Checkpoint

examples/scratchpad.pl

@@ -21,3 +21,7 @@ main :-
     write("but "),
     did_not_get_an_a(Y),
     write(Y), write(" did not get an A, "), fail; write("unfortunately."), nl.
+
+:- initialization(main).
+main :- write('gpl zegt: '), groet(wereld), nl.
+groet(X) :- write(dag(X)).

src/interpreter/Preprocessor.kt

@@ -66,6 +66,14 @@ open class Preprocessor {
                 when {
                     // TODO Remove hardcoding by storing the functors as constants in operators?
                     // Logic
+                    term.functor == "=/2" -> {
+                        Unify(args[0], args[1])
+                    }
+
+                    term.functor == "\\=/2" -> {
+                        NotUnify(args[0], args[1])
+                    }
+
                     term.functor == ",/2" -> {
                         Conjunction(args[0] as LogicOperand, args[1] as LogicOperand)
                     }
@@ -92,14 +100,6 @@ open class Preprocessor {
 
                     // Arithmetic
 
-                    term.functor == "=/2" && args.all { it is Expression } -> {
-                        Unify(args[0] as Expression, args[1] as Expression)
-                    }
-
-                    term.functor == "\\=/2" && args.all { it is Expression } -> {
-                        NotUnify(args[0] as Expression, args[1] as Expression)
-                    }
-
                     term.functor == "-/1" && args.all { it is Expression } -> {
                         Negate(args[0] as Expression)
                     }

src/parser/grammars/TermsGrammar.kt

@@ -7,6 +7,32 @@ import prolog.ast.arithmetic.Float
 import prolog.ast.arithmetic.Integer
 import prolog.ast.terms.*
 
+/**
+ * Precedence is based on the following table:
+ *
+ * | Precedence | Type | Operators                                                                                     |
+ * |------------|------|-----------------------------------------------------------------------------------------------|
+ * | 1200       | xfx  | --\>, :-, =\>, ==\>                                                                          |
+ * | 1200       | fx   | :-, ?-                                                                                       |
+ * | 1105       | xfy  | \|                                                                                           |
+ * | 1100       | xfy  | ;                                                                                           |
+ * | 1050       | xfy  | -\>, \*-\>                                                                                   |
+ * | 1000       | xfy  | ,                                                                                           |
+ * | 990        | xfx  | :=                                                                                          |
+ * | 900        | fy   | \\+                                                                                         |
+ * | 700        | xfx  | \<, =, =.., =:=, =\<, ==, =\\=, \>, \>=, \\=, \\==, as, is, \>:\<, :\<                      |
+ * | 600        | xfy  | :                                                                                           |
+ * | 500        | yfx  | +, -, /\\, \\/, xor                                                                          |
+ * | 500        | fx   | ?                                                                                           |
+ * | 400        | yfx  | \*, /, //, div, rdiv, \<\<, \>\>, mod, rem                                                   |
+ * | 200        | xfx  | \*\*                                                                                        |
+ * | 200        | xfy  | ^                                                                                           |
+ * | 200        | fy   | +, -, \\                                                                                     |
+ * | 100        | yfx  | .                                                                                           |
+ * | 1          | fx   | $                                                                                           |
+ *
+ * @see [SWI-Prolog Predicate op/3](https://www.swi-prolog.org/pldoc/man?predicate=op/3)
+ */
 open class TermsGrammar : Tokens() {
 
     // Basic named terms
@@ -19,7 +45,7 @@ open class TermsGrammar : Tokens() {
             ) use { Atom(text.substring(1, text.length - 1)) }
     protected val atom: Parser<Atom> by (quotedAtom or simpleAtom)
     protected val compound: Parser<Structure> by (atom * -leftParenthesis * separated(
-        parser(::term),
+        parser(::termNoConjunction),
         comma,
         acceptZero = true
     ) * -rightParenthesis) use {
@@ -30,51 +56,57 @@ open class TermsGrammar : Tokens() {
     protected val int: Parser<Integer> by integerToken use { Integer(text.toInt()) }
     protected val float: Parser<Float> by floatToken use { Float(text.toFloat()) }
 
