IO Operators

src/Debug.kt

@@ -1,3 +0,0 @@
-data object Debug {
-    val on: Boolean = true
-}

src/Main.kt

@@ -1,98 +1,15 @@
-import better_parser.PrologParser
+import interpreter.FileLoader
-import better_parser.SimpleReplParser
+import io.Logger
-import interpreter.SourceFileReader
-import prolog.Answer
 import prolog.Program
-import prolog.ast.logic.Fact
+import prolog.ast.logic.Clause
-import prolog.ast.logic.Rule
+import repl.Repl
-import prolog.ast.terms.Atom
-import prolog.ast.terms.CompoundTerm
-import prolog.ast.terms.Variable
-import prolog.builtins.Conjunction
-
-fun help(): String {
-    println("Unknown command. Type 'h' for help.")
-    println("Commands:")
-    println("  ;   - find next solution")
-    println("  a   - abort")
-    println("  .   - end query")
-    println("  h   - help")
-    println("  exit - exit Prolog REPL")
-    return ""
-}
-
-fun say(message: String) {
-    println(message)
-}
-
-fun prompt(message: String): String {
-    print("$message ")
-    var input: String = readlnOrNull() ?: help()
-    while (input.isBlank()) {
-        input = readlnOrNull() ?: help()
-    }
-    return input
-}
-
-fun prettyResult(result: Answer): String {
-    result.fold(
-        onSuccess = {
-            val subs = result.getOrNull()!!
-            if (subs.isEmpty()) {
-                return "true."
-            }
-            return subs.entries.joinToString(", ") { "${it.key} = ${it.value}" }
-        },
-        onFailure = {
-            return "Failure: ${result.exceptionOrNull()!!}"
-        }
-    )
-}
-
-val knownCommands = setOf(";", "a", ".")
 
 fun main() {
-    SourceFileReader().readFile("tests/better_parser/resources/parent.pl")
+    // TODO Make this a command line argument
+    // Turn on debug mode
+    Logger.level = Logger.Level.DEBUG
 
-    val parser = SimpleReplParser(debug = false)
+    FileLoader().load("tests/parser/resources/parent.pl")
-
-    say("Prolog REPL. Type 'exit' to quit.")
-
-    while (true) {
-        val queryString = prompt("?-")
-
-        try {
-            val query = parser.parse(queryString)
-            val answers = query.satisfy(emptyMap())
-
-            if (answers.none()) {
-                say("false.")
-            } else {
-                val iterator = answers.iterator()
-
-                var previous = iterator.next()
-
-                while (iterator.hasNext()) {
-                    var command = prompt(prettyResult(previous))
-
-                    while (command !in knownCommands) {
-                        say("Unknown action: $command (h for help)")
-                        command = prompt("Action?")
-                    }
-
-                    when (command) {
-                        ";" -> previous = iterator.next()
-                        "a" -> break
-                        "." -> break
-                    }
-                }
-
-                say(prettyResult(previous))
-            }
-
-        } catch (e: Exception) {
-            println("Error: ${e.message}")
-        }
-    }
 
+    Repl().start()
 }

src/interpreter/FileLoader.kt

@@ -0,0 +1,39 @@
+package interpreter
+
+import io.Logger
+import parser.ScriptParser
+import prolog.Program
+import prolog.ast.logic.Clause
+
+class FileLoader {
+    private val parser = ScriptParser()
+
+    fun load(filePath: String): () -> Unit {
+        val input = readFile(filePath)
+
+        Logger.debug("Parsing content of $filePath")
+        val clauses: List<Clause> = parser.parse(input)
+
+        Program.load(clauses)
+
+        // TODO Pass next commands to execute
+        return {}
+    }
+
+    fun readFile(filePath: String): String {
+        try {
+            Logger.debug("Reading $filePath")
+            val file = java.io.File(filePath)
+
+            if (!file.exists()) {
+                Logger.error("File $filePath does not exist")
+                throw IllegalArgumentException("File not found: $filePath")
+            }
+
+            return file.readText()
+        } catch (e: Exception) {
+            Logger.error("Error reading file: $filePath")
+            throw RuntimeException("Error reading file: $filePath", e)
+        }
+    }
+}

