copy_term/2
Module: builtins
copy_term/2 — make copy of a term
FORMS
copy_term(TermIn,TermOut)
DESCRIPTION
copy_term/2 will copy the term TermIn and unify this copy with TermOut. Unbound variables in TermIn and TermOut will not be shared between the two terms; i.e., uninstantiated variables occurring in TermIn will be replaced in TermOut by new uninstantiated variables not occurring in TermIn.
EXAMPLES
?- copy_term(f(X,g(Y,X)),Z).
X=X
Y=Y
Z=f(_A,g(_B,_A))
yes.
?- Y=f(9,rr), copy_term(Y, X), X==Y.
Y=f(9,rr)
X=f(9,rr)
yes.
?- Y=f(9,r, H), copy_term(Y, X), write(x=X),nl, X==Y.
x = f(9,r,_6203)
no.
NOTES
copy_term/2 is useful in situations involving destructive assignment. It is useful not only for the obvious situation of making a copy which is then destructively modified, but also for avoiding certain problems regarding structures becoming uninstantiated upon backtracking, as in findall, bagof, etc. It is also useful when using access predicates created with either make_gv/1 or make_hashtable/1. See make_gv/1 for further discussion.