About the Shen Prolog

[Antti Ylikoski]

One individual in this group said that his issue of The Book of Shen

has virtually nothing on Prolog.  I decided to write some demos for

the Shen Prolog to help such points.

It very soon turns out that one really does need the capability to

call Shen functions from inside the Shen Prolog.  The below attempt to

write the C. A. R. Hoare's Quicksort cannot be written without the

capability to call the Shen/Common LISP comparison predicates "<",

">", ">=" etc etc from inside the Shen Prolog.

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

\*

 *

 * Shen demo #n+1 by AJY 2015-05-25

 *

 * C A R Hoare's Quicksort with Shen

 *

 * Adapted from the author's files for Mats Carlsson's YAQ LISP based

 * Prolog, which has the functionality to call LISP from Prolog

 * predicates. 

 *\

\* First some necessary list op machinery:

 *\

(defprolog qappend

  [] X X <--;

  [X | Y] Z [X | U] <--

    (qappend Y Z U);)

\* H is the pivot element *\

(defprolog quisort-split

  H [A | X] [A | Y] Z <--

    (=< A H)

    (quisort-split H X Y Z);

  H [A | X] Y [A | Z] <--

    (> A H)

    (quisort-split H X Y Z);

  Ignore [] [] [] <-- ;)

(defprolog quisort

  [] [] <--;

  [H | T] S <--

    (quisort-split H T A B)

    (quisort A A1)

    (quisort B B1)

    (qappend A1 [H | B1] S);)

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

yours, AJY

[Mark Tarver]

This facility exists already.

Mark

[Mark Tarver]

see http://www.shenlanguage.org/learn-shen/shendoc.htm#Prolog

fwhen and when

mark

[Antti Ylikoski]

Thank you Mark, I was being pretty careless.

Following is a working Quicksort for those who feel they need some demos:

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

\*

 *

 * Shen demo #n+1 by AJY 2015-05-25

 *

 * C A R Hoare's Quicksort with Shen

 *

 * Adapted from the author's files for Mats Carlsson's YAQ LISP based

 * Prolog

 *\

\* First some necessary list op machinery:

 *\

(defprolog qappend

  [] X X <--;

  [X | Y] Z [X | U] <--

    (qappend Y Z U);)

\* H is the pivot element *\

(defprolog quisort-split

  H [A | X] [A | Y] Z <--

    (when (<= A H))

    (quisort-split H X Y Z);

  H [A | X] Y [A | Z] <--

    (when (> A H))

    (quisort-split H X Y Z);

  Ignore [] [] [] <-- ;)

\\ (prolog? (quisort [88 1 6 3 7 3 4 5 777 6 8 8 99] Sorted) (return Sorted))

(defprolog quisort

  [] [] <--;

  [H | T] S <--

    (quisort-split H T A B)

    (quisort A A1)

    (quisort B B1)

    (qappend A1 [H | B1] S);)

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

yours, A. J. Y.

[Mark Tarver]

It's ok - a lot of stuff to learn.

mark

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