src/interpreter/Preprocessor.kt

@@ -0,0 +1,4 @@
+package interpreter
+
+class Preprocessor {
+}

src/interpreter/SourceFileReader.kt

@@ -1,23 +0,0 @@
-package interpreter
-
-import better_parser.PrologParser
-
-class SourceFileReader {
-    private val parser = PrologParser()
-
-    fun readFile(filePath: String) {
-        return try {
-            val file = java.io.File(filePath)
-            if (!file.exists()) {
-                throw IllegalArgumentException("File not found: $filePath")
-            }
-
-            val content = file.readText()
-
-            // Parse the content using SimpleSourceParser
-            parser.parse(content)
-        } catch (e: Exception) {
-            throw RuntimeException("Error reading file: $filePath", e)
-        }
-    }
-}

src/io/IoHandler.kt

@@ -0,0 +1,10 @@
+package io
+
+interface IoHandler {
+    fun prompt(
+        message: String,
+        hint: () -> String = { "Please enter a valid input." }
+    ): String
+
+    fun say(message: String)
+}

src/io/Logger.kt

@@ -0,0 +1,24 @@
+package io
+
+object Logger {
+    enum class Level {
+        DEBUG, INFO, WARN, ERROR
+    }
+
+    val defaultLevel: Level = Level.WARN
+    var level: Level = defaultLevel
+
+    private val io: IoHandler = Terminal()
+
+    fun log(message: String, messageLevel: Level = defaultLevel) {
+        if (level <= messageLevel) {
+            val text = "$messageLevel: $message\n"
+            io.say(text)
+        }
+    }
+
+    fun debug(message: String) = log(message, Level.DEBUG)
+    fun info(message: String) = log(message, Level.INFO)
+    fun warn(message: String) = log(message, Level.WARN)
+    fun error(message: String) = log(message, Level.ERROR)
+}

src/io/Terminal.kt

@@ -0,0 +1,63 @@
+package io
+
+import java.io.BufferedReader
+import java.io.BufferedWriter
+import java.io.InputStream
+import java.io.OutputStream
+
+/**
+ * Handles input and output from a terminal.
+ */
+class Terminal(
+    inputStream: InputStream = System.`in`,
+    outputStream: OutputStream = System.`out`,
+    errorStream: OutputStream = System.err
+) : IoHandler {
+    val input: BufferedReader = inputStream.bufferedReader()
+    val output: BufferedWriter = outputStream.bufferedWriter()
+    val error: BufferedWriter = errorStream.bufferedWriter()
+
+    override fun prompt(
+        message: String,
+        hint: () -> String
+    ): String {
+        say("$message ")
+        var input: String = readLine()
+        while (input.isBlank()) {
+            say(hint(), error)
+            input = readLine()
+        }
+        return input
+    }
+
+    override fun say(message: String) {
+        output.write(message)
+        output.flush()
+    }
+
+    fun say(message: String, writer: BufferedWriter = output) {
+        writer.write(message)
+        writer.flush()
+    }
+
+    /**
+     * Reads a line from the input stream.
+     */
+    fun readLine(reader: BufferedReader = input): String {
+        val line = reader.readLine()
+        if (line == null) {
+            Logger.info("End of stream reached")
+            cleanup()
+        }
+        return line
+
+    }
+
+    fun cleanup() {
+        Logger.info("Closing terminal streams")
+        input.close()
+        output.close()
+        error.close()
+        System.exit(0)
+    }
+}

src/parser/ReplParser.kt

@@ -1,9 +1,12 @@
 package parser
 
+import com.github.h0tk3y.betterParse.grammar.Grammar
+import com.github.h0tk3y.betterParse.grammar.parseToEnd
+import parser.grammars.QueryGrammar
 import prolog.builtins.Query
 