-    // Operators
+    // Base terms (atoms, compounds, variables, numbers)
-    protected val ops: Parser<String> by (dummy
+    protected val baseTerm: Parser<Term> by (dummy
-            // Logic
+            or (-leftParenthesis * parser(::term) * -rightParenthesis)
-            or comma
-            or semicolon
-            // Arithmetic
-            or plus
-            or equals
-            or notEquals
-            ) use { this.text }
-    protected val simpleOperand: Parser<Operand> by (dummy
-            // Logic
             or compound
             or atom
             or variable
-            // Arithmetic
-            or int
             or float
+            or int
             )
-    protected val operand: Parser<Operand> by (dummy
+
-        or parser(::operator)
+    // Level 200 - prefix operators (+, -, \)
-        or simpleOperand
+    protected val op200: Parser<CompoundTerm> by ((plus or minus) * parser(::term200)) use {
-    )
+        CompoundTerm(Atom(t1.text), listOf(t2))
-    protected val operator: Parser<CompoundTerm> by (simpleOperand * ops * operand) use {
+    }
-        CompoundTerm(Atom(t2), listOf(t1, t3))
+    protected val term200: Parser<Term> by (op200 or baseTerm)
+
+    // Level 400 - multiplication, division
+    protected val op400: Parser<String> by (multiply or divide) use { text }
+    protected val term400: Parser<Term> by (term200 * zeroOrMore(op400 * term200)) use {
+        t2.fold(t1) { acc, (op, term) -> CompoundTerm(Atom(op), listOf(acc, term)) }
     }
 
-    // Parts
+    // Level 500 - addition, subtraction
-    protected val head: Parser<Head> by (dummy
+    protected val op500: Parser<String> by (plus or minus) use { text }
-            or compound
+    protected val term500: Parser<Term> by (term400 * zeroOrMore(op500 * term400)) use {
-            or atom
+        t2.fold(t1) { acc, (op, term) -> CompoundTerm(Atom(op), listOf(acc, term)) }
-            )
+    }
-    protected val body: Parser<Body> by (dummy
-            or operator
-            or head
-            or variable
-            ) use { this as Body }
 
-    protected val term: Parser<Term> by (dummy
+    // Level 700 - comparison operators
-            or float
+    protected val op700: Parser<String> by (equals or notEquals) use { text }
-            or int
+    protected val term700: Parser<Term> by (term500 * optional(op700 * term500)) use {
-            or variable
+        if (t2 == null) t1 else CompoundTerm(Atom(t2!!.t1), listOf(t1, t2!!.t2))
-            or compound
+    }
-            or atom
+
-            )
+    // Level 1000 - conjunction (,)
+    protected val term1000: Parser<Term> by (term700 * zeroOrMore(comma * term700)) use {
+        t2.fold(t1) { acc, (_, term) -> CompoundTerm(Atom(","), listOf(acc, term)) }
+    }
+
+    // Level 1100 - disjunction (;)
+    protected val term1100: Parser<Term> by (term1000 * zeroOrMore(semicolon * term1000)) use {
+        t2.fold(t1) { acc, (_, term) -> CompoundTerm(Atom(";"), listOf(acc, term)) }
+    }
+
+    // Term - highest level expression
+    protected val term: Parser<Term> by term1100
+    protected val termNoConjunction: Parser<Term> by term700
+
+    // Parts for clauses
+    protected val head: Parser<Head> by (compound or atom)
+    protected val body: Parser<Body> by term use { this as Body }
 
     override val rootParser: Parser<Any> by term
-}
+}

src/parser/grammars/Tokens.kt

@@ -25,6 +25,9 @@ abstract class Tokens : Grammar<Any>() {
     protected val equals: Token by literalToken("=")
     protected val notEquals: Token by literalToken("\\=")
     protected val plus: Token by literalToken("+")
+    protected val minus: Token by literalToken("-")
+    protected val multiply: Token by literalToken("*")
+    protected val divide: Token by literalToken("/")
     protected val dot by literalToken(".")
 
