retract ( head-def -- )

Vocabulary

logic

Inputs

head-def

a logic predicate

Outputs

None

Word description

Removes the first definition that matches the given head information.

Examples

USING: logic prettyprint ; IN: scratchpad LOGIC-PRED: mouseo SYMBOLS: Jerry Nibbles ; { mouseo Jerry } fact { mouseo Nibbles } fact { mouseo X } query . { mouseo Jerry } retract { mouseo X } query .
{ H{ { X Jerry } } H{ { X Nibbles } } } { H{ { X Nibbles } } }

See also

retract-all, clear-pred

Definition

USING: accessors kernel logic.private sequences ;

IN: logic

:: retract ( head-def -- )
    head-def replace-'__' def>goal :> head-goal head-goal pred>>
    defs>> :> defs defs
    [ first <env> head-goal <env> V{ } clone <env> (unify*) ]
    find
    [ head-goal pred>> [ remove-nth! ] change-defs drop ]
    [ drop ] if ;