-class ReplParser: Parser {
+class ReplParser : Parser {
-    override fun parse(input: String): Query {
+    private val grammar: Grammar<Query> = QueryGrammar() as Grammar<Query>
-        TODO("Not yet implemented")
+
-    }
+    override fun parse(input: String): Query = grammar.parseToEnd(input)
 }

src/parser/grammars/QueryGrammar.kt

@@ -0,0 +1,16 @@
+package parser.grammars
+
+import com.github.h0tk3y.betterParse.combinators.times
+import com.github.h0tk3y.betterParse.combinators.unaryMinus
+import com.github.h0tk3y.betterParse.combinators.use
+import com.github.h0tk3y.betterParse.parser.Parser
+import prolog.ast.logic.LogicOperand
+import prolog.builtins.Query
+
+class QueryGrammar : TermsGrammar() {
+    protected val query: Parser<Query> by (body * -dot) use {
+        Query(this as LogicOperand)
+    }
+
+    override val rootParser: Parser<Any> by query
+}

src/prolog/Program.kt

@@ -1,6 +1,6 @@
 package prolog
 
-import Debug
+import io.Logger
 import prolog.ast.logic.Clause
 import prolog.ast.logic.Predicate
 import prolog.ast.logic.Resolvent
@@ -16,13 +16,14 @@ object Program: Resolvent {
     var predicates: Map<Functor, Predicate> = emptyMap()
 
     init {
+        Logger.debug("Initializing ${this::class.java.simpleName}")
         setup()
+        Logger.debug("Initialization of ${this::class.java.simpleName} complete")
     }
 
     private fun setup() {
-        if (Debug.on) {
+        Logger.debug("Setting up ${this::class.java.simpleName}")
-            println("Setting up Prolog program...")
+
-        }
         // Initialize the program with built-in predicates
         load(listOf(
         ))
@@ -35,6 +36,7 @@ object Program: Resolvent {
     fun query(goal: Goal): Answers = solve(goal, emptyMap())
 
     override fun solve(goal: Goal, subs: Substitutions): Answers {
+        Logger.debug("Solving goal $goal")
         val functor = goal.functor
         // If the predicate does not exist, return false
         val predicate = predicates[functor] ?: return emptySequence()
@@ -57,6 +59,8 @@ object Program: Resolvent {
                 // If the predicate does not exist, create a new one
                 predicates += Pair(functor, Predicate(listOf(clause)))
             }
+
+            Logger.debug("Loaded clause $clause into predicate $functor")
         }
     }
 
@@ -74,6 +78,7 @@ object Program: Resolvent {
     }
 
     fun clear() {
+        Logger.debug("Clearing ${this::class.java.simpleName}")
         predicates = emptyMap()
         setup()
     }

src/prolog/ast/logic/Predicate.kt

@@ -29,7 +29,6 @@ class Predicate : Resolvent {
      */
     constructor(clauses: List<Clause>) {
         this.functor = clauses.first().functor
-
         require(clauses.all { it.functor == functor }) { "All clauses must have the same functor" }
         this.clauses = clauses.toMutableList()
     }
@@ -39,11 +38,6 @@ class Predicate : Resolvent {
      */
     fun add(clause: Clause) {
         require(clause.functor == functor) { "Clause functor does not match predicate functor" }
-
-        if (Debug.on) {
-            println("Adding clause $clause to predicate $functor")
-        }
-
         clauses.add(clause)
     }
 

src/prolog/ast/terms/Operator.kt

@@ -6,7 +6,7 @@ abstract class Operator(
     private val symbol: Atom,
     private val leftOperand: Operand? = null,
     private val rightOperand: Operand
-) : CompoundTerm(symbol, listOfNotNull(leftOperand, rightOperand)) {
+) : CompoundTerm(symbol, listOfNotNull(leftOperand, rightOperand)), Term {
     override fun toString(): String {
         return when (leftOperand) {
             null -> "${symbol.name} $rightOperand"

src/prolog/ast/terms/Structure.kt

@@ -22,4 +22,15 @@ open class Structure(val name: Atom, var arguments: List<Argument>) : Goal(), He
             else -> "${name.name}(${arguments.joinToString(", ")})"
         }
     }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is Structure) return false
+        if (functor != other.functor) return false
+        return arguments.zip(other.arguments).all { (a, b) -> a == b }
+    }
+
+    override fun hashCode(): Int {
+        return javaClass.hashCode()
+    }
 }

src/prolog/builtins/io.kt

@@ -1,5 +1,8 @@
 package prolog.builtins
 
+import io.Logger
+import io.Terminal
+import parser.ReplParser
 import prolog.Answers
 import prolog.Substitutions
 import prolog.ast.logic.Satisfiable
@@ -7,13 +10,60 @@ import prolog.ast.terms.Atom
 import prolog.ast.terms.Operator
 import prolog.ast.terms.Term
 import prolog.logic.applySubstitution
+import prolog.logic.unifyLazy
 
