Note about the Shen Prolog

[Antti Ylikoski]

There is something which is there in typical LISP based Prolog

implementations, and which I would hope to have available in the Shen

Prolog.  It is the capability to call a Shen function from inside a

Shen Prolog predicate.

This capability is not there in the ISO Prolog.  I think there may be

there a FFI (Foreign Function Interface), but I cannot recall the ISO

standard as well as that.

The below attempt to write the Towers of Hanoi cannot be accomplished,

because there is no way to call the Shen function (output ...) from a

Shen Prolog predicate.

Or, the below program could be done, if there were the Prolog

predicates (write ...) and (writeln ...) in the Shen Prolog.

------------------------------------------------------------

\*

 * The Towers of Hanoi with the Shen Prolog.

 *

 * AJY 2015-05-24

 *

 *\

(defprolog hanoi

  N <-- (hanoi-move N left centre right);)

(defprolog hanoi-move

  0 Ignore1 Ignore2 Ignore3 <--;

  N A B C <--

    (is M (- N 1))

    (hanoi-move M A C B)

    (inform A B)

    (hanoi-move M C B A);)

(defprolog inform

  X Y <--

    (output "~%Move a disc from the ~A pole to the ~A pole.~%"

       X

   Y);)

------------------------------------------------------------

Yours, AJY

Helsinki, Finland