Require Import elpi.elpi.

Elpi Db age.db lp:{{
  pred age o:string, o:int.
  :name "age.fail"
  age Name _ :- coq.error "I don't know who" Name "is!".
}}.

Elpi Command set_age.
Elpi Accumulate Db age.db.
Elpi Accumulate lp:{{
  main [str Name, int Age] :-
    coq.say "Pre" Name Age,
    Clause = (age Name Age),
    coq.elpi.accumulate _ "age.db" (clause _ (before "age.fail") Clause),
    Clause => (
      age Name AgeDb,
      coq.say "Post" Name AgeDb
   ).
}}.
Elpi Typecheck.

Elpi set_age "alice" 21.