+/**
+ * Write [Term] to the current output, using brackets and operators where appropriate.
+ */
 class Write(private val term: Term) : Operator(Atom("write"), null, term), Satisfiable {
     override fun satisfy(subs: Substitutions): Answers {
         val t = applySubstitution(term, subs)
 
-        println(t.toString())
+        Terminal().say(t.toString())
 
         return sequenceOf(Result.success(emptyMap()))
     }
 }
+
+/**
+ * Write a newline character to the current output stream.
+ */
+object Nl : Atom("nl"), Satisfiable {
+    override fun satisfy(subs: Substitutions): Answers {
+        Terminal().say("\n")
+        return sequenceOf(Result.success(emptyMap()))
+    }
+}
+
+/**
+ * Read the next Prolog term from the current input stream and unify it with [Term].
+ *
+ * On reaching end-of-file, [Term] is unified with the [Atom] `end_of_file`.
+ */
+class Read(private val term: Term) : Operator(Atom("read"), null, term), Satisfiable {
+    private val io = Terminal()
+    private val parser = ReplParser()
+
+    private fun readTerm(): Term {
+        val input = io.readLine()
+        Logger.debug("Read input: $input")
+
+        return when (input) {
+            "end_of_file" -> Atom("end_of_file")
+            else -> {
+                val out = parser.parse(input).query
+                Logger.debug("Parsed input: $out")
+                out as? Term ?: throw IllegalArgumentException("Expected a term, but got: $out")
+            }
+        }
+    }
+
+    override fun satisfy(subs: Substitutions): Answers = sequence {
+        val t1 = applySubstitution(term, subs)
+
+        val t2 = readTerm()
+        Logger.debug("Read term: $t2")
+
+        yieldAll(unifyLazy(t1, t2, subs))
+    }
+}

src/prolog/builtins/other.kt

@@ -6,6 +6,6 @@ import prolog.ast.logic.LogicOperand
 import prolog.ast.terms.Atom
 import prolog.ast.logic.LogicOperator
 
-class Query(private val query: LogicOperand) : LogicOperator(Atom("?-"), null, query) {
+class Query(val query: LogicOperand) : LogicOperator(Atom("?-"), null, query) {
     override fun satisfy(subs: Substitutions): Answers = query.satisfy(subs)
 }

src/prolog/logic/unification.kt

@@ -14,21 +14,24 @@ import prolog.ast.arithmetic.Float
 // Apply substitutions to a term
 fun applySubstitution(term: Term, subs: Substitutions): Term = when {
     variable(term, emptyMap()) -> subs[(term as Variable)] ?: term
-    atomic(term, subs)   -> term
+    atomic(term, subs) -> term
     compound(term, subs) -> {
         val structure = term as Structure
         Structure(structure.name, structure.arguments.map { applySubstitution(it, subs) })
     }
+
     else -> term
 }
+
 //TODO Combine with the other applySubstitution function
 fun applySubstitution(expr: Expression, subs: Substitutions): Expression = when {
     variable(expr, subs) -> applySubstitution(expr as Term, subs) as Expression
-    atomic(expr, subs)   -> expr
+    atomic(expr, subs) -> expr
     expr is LogicOperator -> {
         expr.arguments = expr.arguments.map { applySubstitution(it, subs) }
         expr
     }
+
     else -> expr
 }
 
@@ -40,6 +43,7 @@ private fun occurs(variable: Variable, term: Term, subs: Substitutions): Boolean
         val structure = term as Structure
         structure.arguments.any { occurs(variable, it, subs) }
     }
+
     else -> false
 }
 