     // Ignored tokens

src/prolog/Program.kt

@@ -48,4 +48,10 @@ object Program : Resolvent {
 
         correspondingDBs.forEach { it.clear() }
     }
+
+    fun reset() {
+        clear()
+        variableRenamingStart = 0
+        storeNewLine = false
+    }
 }

src/prolog/ast/arithmetic/Integer.kt

@@ -1,11 +1,15 @@
 package prolog.ast.arithmetic
 
+import prolog.Answers
 import prolog.Substitutions
+import prolog.ast.logic.LogicOperand
 
-data class Integer(override val value: Int) : Number {
+data class Integer(override val value: Int) : Number, LogicOperand() {
     // Integers are already evaluated
     override fun simplify(subs: Substitutions): Simplification = Simplification(this, this)
 
+    override fun satisfy(subs: Substitutions): Answers = sequenceOf(Result.success(emptyMap()))
+
     override fun toString(): String = value.toString()
 
     override operator fun plus(other: Number): Number = when (other) {

src/prolog/ast/logic/Clause.kt

@@ -8,6 +8,7 @@ import prolog.builtins.True
 import prolog.flags.AppliedCut
 import prolog.logic.applySubstitution
 import prolog.logic.numbervars
+import prolog.logic.occurs
 import prolog.logic.unifyLazy
 
 /**
@@ -46,7 +47,7 @@ abstract class Clause(val head: Head, val body: Body) : Resolvent {
                                 .mapValues { reverse[it.value] ?: it.value }
                             result = result.map { it.key to applySubstitution(it.value, result) }
                                 .toMap()
-                                .filterNot { it.key in renamed.keys }
+                                .filterNot { it.key in renamed.keys && !occurs(it.key as Variable, goal, emptyMap())}
                             yield(Result.success(result))
                         },
                         onFailure = { error ->

src/prolog/ast/terms/Variable.kt

@@ -4,8 +4,9 @@ import prolog.Answers
 import prolog.Substitutions
 import prolog.ast.arithmetic.Expression
 import prolog.ast.arithmetic.Simplification
+import prolog.ast.logic.LogicOperand
 
-data class Variable(val name: String) : Term, Body, Expression {
+data class Variable(val name: String) : Term, Body, Expression, LogicOperand() {
     override fun simplify(subs: Substitutions): Simplification {
         // If the variable is bound, return the value of the binding
         // If the variable is not bound, return the variable itself

src/prolog/builtins/io.kt

@@ -18,7 +18,12 @@ import prolog.logic.unifyLazy
  */
 class Write(private val term: Term) : Operator(Atom("write"), null, term), Satisfiable {
     override fun satisfy(subs: Substitutions): Answers {
-        val t = applySubstitution(term, subs)
+        var t = term
+        var temp = applySubstitution(t, subs)
+        while (t != temp) {
+            t = temp
+            temp = applySubstitution(t, subs)
+        }
 
         Terminal().say(t.toString())
 

tests/compare.sh

@@ -2,11 +2,13 @@
 
 # This script is expected to be run from the root of the project.
 
+WATCH_ALONG=0
+
 # Paths to the two implementations
 GPL="src/gpl"
 SPL="swipl"
 
-GPL_FLAGS=("--debug")
+GPL_FLAGS=("--error")
 SPL_FLAGS=("--quiet" "-t" "'true'")
 
 # Directory containing test files
@@ -14,7 +16,11 @@ TEST_DIR="examples"
 
 # Temporary files for storing outputs
 GPL_OUT=$(mktemp)
+GPL_ERR=$(mktemp)
 SPL_OUT=$(mktemp)
+SPL_ERR=$(mktemp)
+
+touch "$GPL_OUT" "$GPL_ERR" "$SPL_OUT" "$SPL_ERR"
 
 # Flag to track if all tests pass
 PASSED=0
@@ -22,27 +28,43 @@ FAILED=0
 
 # Iterate over all test files in the test directory
 #for TESTFILE in $(find ${TEST_DIR} -type f); do
-files=("examples/program.pl" "examples/basics/disjunction.pl" "examples/basics/fraternity.pl")
+files=(
+"examples/program.pl"
+"examples/basics/disjunction.pl"
+"examples/basics/fraternity.pl"
+"examples/basics/unification.pl"
+"examples/basics/write.pl"
+)
 for TESTFILE in "${files[@]}"; do
     # Run both programs with the test file
-    "${SPL}" "${SPL_FLAGS[@]}" "$TESTFILE" > "${SPL_OUT}" 2>&1
+    "${SPL}" "${SPL_FLAGS[@]}" "$TESTFILE" > "${SPL_OUT}" 2> "${SPL_ERR}"
-    "${GPL}" "${GPL_FLAGS[@]}" -s "$TESTFILE" > "${GPL_OUT}" 2>&1
+    "${GPL}" "${GPL_FLAGS[@]}" -s "$TESTFILE" > "${GPL_OUT}" 2> "${GPL_ERR}"
 
