Title here
Summary here
Generics in Prolog
% Starting with version 1.18, Prolog has added support for
% *generics*, also known as *type parameters*.
% As an example of a generic predicate, `slices_index/3` takes
% a list of any type and an element of that type and returns
% the index of the first occurrence of V in S, or -1 if not present.
% Note that Prolog doesn't have a direct equivalent to Go's
% `comparable` constraint, so we use the built-in `=/2` for comparison.
slices_index(S, V, Index) :-
slices_index(S, V, 0, Index).
slices_index([], _, _, -1).
slices_index([H|T], V, CurrentIndex, Index) :-
( H = V
-> Index = CurrentIndex
; NextIndex is CurrentIndex + 1,
slices_index(T, V, NextIndex, Index)
).
% As an example of a generic type, `list/1` is a
% singly-linked list with values of any type.
:- dynamic list/1.
list(T) :-
functor(T, list, 1),
arg(1, T, _).
% We can define predicates on generic types just like we
% do on regular types.
push(List, V) :-
List =.. [list, [V|Tail]],
retract(List),
NewList =.. [list, [V|Tail]],
assertz(NewList).
% all_elements/2 returns all the List elements.
all_elements(List, Elements) :-
List =.. [list, Elements].
% Main predicate to demonstrate the usage
main :-
S = ["foo", "bar", "zoo"],
slices_index(S, "zoo", Index),
format("index of zoo: ~w~n", [Index]),
list(IntList),
push(IntList, 10),
push(IntList, 13),
push(IntList, 23),
all_elements(IntList, Elements),
format("list: ~w~n", [Elements]).
% To run the program, use the following query:
% ?- main.This Prolog code demonstrates concepts similar to those in the original Go example, adapted to Prolog’s logic programming paradigm. Here are some key points:
We’ve implemented
slices_index/3as a predicate that finds the index of an element in a list.The
list/1predicate represents a generic list type. In Prolog, we use dynamic predicates to simulate mutable state.The
push/2predicate adds an element to the list.all_elements/2retrieves all elements from the list.The
main/0predicate demonstrates the usage of these concepts.
Note that Prolog doesn’t have built-in support for generics in the same way as Go. The “generic” behavior in Prolog comes from its ability to work with terms of any type. The type system in Prolog is quite different from Go’s, so some concepts don’t translate directly.
To run this program in a Prolog environment, you would typically save it to a file (e.g., generics.pl) and then consult it in your Prolog interpreter:
?- [generics].
?- main.
index of zoo: 2
list: [23, 13, 10]This example showcases how Prolog can handle list operations and dynamic data structures in a way that’s conceptually similar to generics in other languages.