@@ -56,12 +60,14 @@ fun unifyLazy(term1: Term, term2: Term, subs: Substitutions): Answers = sequence
                 yield(Result.success(subs + (variable to t2)))
             }
         }
+
         variable(t2, subs) -> {
             val variable = t2 as Variable
             if (!occurs(variable, t1, subs)) {
                 yield(Result.success(subs + (variable to t1)))
             }
         }
+
         compound(t1, subs) && compound(t2, subs) -> {
             val structure1 = t1 as Structure
             val structure2 = t2 as Structure
@@ -75,14 +81,17 @@ fun unifyLazy(term1: Term, term2: Term, subs: Substitutions): Answers = sequence
                     }
                     // Combine the results of all unifications
                     val combinedResults = results.reduce { acc, result ->
-                        acc.flatMap { a -> result.map { b ->
+                        acc.flatMap { a ->
-                            if (a.isSuccess && b.isSuccess) a.getOrThrow() + b.getOrThrow() else emptyMap()
+                            result.map { b ->
-                        } }.map { Result.success(it) }
+                                if (a.isSuccess && b.isSuccess) a.getOrThrow() + b.getOrThrow() else emptyMap()
+                            }
+                        }.map { Result.success(it) }
                     }
                     yieldAll(combinedResults)
                 }
             }
         }
+
         else -> {}
     }
 }
@@ -122,37 +131,40 @@ fun compare(term1: Term, term2: Term, subs: Substitutions): Int {
     return when (t1) {
         is Variable -> {
             when (t2) {
-                is Variable  -> t1.name.compareTo(t2.name)
+                is Variable -> t1.name.compareTo(t2.name)
                 is Number -> -1
-                is Atom      -> -1
+                is Atom -> -1
                 is Structure -> -1
                 else -> throw IllegalArgumentException("Cannot compare $t1 with $t2")
             }
         }
+
         is Number -> {
             when (t2) {
-                is Variable  -> 1
+                is Variable -> 1
-                is Integer   -> (t1.value as Int).compareTo(t2.value)
+                is Integer -> (t1.value as Int).compareTo(t2.value)
-                is Float     -> (t1.value as kotlin.Float).compareTo(t2.value)
+                is Float -> (t1.value as kotlin.Float).compareTo(t2.value)
-                is Atom      -> -1
+                is Atom -> -1
                 is Structure -> -1
                 else -> throw IllegalArgumentException("Cannot compare $t1 with $t2")
             }
         }
+
         is Atom -> {
             when (t2) {
-                is Variable  -> 1
+                is Variable -> 1
                 is Number -> 1
-                is Atom      -> t1.name.compareTo(t2.name)
+                is Atom -> t1.name.compareTo(t2.name)
                 is Structure -> -1
                 else -> throw IllegalArgumentException("Cannot compare $t1 with $t2")
             }
         }
+
         is Structure -> {
             when (t2) {
                 is Variable -> 1
                 is Number -> 1
-                is Atom     -> 1
+                is Atom -> 1
                 is Structure -> {
                     val arityComparison = t1.arguments.size.compareTo(t2.arguments.size)
                     if (arityComparison != 0) return arityComparison
@@ -164,9 +176,11 @@ fun compare(term1: Term, term2: Term, subs: Substitutions): Int {
                     }
                     return 0
                 }
+
                 else -> throw IllegalArgumentException("Cannot compare $t1 with $t2")
             }
         }
+
         else -> throw IllegalArgumentException("Cannot compare $t1 with $t2")
     }
 }

