Re: How to replace a term to the inside of an other term?

student wrote:

If you wish to restrict the replacement of occurrences a functor that
may occur with different arities in the same term to occurrences that
have some particular arity then you must specify which one it is.

And why stop here? You may want to replace certain patterns
by other patterns, e.g.

?- replace(3*3 + 4*4, X*X, twice(X), Out).
X = X
Out = twice(3) + twice(4)
Yes (0.00s cpu)

?- replace(foo(1,foo(2,3)), foo(X,Y), bar(Y,X), Out).
X = X
Y = Y
Out = bar(bar(3, 2), 1)
Yes (0.00s cpu)

?- replace(foo(bar(baz)), foo(bar(X)), foobar(X), Out).
X = X
Out = foobar(baz)
Yes (0.00s cpu)



replace(In, OldTmpl, NewTmpl, Out) :-
functor(In, F, N),
functor(In1, F, N),
replace_args(N, In, OldTmpl, NewTmpl, In1),
( copy_term(OldTmpl-NewTmpl, Old-New), In1 = Old ->
Out = New
;
Out = In1
).

replace_args(I, In, OldTmpl, NewTmpl, Out) :-
( I > 0 ->
arg(I, In, InArg),
arg(I, Out, OutArg),
replace(InArg, OldTmpl, NewTmpl, OutArg),
I1 is I-1,
replace_args(I1, In, OldTmpl, NewTmpl, Out)
;
true
).


-- Joachim
.

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