Page 217 - DCAP506_ARTIFICIAL_INTELLIGENCE

Unit 14: Prolog

In Prolog, streams for input and output are pointed to by alias names or via a system-defined Notes
terms which the Prolog system supplies with the predicateopen/3/4. The alias names are atoms.
The following table offers an outline of the streams which can be addressed. For addressing,
either the device name or the alias name can be used. The device name, or driver name, is used
only on opening a stream. The alias name displays a logical reference to a stream and discovers
a link among a stream and a name. The name is liberally selectable.
Stream Alias name

Standard input user_input
Standard output user_output
Standard error output user_error
Keyboard keyboard

Screen screen
The following defaults are fixed for the three standard streams:
Stream Default
Standard input Keyboard

Standard output Screen or window in which Prolog was started
Standard error output Screen or window in which Prolog was started and error message
window

You can also redefine the typical streams when calling Prolog.

Example: The file goals.pro is presumed to enclose the following goals:
Y is 3 + 4.
append(A, B, [a,b,c,d]).
atom(A).
If you then call Prolog and state the file as the input stream, these goals are developed
sequentially. The following output occurs on the screen:
$ prolog < goals.pro
Y = 7

yes

A = []
B = [a,b,c,d]
yes

no
$

When the end of the file is reached, Prolog is finished.
You can utilize the predicate stream_copy/2 to modify the standard stream assignments
throughout a Prolog session.

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