     # Compare the outputs
-    if diff -q "$SPL_OUT" "$GPL_OUT" > /dev/null; then
+    was_different="$(
-        PASSED=$((PASSED + 1))
+        diff -q "$SPL_OUT" "$GPL_OUT" > /dev/null
-    else
+        echo $?
-        echo "Test failed! Outputs differ for $TESTFILE"
+    )"
-        printf "\nTest:\n%s\n" "$(cat "$TESTFILE")"
+    if [[ "${was_different}" -ne 0 || "${WATCH_ALONG}" -eq 1 ]]; then
-        printf "\nExpected:\n%s\n" "$(cat "$SPL_OUT")"
+        if [ "${was_different}" -ne 0 ]; then
-        printf "\nGot:\n%s\n" "$(cat "$GPL_OUT")"
+            message="TEST FAILED"
+        fi
+        printf "%s for %s\n" "${message:="Result"}" "${TESTFILE}"
+        printf "\nTest:\n%s\n" "$(cat "${TESTFILE}")"
+        printf "\nExpected:\n%s\n" "$(cat "${SPL_OUT}" && cat "${SPL_ERR}")"
+        printf "\nGot:\n%s\n" "$(cat "${GPL_OUT}" && cat "${GPL_ERR}")"
         echo "-----------------------------------------"
+    fi
+
+    if [ "${was_different}" -ne 0 ]; then
         FAILED=$((FAILED + 1))
+    else
+        PASSED=$((PASSED + 1))
     fi
 done
 
 # Clean up temporary files
-rm "$SPL_OUT" "$GPL_OUT"
+rm "$SPL_OUT" "$GPL_OUT" "$SPL_ERR" "$GPL_ERR"
 
 # Final result, summary
 if [ $FAILED -eq 0 ]; then

tests/e2e/Examples.kt

@@ -0,0 +1,46 @@
+package e2e
+
+import interpreter.FileLoader
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import prolog.Program
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
+
+class Examples {
+    private val loader = FileLoader()
+
+    @BeforeEach
+    fun setup() {
+        Program.reset()
+    }
+
+    @Test
+    fun fraternity() {
+        val inputFile = "examples/basics/fraternity.pl"
+
+        loader.load(inputFile)
+    }
+
+    @Test
+    fun unification() {
+        val inputFile = "examples/basics/unification.pl"
+
+        loader.load(inputFile)
+    }
+
+    @Test
+    fun write() {
+        val expected = "gpl zegt: dag(wereld)\n"
+
+        val outStream = ByteArrayOutputStream()
+        System.setOut(PrintStream(outStream))
+
+        val inputFile = "examples/basics/write.pl"
+
+        // Compare the stdio output with the expected output
+        loader.load(inputFile)
+        assertEquals(expected, outStream.toString())
+    }
+}

tests/e2e/myClass.kt

@@ -1,4 +0,0 @@
-package e2e
-
-class myClass {
-}

tests/parser/OperatorParserTests.kt

@@ -1,5 +1,6 @@
 package parser
 
+import com.github.h0tk3y.betterParse.combinators.use
 import com.github.h0tk3y.betterParse.grammar.Grammar
 import com.github.h0tk3y.betterParse.grammar.parseToEnd
 import com.github.h0tk3y.betterParse.parser.Parser
@@ -13,7 +14,7 @@ import prolog.ast.terms.Structure
 
 class OperatorParserTests {
     class OperatorParser: TermsGrammar() {
-        override val rootParser: Parser<CompoundTerm> by operator
+        override val rootParser: Parser<CompoundTerm> by body use { this as CompoundTerm }
     }
 
     private var parser = OperatorParser() as Grammar<CompoundTerm>

tests/parser/grammars/LogicGrammarTests.kt

@@ -40,7 +40,7 @@ class LogicGrammarTests {
 
         assertEquals(1, result.size, "Expected 1 fact")
         assertTrue(result[0] is Fact, "Expected a fact")
-        assertEquals(input, "${result[0].toString()}.", "Expected fact to be '$input'")
+        assertEquals(input, "${result[0]}.", "Expected fact to be '$input'")
     }
 
