure.
= (string msg) void ¶This procedure prints the given string msg in the standard
error output, followed by a colon character, a space character and
finally the string error of the current value of errno.