package datalog

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package datalog
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Library
Module
Module type
Parameter
Class
Class type
module Const : CONST
type const = Const.t
val set_debug : bool -> unit

Terms

module T : sig ... end

Literals

module Lit : sig ... end

Clauses

module C : sig ... end

Substs

This module is used for variable bindings.

module Subst : sig ... end

Unification, matching...

type scope = Subst.scope
exception UnifFail

For unify and match_, the optional parameter oc is used to enable or disable occur-check. It is disabled by default.

val unify : ?oc:bool -> ?subst:Subst.t -> T.t -> scope -> T.t -> scope -> Subst.t

Unify the two terms.

val match_ : ?oc:bool -> ?subst:Subst.t -> T.t -> scope -> T.t -> scope -> Subst.t

match_ a sa b sb matches the pattern a in scope sa with term b in scope sb.

val alpha_equiv : ?subst:Subst.t -> T.t -> scope -> T.t -> scope -> Subst.t

Test for alpha equivalence.

val are_alpha_equiv : T.t -> T.t -> bool

Special version of alpha_equiv, using distinct scopes for the two terms to test, and discarding the result

val clause_are_alpha_equiv : C.t -> C.t -> bool

Alpha equivalence of clauses.

Special built-in functions

The built-in functions are symbols that have a special meaning. The meaning is given by a set of OCaml functions that can evaluate applications of the function symbol to arguments.

For instance, sum is a special built-in function that tries to add its arguments if those are constants.

Note that a constant will never be interpreted.

module BuiltinFun : sig ... end

The following hashtables use alpha-equivalence checking instead of regular, syntactic equality

module TVariantTbl : Hashtbl.S with type key = T.t
module CVariantTbl : Hashtbl.S with type key = C.t

Index

An index is a specialized data structured that is used to efficiently store and retrieve data by a key, where the key is a term. Retrieval involves finding all data associated with terms that match, or unify with, a given term.

module Index (Data : Hashtbl.HashedType) : sig ... end

Rewriting

Rewriting consists in having a set of rules, oriented from left to right, that we will write l -> r (say "l rewrites to r"). Any term t that l matches is rewritten into r by replacing it by sigma(r), where sigma(l) = t.

module Rewriting : sig ... end

DB

A DB stores facts and clauses, that constitute a logic program. Facts and clauses can only be added.

Non-stratified programs will be rejected with NonStratifiedProgram.

exception NonStratifiedProgram
module DB : sig ... end

Query

val ask : ?oc:bool -> ?with_rules:C.t list -> ?with_facts:T.t list -> DB.t -> T.t -> T.t list

Returns the answers to a query in a given DB. Additional facts and rules can be added in a local scope.

  • parameter oc

    enable occur-check in unification (default false)

val ask_lits : ?oc:bool -> ?with_rules:C.t list -> ?with_facts:T.t list -> DB.t -> T.t list -> Lit.t list -> T.t list

Extension of ask, where the query ranges over the list of variables (the term list), all of which must be bound in the list of literals that form a constraint.

ask_lits db vars lits queries over variables vars with the constraints given by lits.

Conceptually, the query adds a clause (v1, ..., vn) :- lits, which should respect the same safety constraint as other clauses.

  • returns

    a list of answers, each of which is a list of terms that map to the given list of variables.