     @ParameterizedTest
@@ -125,9 +125,12 @@ class LogicGrammarTests {
 
         assertEquals(1, result.size, "Expected 1 rule")
         val rule = result[0] as Rule
-        assertInstanceOf(CompoundTerm::class.java, rule.body, "Expected body to be a conjunction")
+        assertEquals("guest/2", rule.head.functor, "Expected functor 'guest/2'")
-        val conjunction = rule.body as CompoundTerm
+        assertEquals(",/2", (rule.body as CompoundTerm).functor, "Expected functor ',/2'")
-        assertEquals("invited/2", (conjunction.arguments[0] as CompoundTerm).functor, "Expected functor 'invited/2'")
+        val l1 = (rule.body as CompoundTerm).arguments[0] as CompoundTerm
+        assertEquals(",/2", l1.functor, "Expected functor ',/2'")
+        val l2 = l1.arguments[0] as CompoundTerm
+        assertEquals("invited/2", l2.functor, "Expected functor 'invited/2'")
     }
 
     @Test

tests/parser/grammars/TermsGrammarTests.kt

@@ -2,10 +2,11 @@ package parser.grammars
 
 import com.github.h0tk3y.betterParse.grammar.Grammar
 import com.github.h0tk3y.betterParse.grammar.parseToEnd
-import com.github.h0tk3y.betterParse.parser.Parser
 import org.junit.jupiter.api.Assertions
 import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Nested
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertDoesNotThrow
 import org.junit.jupiter.params.ParameterizedTest
@@ -17,7 +18,6 @@ import prolog.ast.terms.Structure
 import prolog.ast.terms.Term
 import prolog.ast.terms.Variable
 import prolog.logic.equivalent
-import kotlin.test.assertEquals
 
 class TermsGrammarTests {
     private lateinit var parser: Grammar<Term>
@@ -32,7 +32,7 @@ class TermsGrammarTests {
     fun `parse atom`(name: String) {
         val result = parser.parseToEnd(name)
 
-        Assertions.assertEquals(Atom(name), result, "Expected atom '$name'")
+        assertEquals(Atom(name), result, "Expected atom '$name'")
     }
 
     @ParameterizedTest
@@ -52,7 +52,7 @@ class TermsGrammarTests {
 
         val expected = input.substring(1, input.length - 1)
 
-        Assertions.assertEquals(Atom(expected), result, "Expected atom")
+        assertEquals(Atom(expected), result, "Expected atom")
     }
 
     @ParameterizedTest
@@ -60,7 +60,7 @@ class TermsGrammarTests {
     fun `parse variable`(name: String) {
         val result = parser.parseToEnd(name)
 
-        Assertions.assertEquals(Variable(name), result, "Expected atom '$name'")
+        assertEquals(Variable(name), result, "Expected atom '$name'")
     }
 
     @Test
@@ -69,10 +69,7 @@ class TermsGrammarTests {
 
         val result = parser.parseToEnd(input)
 
-        Assertions.assertTrue(
+        assertEquals(Structure(Atom("f"), emptyList()), result, "Expected atom 'f'")
-            equivalent(Structure(Atom("f"), emptyList()), result, emptyMap()),
-            "Expected atom 'f'"
-        )
     }
 
     @Test
@@ -81,10 +78,7 @@ class TermsGrammarTests {
 
         val result = parser.parseToEnd(input)
 
-        Assertions.assertTrue(
+        assertEquals(Structure(Atom("f"), listOf(Atom("a"))), result, "Expected atom 'f(a)'")
-            equivalent(Structure(Atom("f"), listOf(Atom("a"))), result, emptyMap()),
-            "Expected atom 'f(a)'"
-        )
     }
 
     @Test
@@ -93,8 +87,9 @@ class TermsGrammarTests {
 
         val result = parser.parseToEnd(input)
 
-        Assertions.assertTrue(
+        assertEquals(
-            equivalent(Structure(Atom("f"), listOf(Atom("a"), Atom("b"))), result, emptyMap()),
+            Structure(Atom("f"), listOf(Atom("a"), Atom("b"))),
+            result,
             "Expected atom 'f(a, b)'"
         )
     }
@@ -105,7 +100,7 @@ class TermsGrammarTests {
 
         val result = parser.parseToEnd(input)
 