src/repl/Repl.kt

@@ -1,4 +1,90 @@
 package repl
 
+import io.Logger
+import io.Terminal
+import parser.ReplParser
+import prolog.Answer
+import prolog.Answers
+
 class Repl {
+    private val io = Terminal()
+    private val parser = ReplParser()
+
+    fun start() {
+        io.say("Prolog REPL. Type '^D' to quit.\n")
+        while (true) {
+            try {
+                printAnswers(query())
+            } catch (e: Exception) {
+                Logger.error("Error parsing REPL: ${e.message}")
+            }
+        }
+    }
+
+    fun query(): Answers {
+        val queryString = io.prompt("?-", { "" })
+        val query = parser.parse(queryString)
+        return query.satisfy(emptyMap())
+    }
+
+    fun printAnswers(answers: Answers) {
+        val knownCommands = setOf(";", "a", ".", "h")
+
+        if (answers.none()) {
+            io.say("false.")
+        } else {
+            val iterator = answers.iterator()
+            var previous = iterator.next()
+            io.say(prettyPrint(previous))
+
+            while (iterator.hasNext()) {
+                var command = io.prompt("")
+
+                while (command !in knownCommands) {
+                    io.say("Unknown action: $command (h for help)\n")
+                    command = io.prompt("Action?")
+                }
+
+                when (command) {
+                    ";" -> previous = iterator.next()
+                    "a" -> return
+                    "." -> return
+                    "h" -> {
+                        help()
+                        io.say("Action?")
+                    }
+                }
+            }
+
+            io.say(prettyPrint(previous))
+        }
+
+        io.say("\n")
+    }
+
+    fun help(): String {
+        io.say("Commands:\n")
+        io.say("  ;   find next solution\n")
+        io.say("  a   abort\n")
+        io.say("  .   end query\n")
+        io.say("  h   help\n")
+        return ""
+    }
+
+    fun prettyPrint(result: Answer): String {
+        result.fold(
+            onSuccess = {
+                val subs = result.getOrNull()!!
+                if (subs.isEmpty()) {
+                    return "true."
+                }
+                return subs.entries.joinToString(",\n") { "${it.key} = ${it.value}" }
+            },
+            onFailure = {
+                val text = "Failure: ${it.message}"
+                Logger.warn(text)
+                return text
+            }
+        )
+    }
 }

tests/interpreter/SourceFileReaderTests.kt

@@ -12,8 +12,8 @@ class SourceFileReaderTests {
 
     @Test
     fun a() {
-        val inputFile = "tests/better_parser/resources/a.pl"
+        val inputFile = "tests/parser/resources/a.pl"
-        val reader = SourceFileReader()
+        val reader = FileLoader()
 
         reader.readFile(inputFile)
 
@@ -22,8 +22,8 @@ class SourceFileReaderTests {
 
     @Test
     fun foo() {
-        val inputFile = "tests/better_parser/resources/foo.pl"
+        val inputFile = "tests/parser/resources/foo.pl"
-        val reader = SourceFileReader()
+        val reader = FileLoader()
 
         reader.readFile(inputFile)
 

tests/parser/ScriptParserTests.kt

@@ -1,36 +0,0 @@
-package parser
-
-import org.junit.jupiter.api.Assertions.assertEquals
-import org.junit.jupiter.api.Assertions.assertInstanceOf
-import org.junit.jupiter.api.BeforeEach
-import org.junit.jupiter.api.Test
-import prolog.ast.logic.Fact
-import prolog.ast.terms.Atom
-import prolog.logic.equivalent
-import kotlin.test.assertTrue
-
-class ScriptParserTests {
-    private lateinit var parser: ScriptParser
-
-    @BeforeEach
-    fun setup() {
-        parser = ScriptParser()
-    }
-
-    @Test
-    fun `parse single atom`() {
-        val input = """
-            a.
-        """.trimIndent()
-
-        val result = parser.parse(input)
-        val expected = Fact(Atom("a"))
-
-        assertEquals(1, result.size, "Should return one result")
-        assertInstanceOf(Fact::class.java, result[0], "Result should be a fact")
-        assertTrue(
-            equivalent(expected.head, result[0].head, emptyMap()),
-            "Expected fact 'a'"
-        )
-    }
-}

tests/parser/resources/parent.pl

@@ -5,8 +5,3 @@ parent(john, jimmy).
 parent(mary, jimmy).
 father(X, Y) :- parent(X, Y), male(X).
 mother(X, Y) :- parent(X, Y), female(X).
-
-:- write(hello),
-   nl.
-
-:- write(hello2).

