A Datalog atom: a relation reference with a list of terms.
Atoms appear in rule heads and rule bodies. A head atom names the relation being derived. Body atoms name the relations being queried or matched.
An atom does not carry polarity (positive or negative). Polarity
is expressed at the rule body level via {:positive, atom} and
{:negative, atom} literals in ExDatalog.Rule.
Examples
iex> ExDatalog.Atom.new("parent", [{:var, "X"}, {:var, "Y"}])
%ExDatalog.Atom{relation: "parent", terms: [{:var, "X"}, {:var, "Y"}]}
iex> ExDatalog.Atom.new("person", [{:const, :alice}])
%ExDatalog.Atom{relation: "person", terms: [{:const, :alice}]}Summary
Functions
Returns the arity (number of terms) of the atom.
Constructs an atom from a shorthand tuple of the form {relation, terms}.
Constructs a new atom for the given relation and terms.
Returns true if the atom is structurally valid.
Returns all variable names in the atom's terms.
Types
@type t() :: %ExDatalog.Atom{relation: String.t(), terms: [ExDatalog.Term.t()]}
Functions
@spec arity(t()) :: non_neg_integer()
Returns the arity (number of terms) of the atom.
Examples
iex> ExDatalog.Atom.arity(ExDatalog.Atom.new("parent", [{:var, "X"}, {:var, "Y"}]))
2
iex> ExDatalog.Atom.arity(ExDatalog.Atom.new("node", [{:const, :a}]))
1@spec from_tuple({String.t(), [ExDatalog.Term.shorthand()]} | t()) :: t()
Constructs an atom from a shorthand tuple of the form {relation, terms}.
Each term in the list is converted using Term.from/1, which follows the
Prolog convention: uppercase atoms become variables, lowercase atoms and
other values become constants, and :_ becomes a wildcard.
Accepts either a {relation, terms} tuple or an existing %Atom{} struct
(passed through unchanged).
Examples
iex> ExDatalog.Atom.from_tuple({"parent", [:X, :Y]})
%ExDatalog.Atom{relation: "parent", terms: [{:var, "X"}, {:var, "Y"}]}
iex> ExDatalog.Atom.from_tuple({"role", [:User, :_ ]})
%ExDatalog.Atom{relation: "role", terms: [{:var, "User"}, :wildcard]}
iex> ExDatalog.Atom.from_tuple({"value", [:X, 42]})
%ExDatalog.Atom{relation: "value", terms: [{:var, "X"}, {:const, 42}]}@spec new(String.t(), [ExDatalog.Term.t()]) :: t()
Constructs a new atom for the given relation and terms.
Examples
iex> ExDatalog.Atom.new("edge", [{:var, "X"}, {:var, "Y"}])
%ExDatalog.Atom{relation: "edge", terms: [{:var, "X"}, {:var, "Y"}]}
iex> ExDatalog.Atom.new("fact", [{:const, 42}, :wildcard])
%ExDatalog.Atom{relation: "fact", terms: [{:const, 42}, :wildcard]}Returns true if the atom is structurally valid.
Valid means: non-empty relation name, all terms are valid ExDatalog.Term.t().
Examples
iex> ExDatalog.Atom.valid?(ExDatalog.Atom.new("parent", [{:var, "X"}, {:var, "Y"}]))
true
iex> ExDatalog.Atom.valid?(%ExDatalog.Atom{relation: "", terms: [{:var, "X"}]})
false
iex> ExDatalog.Atom.valid?(%ExDatalog.Atom{relation: "parent", terms: [:bad]})
false@spec variables(t()) :: [ExDatalog.Term.var_name()]
Returns all variable names in the atom's terms.
Examples
iex> ExDatalog.Atom.variables(ExDatalog.Atom.new("parent", [{:var, "X"}, {:const, :alice}, {:var, "Y"}]))
["X", "Y"]
iex> ExDatalog.Atom.variables(ExDatalog.Atom.new("fact", [:wildcard, {:const, 1}]))
[]