-        Assertions.assertTrue(
+        assertTrue(
             equivalent(Structure(Atom("f"), listOf(Atom("a"), Variable("X"))), result, emptyMap()),
             "Expected atom 'f(a, X)'"
         )
@@ -179,4 +174,59 @@ class TermsGrammarTests {
     fun `parse unification`(input: String) {
         assertDoesNotThrow { parser.parseToEnd(input) }
     }
+
+    @Nested
+    class `Operator precedence` {
+        private lateinit var parser: Grammar<Term>
+
+        @BeforeEach
+        fun setup() {
+            parser = TermsGrammar() as Grammar<Term>
+        }
+
+        @Test
+        fun `parse addition and multiplication`() {
+            val input = "1 + 2 * 3"
+
+            val result = parser.parseToEnd(input)
+
+            assertEquals(
+                Structure(Atom("+"), listOf(Integer(1), Structure(Atom("*"), listOf(Integer(2), Integer(3))))),
+                result,
+                "Expected addition and multiplication"
+            )
+        }
+
+        @Test
+        fun `parse multiplication and addition`() {
+            val input = "1 * 2 + 3"
+
+            val result = parser.parseToEnd(input)
+
+            assertEquals(
+                Structure(Atom("+"), listOf(Structure(Atom("*"), listOf(Integer(1), Integer(2))), Integer(3))),
+                result,
+                "Expected multiplication and addition"
+            )
+        }
+
+        @Test
+        fun `complex expression`() {
+            val input = "1 + 2 * 3 - 4 / 5"
+
+            val result = parser.parseToEnd(input)
+
+            assertEquals(
+                Structure(
+                    Atom("-"),
+                    listOf(
+                        Structure(Atom("+"), listOf(Integer(1), Structure(Atom("*"), listOf(Integer(2), Integer(3))))),
+                        Structure(Atom("/"), listOf(Integer(4), Integer(5)))
+                    )
+                ),
+                result,
+                "Expected complex expression"
+            )
+        }
+    }
 }

tests/prolog/EvaluationTests.kt

@@ -390,5 +390,27 @@ class EvaluationTests {
             assertEquals(1, subs5.size, "Expected 1 substitution, especially without 'Person'")
             assertEquals(Atom("bob"), subs5[Variable("X")], "Expected bob")
         }
+
+        @Test
+        fun `likes_italian_food(Person)`() {
+            val result = Program.query(Structure(Atom("likes_italian_food"), listOf(Variable("Person")))).toList()
+
+            assertEquals(3, result.size, "Expected 3 results")
+
+            assertTrue(result[0].isSuccess, "Expected success")
+            val subs3 = result[0].getOrNull()!!
+            assertEquals(1, subs3.size, "Expected 1 substitution")
+            assertEquals(Atom("alice"), subs3[Variable("Person")], "Expected alice")
+
+            assertTrue(result[1].isSuccess, "Expected success")
+            val subs4 = result[1].getOrNull()!!
+            assertEquals(1, subs4.size, "Expected 1 substitution")
+            assertEquals(Atom("alice"), subs4[Variable("Person")], "Expected alice")
+
+            assertTrue(result[2].isSuccess, "Expected success")
+            val subs5 = result[2].getOrNull()!!
+            assertEquals(1, subs5.size, "Expected 1 substitution")
+            assertEquals(Atom("bob"), subs5[Variable("Person")], "Expected bob")
+        }
     }
 }

tests/prolog/builtins/IoOperatorsTests.kt

@@ -1,21 +1,18 @@
 package prolog.builtins
 
-import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.*
-import org.junit.jupiter.api.Assertions.assertInstanceOf
-import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.BeforeEach
-import org.junit.jupiter.api.Disabled
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.params.ParameterizedTest
 import org.junit.jupiter.params.provider.ValueSource
 import prolog.ast.arithmetic.Float
+import prolog.ast.arithmetic.Integer
 import prolog.ast.terms.Atom
 import prolog.ast.terms.CompoundTerm
-import java.io.ByteArrayOutputStream
-import java.io.PrintStream
-import prolog.ast.arithmetic.Integer
 import prolog.ast.terms.Variable
 import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
 
 class IoOperatorsTests {
     private var outStream = ByteArrayOutputStream()