Prolog IntList definition

Question

hill(+IntList) succeeds if IntList consists of monotonically increasing >integers followed by monotonically decreasing integers. For example, >[1,2,5,8,11,6,3,-1

Answer 1

Use clpfd!

:- use_module(library(clpfd)).

We don't need to worry about getting recursion right if we use append/3 and chain/2 like this:

hill(Zs) :-
   Ascending0 =   [_|_],
   Descending = [M,_|_],
   append(Ascending0,Descending,Zs),
   append(Ascending0,[M],Ascending),
   chain(Ascending ,#<),
   chain(Descending,#>).

Let's run the queries the OP gave!

?- hill([1,2,5,8,11,6,3,-1]).
  true                               % as expected
; false.

?- hill([1,2,5,8,11,6,9,3,-1]).
false.                               % as expected

?- hill([1,2,3,4,5,6]).
false.                               % as expected