ExDatalog.Atom (ExDatalog v0.2.0)

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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

Types

t()

Functions

arity(atom)

Returns the arity (number of terms) of the atom.

new(relation, terms)

Constructs a new atom for the given relation and terms.

valid?(arg1)

Returns true if the atom is structurally valid.

variables(atom)

Returns all variable names in the atom's terms.

Types

t()

@type t() :: %ExDatalog.Atom{relation: String.t(), terms: [ExDatalog.Term.t()]}

Functions

arity(atom)

@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

new(relation, terms)

@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]}

valid?(arg1)

@spec valid?(t()) :: boolean()

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

variables(atom)

@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}]))
[]