dcg

I'm trying to modify a list by search and replace, was wondering how do I search through a list with the search term as a list as well? Lets say I have a list [1,2,3,4] I want to single out the 2 and 3 and replace it with 5,6 so ideally I could have a predicate: search_and_replace(Search_Term, Replace_Term, Target_List, Result_List). eg. search_and_replace([2,3], [5,6], [1,2,3,4], Result_List), write(Result_List). You can use append/2 as follows : replace(ToReplace, ToInsert, List, Result) :- once(append([Left, ToReplace, Right], List)), append([Left, ToInsert, Right], Result). With or without

This question starts from Mat's answer to Algorithm improvement for enumerating binary trees which has only one input value that determines the number of all nodes for the binary tree, and the need to be able to have two input values with one being the number of unary nodes and the other being the number of binary nodes. While I was able to derive a solution by using listing/1 and threading extra state variables: e(t, B, B, U, U). e(u(E), B0, B1, [_|U0], U1) :- e(E, B0, B1, U0, U1). e(b(E0, E1), [_|B0], B2, U0, U2) :- e(E0, B0, B1, U0, U1), e(E1, B1, B2, U1, U2). e(U,B,Es) :- length(Bs, B),

So i got this for powerset: powerset([], []). powerset([H|T], P) :- powerset(T,P). powerset([H|T], [H|P]) :- powerset(T,P). This generates all sets of a list. Is it possible to generate all sets in list order. Example: List = [a,b,c] I want to get [a],[a,b],[a,b,c],[b],[b,c],[c] Note there is no [a,c] in this list of subsets since these are subsets starting from the left and going to the right. I've tried using a combination of append and recursion, but that didn't work out as i wanted it to. Little stumped at this point. Thanks. How about powerset(L, [H|T]):- append([H|T], _, L). powerset([_

Can I get a recursive Prolog predicate having two arguments, called reverse, which returns the inverse of a list: Sample query and expected result: ?- reverse([a,b,c], L). L = [c,b,a]. A recursive Prolog predicate of two arguments called palindrome which returns true if the given list is palindrome. Sample query with expected result: ?- palindrome([a,b,c]). false. ?- palindrome([b,a,c,a,b]). true. Ad 1: It is impossible to define reverse/2 as a ( directly edit thx to @repeat: tail) recursive predicate - unless you permit an auxiliary predicate. Ad 2: palindrome(X) :- reverse(X,X). But the

is it possible to get all elements from list of lists in Prolog? Something like: We have getElements([[[a,b,[c]],d,e],f,g,[h,[i,j]]],S) and the result is: S = [a,b,c,d,e,f,g,h,i,j] ... Thanks for help. magus In SWI-Prolog (and maybe others), you can use flatten/2 : ?- flatten([[[a,b,[c]],d,e],f,g,[h,[i,j]]], S). S = [a, b, c, d, e, f, g, h, i|...]. Note that the SWI-Prolog manual page for flatten/2 includes the following statement: Ending up needing flatten/3 often indicates, like append/3 for appending two lists, a bad design. However, the page doesn't say whether there is another native

I'm looking for a way to build an Expression Tree in Prolog. I already did some experiments and came up with the following working code (that will only handle constants and the plus expression): const(_). plus(_, _). eval(const(R), R). eval(plus(A, B), R) :- number(A), number(B), R is A+B. eval(plus(A, B), R) :- number(A), eval(B, B_R), R is A+B_R. eval(plus(A, B), R) :- eval(A, A_R), number(B), R is A_R+B. eval(plus(A, B), R) :- eval(A, A_R), eval(B, B_R), R is A_R+B_R. Is there any simpler alternative to this approach? Will I have to define these 4 cases for each one of the operators I plan

I'd like to read a plain text file and apply a predicate to each line (the predicates contain write which does the output). How would I do that? In SWI-Prolog, the cleanest solution is to write a DCG that describes what a "line" is, then call a predicate for each line. Use library(pio) to apply the DCG to a file. EDIT : As requested, consider: :- use_module(library(pio)). lines([]) --> call(eos), !. lines([Line|Lines]) --> line(Line), lines(Lines). eos([], []). line([]) --> ( "\n" ; call(eos) ), !. line([L|Ls]) --> [L], line(Ls). Sample usage: ?- phrase_from_file(lines(Ls), 'your_file.txt').

I've only been working with Prolog for a couple days. I understand some things but this is really confusing me. I'm suppose to write a function that takes a list and flattens it. ?- flatten([a,[b,c],[[d],[],[e]]],Xs). Xs = [a,b,c,d,e]. % expected result The function takes out the inner structures of the list. This is what I have so far: flatten2([],[]). flatten2([Atom|ListTail],[Atom|RetList]) :- atom(Atom), flatten2(ListTail,RetList). flatten2([List|ListTail],RetList) :- flatten2(List,RetList). Now, this works when I call: ?- flatten2([a,[b,c],[[d],[],[e]]], R). R = [a,b,c,d,e]. % works as