Prolog - Input and output

• Prolog uses the write predicate to present output to the user.

• Prolog uses the read predicate to read Terms from standard input. Standard involve must be followed by a period.

• LPA Prolog has the ability to create and manipulate dialog boxes.

test :-

write('Enter an atom'),

nl,

read(Atom),

atom(Atom),

assertz(Atom),

call(Atom),

listing.

NOTE: Some new built in predicates are introduced here.

Listing the contents

• You can use the listing predicate to list all dynamic predicates loaded.

• Alternately you can use a combination of write and the fail predicate.

• See capitals.pl

capital_of(georgia,atlanta).

capital_of(california,sacramento).

capital_of(florida,tallahassee).

capital_of(maine,augusta).

print_capitals :-

capital_of(State,City),

write(City), write(‘ is the capital of),

write(State), nl,

fail.

Loading Prolog terms

• To load clauses from the listing file into the Prolog interpreter use consult or reconsult

• ensure_loaded can be used to automatically load files when a buffer is being consulted.

• You can use the compiler directive :- in front of any of these commands and they will be carried out as a buffer is being re-consulted.

File handling

• This see predicate is used to stream input from a file.

• After the see predicate all reads refer to the input stream from the file.

• seen is used to close input stream.

• That tell predicate is used to redirect output to a file.

• All subsequent write statements are redirected to the file named in tell predicate.

• told closes the output stream.

You can see these features in learner.pl used with kb.pl

A sample Expert system

• See car.pl• Basic Components

– Inference Engine (Prolog’s built in backward chaining).

– Knowledge base defect_may_be/1.

– Knowledge acquisition mechanism ask_questions/1.

– Recording what the user answers stored_answer/2.

– An explanation facility explain/1.