Prolog substitution

Question

How can I replace a list with another list that contain the variable to be replaced. for example

rep([x, d, e, z, x, z, p], [x=z, z=x, d=c], R).
R = [z, c, e, x,         


        

Answer 1

Here's how you could proceed using if_/3 and (=)/3.

First, we try to find a single Key in a list of pairs K-V. An extra argument reifies search success.

pairs_key_firstvalue_t([]       ,_  ,_    ,false).
pairs_key_firstvalue_t([K-V|KVs],Key,Value,Truth) :-
   if_(K=Key,
       (V=Value, Truth=true),
       pairs_key_firstvalue_t(KVs,Key,Value,Truth)).

Next, we need to handle "not found" cases:

assoc_key_mapped(Assoc,Key,Value) :-
   if_(pairs_key_firstvalue_t(Assoc,Key,Value),
       true,
       Key=Value).

Last, we put it all together using the meta-predicate maplist/3:

?- maplist(assoc_key_mapped([x-z,z-x,d-c]), [x,d,e,z,a,z,p], Rs).
Rs = [z,c,e,x,a,x,p].                       % OK, succeeds deterministically