chore: Naming conventions
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8 changed files with 8 additions and 10 deletions
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package prolog.logic
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import org.junit.jupiter.api.Assertions.*
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import org.junit.jupiter.api.Disabled
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import org.junit.jupiter.api.Test
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import prolog.Substitutions
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import prolog.ast.arithmetic.Integer
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import prolog.ast.terms.Atom
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import prolog.ast.terms.Structure
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import prolog.ast.terms.Variable
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import prolog.builtins.Add
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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.isSuccess, "Identical atoms should unify")
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assertEquals(0, result.getOrNull()!!.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.isSuccess, "Different atoms should not unify")
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}
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/**
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* ?- X = X.
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* true.
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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.isSuccess, "Identical variables should unify")
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assertEquals(0, result.getOrNull()!!.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.isSuccess, "Variable should unify with atom")
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assertEquals(1, result.getOrNull()!!.size, "There should be one substitution")
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assertEquals(atom, result.getOrNull()!![variable], "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.isSuccess)
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assertEquals(1, result.getOrNull()!!.size)
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assertEquals(variable2, result.getOrNull()!![variable1], "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.isSuccess, "Identical compound terms should unify")
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assertEquals(0, result.getOrNull()!!.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.isSuccess, "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.isSuccess, "Compound terms with different functors should not unify")
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}
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/**
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* ?- X = f(a, b).
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* X = f(a, b).
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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.isSuccess, "Variable should unify with compound term")
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val subs = result.getOrNull()!!
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assertEquals(1, subs.size, "There should be one substitution")
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assertTrue(subs.containsKey(variable), "Variable should be in the substitution map")
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assertTrue(
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equivalent(Structure(Atom("f"), listOf(Atom("a"), Atom("b"))), subs[variable]!!, subs),
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"Variable should be substituted with compound term"
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)
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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.isSuccess, "Compound term with variable should unify with part")
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val subs = result.getOrNull()!!
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assertEquals(1, subs.size, "There should be one substitution")
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assertTrue(subs.containsKey(variable), "Variable should be in the substitution map")
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val equivalence = equivalent(Atom("b"), subs[variable]!!, subs)
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assertTrue(equivalence, "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.isSuccess, "Compound terms with variable arguments should unify")
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val subs = result.getOrNull()!!
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assertEquals(1, subs.size, "There should be one substitution")
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assertTrue(subs.containsKey(variable1), "Variable 1 should be in the substitution map")
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assertEquals(variable2, subs[variable1], "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.isSuccess, "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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* Y = g(X).
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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.isSuccess, "Nested compound terms with variables should unify")
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val subs = result.getOrNull()!!
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assertEquals(1, subs.size, "There should be one substitution")
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assertTrue(subs.containsKey(variable2), "Variable 2 should be in the substitution map")
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assertTrue(
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equivalent(Structure(Atom("g"), listOf(Variable("X"))), subs[variable2]!!, subs),
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"Variable should be substituted with compound term"
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)
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}
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/**
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* ?- f(g(X), X) = f(Y, a).
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* X = a,
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* Y = g(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.isSuccess, "Compound terms with more variables should unify")
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val subs = result.getOrNull()!!
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assertEquals(2, subs.size, "There should be two substitutions")
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assertTrue(subs.containsKey(variable1), "Variable 1 should be in the substitution map")
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assertTrue(
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equivalent(Atom("a"), subs[variable1]!!, subs),
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"Variable 1 should be substituted with atom"
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)
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assertTrue(subs.containsKey(variable2), "Variable 2 should be in the substitution map")
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assertTrue(
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equivalent(Structure(Atom("g"), listOf(Atom("a"))), subs[variable2]!!, subs),
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"Variable 2 should be substituted with compound term"
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)
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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 = unifyLazy(variable1, structure2, emptyMap()).toList()
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assertEquals(1, result.size, "There should be one result")
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assertTrue(result[0].isSuccess, "Recursive unification should succeed")
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val subs = result[0].getOrNull()!!
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assertEquals(1, subs.size, "There should be one substitution")
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assertTrue(subs.containsKey(variable1), "Variable should be in the substitution map")
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assertEquals(structure2, subs[variable1], "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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* X = Y, Y = bar.
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*/
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@Disabled
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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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val map: Substitutions = mapOf(
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variable1 to atom,
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variable2 to atom
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)
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val result = unifyLazy(variable1, variable2, map).toList()
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assertEquals(1, result.size, "There should be one substitution")
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assertTrue(result[0].isSuccess, "Multiple unification should succeed")
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assertEquals(0, result[0].getOrNull()!!.size, "No (additional) 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.isSuccess, "Atom with different arity should not unify")
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}
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@Test
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fun identical_integers_unify() {
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val int1 = Integer(1)
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val int2 = Integer(1)
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val result = unify(int1, int2)
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assertTrue(result.isSuccess, "Identical integers should unify")
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assertEquals(0, result.getOrNull()!!.size, "No substitutions should be made")
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}
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@Test
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fun different_integers_do_not_unify() {
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val int1 = Integer(1)
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val int2 = Integer(2)
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val result = unify(int1, int2)
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assertFalse(result.isSuccess, "Different integers should not unify")
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}
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@Test
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fun `1 + 2 does not unify with 3`() {
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val expr1 = Add(Integer(1), Integer(2))
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val expr2 = Integer(3)
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val result = unify(expr1, expr2)
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assertFalse(result.isSuccess, "1 + 2 should not unify with 3")
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}
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}
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