A list consisting of List1 followed by List2.
Appends lists List1 and List2 to form List3:
| ?- append([a,b], [a,d], X). X = [a,b,a,d] | ?- append([a], [a], [a]). no | ?- append(2, [a], X). no
Takes List3 apart:
| ?- append(X, [e], [b,e,e]). X = [b,e] | ?- append([b|X], [e,r], [b,o,r,e,r]). X = [o,r] | ?- append(X, Y, [h,i]). X = , Y = [h,i] ; X = [h], Y = [i] ; X = [h,i], Y =  ; no
Suppose L is bound to a proper list. That is, it has the form [T1,...,Tn] for some n. In that instance, the following things apply:
)has at most one solution, whatever X and Y are, and cannot backtrack at all.
)has at most n+1 solutions, whatever X and Y are, and though it can backtrack over these it cannot run away without finding a solution.
), however, can backtrack indefinitely if X and Y are variables.
The following examples are
perfectly ordinary uses of
To enumerate adjacent pairs of elements from a list:
next_to(X, Y, (*in*) List3) :- append(_, [X,Y|_], List3).
To check whether Word1 and Word2 are the same except for
a single transposition. (
library(lists) would be
better for this task.)
one_transposition(Word1, Word2) :- append(Prefix, [X,Y|Suffix], Word1), append(Prefix, [Y,X|Suffix], Word2). | ?- one_transposition("fred", X). X = "rfed" ; X = "ferd" ; X = "frde" ; no
Given a list of words and commas, to backtrack through the phrases delimited by commas:
comma_phrase(List3, Phrase) :- append(F, [','|Rest], List3), !, ( Phrase = F ; comma_phrase(Rest, Phrase) ). comma_phrase(List3, List3). | ?- comma_phrase([this,is,',',um,',',an, example], X). X = [this,is] ; X = [um] ; X = [an,example] ; no