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tests/prolog/UnifyTest.kt
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246
tests/prolog/UnifyTest.kt
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package prolog
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import org.junit.jupiter.api.Assertions.*
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import org.junit.jupiter.api.Test
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import prolog.components.terms.Atom
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import prolog.components.terms.Structure
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import prolog.components.terms.Variable
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/*
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* Based on: https://en.wikipedia.org/wiki/Unification_%28computer_science%29#Examples_of_syntactic_unification_of_first-order_terms
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*/
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class UnifyTest {
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@Test
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fun identical_atoms_unify() {
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val atom1 = Atom("a")
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val atom2 = Atom("a")
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val result = unify(atom1, atom2)
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assertTrue(result.isPresent, "Identical atoms should unify")
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assertEquals(0, result.get().size, "No substitutions should be made")
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}
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@Test
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fun different_atoms_do_not_unify() {
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val atom1 = Atom("a")
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val atom2 = Atom("b")
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val result = unify(atom1, atom2)
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assertFalse(result.isPresent, "Different atoms should not unify")
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}
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@Test
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fun identical_variables_unify() {
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val variable1 = Variable("X")
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val variable2 = Variable("X")
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val result = unify(variable1, variable2)
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assertTrue(result.isPresent, "Identical variables should unify")
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assertEquals(0, result.get().size, "No substitutions should be made")
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}
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@Test
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fun variable_unifies_with_atom() {
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val variable = Variable("X")
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val atom = Atom("a")
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val result = unify(atom, variable)
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assertTrue(result.isPresent, "Variable should unify with atom")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(atom, variable.alias().get(), "Variable should be substituted with atom")
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}
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@Test
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fun variables_alias_when_unified() {
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val variable1 = Variable("X")
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val variable2 = Variable("Y")
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val result = unify(variable1, variable2)
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assertTrue(result.isPresent)
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assertEquals(1, result.get().size)
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assertEquals(variable2, variable1.alias().get(), "Variable 1 should alias to variable 2")
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}
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@Test
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fun identical_compound_terms_unify() {
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val structure1 = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val structure2 = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val result = unify(structure1, structure2)
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assertTrue(result.isPresent, "Identical compound terms should unify")
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assertEquals(0, result.get().size, "No substitutions should be made")
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}
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@Test
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fun compound_terms_with_different_arguments_do_not_unify() {
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val structure1 = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val structure2 = Structure(Atom("f"), listOf(Atom("a"), Atom("c")))
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val result = unify(structure1, structure2)
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assertFalse(result.isPresent, "Different compound terms should not unify")
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}
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@Test
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fun compound_terms_with_different_functors_do_not_unify() {
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val structure1 = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val structure2 = Structure(Atom("g"), listOf(Atom("a"), Atom("b")))
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val result = unify(structure1, structure2)
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assertFalse(result.isPresent, "Compound terms with different functors should not unify")
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}
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@Test
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fun variable_unifies_with_compound_term() {
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val variable = Variable("X")
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val structure = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val result = unify(variable, structure)
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assertTrue(result.isPresent, "Variable should unify with compound term")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(structure, variable.alias().get(), "Variable should be substituted with compound term")
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}
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@Test
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fun compound_term_with_variable_unifies_with_part() {
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val variable = Variable("X")
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val structure1 = Structure(Atom("f"), listOf(Atom("a"), variable))
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val structure2 = Structure(Atom("f"), listOf(Atom("a"), Atom("b")))
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val result = unify(structure1, structure2)
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assertTrue(result.isPresent, "Compound term with variable should unify with part")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(Atom("b"), variable.alias().get(), "Variable should be substituted with atom")
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}
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@Test
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fun compound_terms_with_variable_arguments_lists_alias_variables() {
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val variable1 = Variable("X")
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val variable2 = Variable("Y")
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val structure1 = Structure(Atom("f"), listOf(variable1))
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val structure2 = Structure(Atom("f"), listOf(variable2))
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val result = unify(structure1, structure2)
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assertTrue(result.isPresent, "Compound terms with variable arguments should unify")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(variable2, variable1.alias().get(), "Variable 1 should alias to variable 2")
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}
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/**
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* f(X) = f(Y, Z)
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*/
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@Test
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fun compound_terms_with_different_arity_do_not_unify() {
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val structure1 = Structure(Atom("f"), listOf(Variable("X")))
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val structure2 = Structure(Atom("f"), listOf(Variable("Y"), Variable("Z")))
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val result = unify(structure1, structure2)
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assertFalse(result.isPresent, "Compound terms with different arity should not unify")
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}
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/**
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* f(g(X)) = f(Y)
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*/
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@Test
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fun nested_compound_terms_with_variables_unify() {
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val variable2 = Variable("Y")
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val structure1 = Structure(Atom("f"), listOf(Structure(Atom("g"), listOf(Variable("X")))))
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val structure2 = Structure(Atom("f"), listOf(variable2))
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val result = unify(structure1, structure2)
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assertTrue(result.isPresent, "Nested compound terms with variables should unify")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(Structure(Atom("g"), listOf(Variable("X"))), variable2.alias().get(), "Variable should be substituted with compound term")
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}
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/**
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* f(g(X), X) = f(Y, a)
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*/
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@Test
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fun compound_terms_with_more_variables() {
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val variable1 = Variable("X")
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val variable2 = Variable("Y")
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val structure1 = Structure(Atom("f"), listOf(Structure(Atom("g"), listOf(variable1)), variable1))
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val structure2 = Structure(Atom("f"), listOf(variable2, Atom("a")))
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val result = unify(structure1, structure2)
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assertTrue(result.isPresent, "Compound terms with more variables should unify")
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assertEquals(2, result.get().size, "There should be two substitutions")
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assertEquals(Atom("a"), variable1.alias().get(), "Variable 1 should be substituted with atom")
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assertEquals(Structure(Atom("g"), listOf(Atom("a"))), variable2.alias().get(), "Variable 2 should be substituted with compound term")
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}
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/**
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* ?- X = f(X).
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* X = f(f(X)).
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*/
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@Test
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fun recursive_unification() {
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val variable1 = Variable("X")
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val structure2 = Structure(Atom("f"), listOf(Variable("X")))
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val result = unify(variable1, structure2)
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assertTrue(result.isPresent, "Recursive unification should succeed")
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assertEquals(1, result.get().size, "There should be one substitution")
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assertEquals(structure2, variable1.alias().get(), "Variable should be substituted with compound term")
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}
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/**
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* ?- X = bar, Y = bar, X = Y.
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*/
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@Test
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fun multiple_unification() {
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val variable1 = Variable("X")
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val variable2 = Variable("Y")
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val atom = Atom("bar")
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variable1.bind(atom)
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variable2.bind(atom)
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val result = unify(variable1, variable2)
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assertTrue(result.isPresent, "Multiple unification should succeed")
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assertEquals(0, result.get().size, "No substitutions should be made")
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}
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/**
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* ?- a = a().
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* false.
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*/
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@Test
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fun atom_with_different_arity() {
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val atom1 = Atom("a")
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val structure2 = Structure(Atom("a"), emptyList())
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val result = unify(atom1, structure2)
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assertFalse(result.isPresent, "Atom with different arity should not unify")
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}
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@Test
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fun temp() {
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val atom1 = Atom("a")
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val atom2 = Atom("a")
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val result = unify(atom1, atom2)
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assertTrue(result.isPresent, "Identical atoms should unify")
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}
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}
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