| retracts from the database the clauses which are unifiable with the argument.
retract(+Clause)
retract/1 retracts the first clause from the database which is unifiable with Clause .
If Clause is an atom or compound term whose principal functor is
different from ':-'/2 then Clause is the head and 'true' is the body
of the clause.
If Clause is a compound term whose principal functor is
':-'/2 then the left side (1st argument) of ':-' is the head
and the right side (2nd argument) the body
of the clause.
By backtracking it's possible to remove all clauses from the database,
which are unifiable with Clause.
Arguments
Clause atom or compound term
Examples
Assume that the database contains the clauses:
colour(blue).
colour(yellow).
colour(blue,yellow,green).
add(X,Y,Z) :- Z is X+Y.
f(a).
f(a) :- b.
| retract(f(a)).
| Succeeds. The database contains now the clauses:
colour(blue).
colour(yellow) :- true.
colour(blue,yellow) :- green.
add(X,Y,Z) :- Z is X+Y.
f(a) :- b.
|
Standard
This predicate is part of the ISO-Prolog Standard.
See also
asserta/1,
assertz/1,
abolish/1,
collect/3,
load/1,
unload/1,
load/1/2,
retractall/1.
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