tests/prolog/builtins/IoOperatorsTests.kt

@@ -1,8 +1,10 @@
 package prolog.builtins
 
 import org.junit.jupiter.api.Assertions.assertEquals
+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
@@ -13,6 +15,7 @@ import java.io.ByteArrayOutputStream
 import java.io.PrintStream
 import prolog.ast.arithmetic.Integer
 import prolog.ast.terms.Variable
+import java.io.ByteArrayInputStream
 
 class IoOperatorsTests {
     private var outStream = ByteArrayOutputStream()
@@ -44,7 +47,7 @@ class IoOperatorsTests {
 
         assertEquals(1, result.size, "Should return one result")
         assertTrue(result[0].isSuccess, "Result should be successful")
-        assertEquals(name, outStream.toString().trim(), "Output should match the atom")
+        assertEquals(name, outStream.toString(), "Output should match the atom")
     }
 
     @Test
@@ -79,7 +82,86 @@ class IoOperatorsTests {
         assertEquals(1, result.size, "Should return one result")
         assertTrue(result[0].isSuccess, "Result should be successful")
 
-        val output = outStream.toString().trim()
+        val output = outStream.toString()
         assertTrue(output == expected1 || output == expected2, "Output should match the arithmetic expression")
     }
+
+    @Test
+    fun `write nl`() {
+        val nl = Nl
+
+        val result = nl.satisfy(emptyMap()).toList()
+
+        assertEquals(1, result.size, "Should return one result")
+        assertTrue(result[0].isSuccess, "Result should be successful")
+        assertTrue(outStream.toString().contains("\n"), "Output should contain a newline")
+    }
+
+    @Test
+    fun `read term`() {
+        val inputStream = ByteArrayInputStream("hello.".toByteArray())
+        System.setIn(inputStream)
+
+        val read = Read(Variable("X"))
+
+        val result = read.satisfy(emptyMap()).toList()
+
+        assertEquals(1, result.size, "Should return one result")
+        assertTrue(result[0].isSuccess, "Result should be successful")
+        val answer = result[0].getOrNull()!!
+        assertTrue(answer.containsKey(Variable("X")), "Result should be successful")
+        assertInstanceOf(Atom::class.java, answer[Variable("X")], "Output should be an atom")
+        assertEquals(Atom("hello"), answer[Variable("X")], "Output should match the read term")
+    }
+
+    @Test
+    fun `read between(1, 2, 3)`() {
+        val inputStream = ByteArrayInputStream("between(1, 2, 3).".toByteArray())
+        System.setIn(inputStream)
+
+        val read = Read(Variable("X"))
+
+        val result = read.satisfy(emptyMap()).toList()
+
+        assertEquals(1, result.size, "Should return one result")
+        assertTrue(result[0].isSuccess, "Result should be successful")
+        val answer = result[0].getOrNull()!!
+        assertTrue(answer.containsKey(Variable("X")), "Result should be successful")
+        assertInstanceOf(CompoundTerm::class.java, answer[Variable("X")], "Output should be a compound term")
+        assertEquals(
+            CompoundTerm(Atom("between"), listOf(Integer(1), Integer(2), Integer(3))),
+            answer[Variable("X")],
+            "Output should match the read term"
+        )
+    }
+
+    @Test
+    fun `read foo(a, X, b, Y, c, Z)`() {
+        val inputStream = ByteArrayInputStream("foo(A, x, B, y, C, z).".toByteArray())
+        System.setIn(inputStream)
+
+        val read = Read(CompoundTerm(Atom("foo"), listOf(
+            Atom("a"),
+            Variable("X"),
+            Atom("b"),
+            Variable("Y"),
+            Atom("c"),
+            Variable("Z")
+        )))
+
+        val result = read.satisfy(emptyMap()).toList()
+
+        assertEquals(1, result.size, "Should return one result")
+        assertTrue(result[0].isSuccess, "Result should be successful")
+
+        val answer = result[0].getOrNull()!!
+
+        assertTrue(answer.containsKey(Variable("X")), "Result should be successful")
+        assertTrue(answer.containsKey(Variable("Y")), "Result should be successful")
+        assertTrue(answer.containsKey(Variable("Z")), "Result should be successful")
+
+        assertEquals(Atom("x"), answer[Variable("X")], "Output should match the read term")
+        assertEquals(Atom("y"), answer[Variable("Y")], "Output should match the read term")
+        assertEquals(Atom("z"), answer[Variable("Z")], "Output should match the read term")
+    }
 }