diff --git a/core/src/commonMain/kotlin/world/phantasmal/core/PrimitiveExtensions.kt b/core/src/commonMain/kotlin/world/phantasmal/core/PrimitiveExtensions.kt
new file mode 100644
index 00000000..5b513d39
--- /dev/null
+++ b/core/src/commonMain/kotlin/world/phantasmal/core/PrimitiveExtensions.kt
@@ -0,0 +1,3 @@
+package world.phantasmal.core
+
+fun Char.isDigit(): Boolean = this in '0'..'9'
diff --git a/core/src/commonMain/kotlin/world/phantasmal/core/PwResult.kt b/core/src/commonMain/kotlin/world/phantasmal/core/PwResult.kt
index 3ace047e..b500b057 100644
--- a/core/src/commonMain/kotlin/world/phantasmal/core/PwResult.kt
+++ b/core/src/commonMain/kotlin/world/phantasmal/core/PwResult.kt
@@ -18,12 +18,17 @@ class Success<T>(val value: T, problems: List<Problem> = emptyList()) : PwResult
 
 class Failure(problems: List<Problem>) : PwResult<Nothing>(problems)
 
-class Problem(
+open class Problem(
     val severity: Severity,
     /**
      * Readable message meant for users.
      */
     val uiMessage: String,
+    /**
+     * Message meant for developers.
+     */
+    val message: String? = null,
+    val cause: Throwable? = null,
 )
 
 enum class Severity {
@@ -38,6 +43,22 @@ enum class Severity {
 class PwResultBuilder<T>(private val logger: KLogger) {
     private val problems: MutableList<Problem> = mutableListOf()
 
+    /**
+     * Add a problem to the problems list and log it with [logger].
+     */
+    fun addProblem(
+        problem: Problem,
+    ): PwResultBuilder<T> {
+        when (problem.severity) {
+            Severity.Info -> logger.info(problem.cause) { problem.message ?: problem.uiMessage }
+            Severity.Warning -> logger.warn(problem.cause) { problem.message ?: problem.uiMessage }
+            Severity.Error -> logger.error(problem.cause) { problem.message ?: problem.uiMessage }
+        }
+
+        problems.add(problem)
+        return this
+    }
+
     /**
      * Add a problem to the problems list and log it with [logger].
      */
@@ -46,16 +67,8 @@ class PwResultBuilder<T>(private val logger: KLogger) {
         uiMessage: String,
         message: String? = null,
         cause: Throwable? = null,
-    ): PwResultBuilder<T> {
-        when (severity) {
-            Severity.Info -> logger.info(cause) { message ?: uiMessage }
-            Severity.Warning -> logger.warn(cause) { message ?: uiMessage }
-            Severity.Error -> logger.error(cause) { message ?: uiMessage }
-        }
-
-        problems.add(Problem(severity, uiMessage))
-        return this
-    }
+    ): PwResultBuilder<T> =
+        addProblem(Problem(severity, uiMessage, message, cause))
 
     /**
      * Add the given result's problems.
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Assembly.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Assembly.kt
new file mode 100644
index 00000000..98601e11
--- /dev/null
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Assembly.kt
@@ -0,0 +1,716 @@
+package world.phantasmal.lib.assembly
+
+import mu.KotlinLogging
+import world.phantasmal.core.Problem
+import world.phantasmal.core.PwResult
+import world.phantasmal.core.PwResultBuilder
+import world.phantasmal.core.Severity
+import world.phantasmal.lib.buffer.Buffer
+
+private val logger = KotlinLogging.logger {}
+
+class AssemblyProblem(
+    severity: Severity,
+    uiMessage: String,
+    message: String? = null,
+    cause: Throwable? = null,
+    val lineNo: Int,
+    val col: Int,
+    val length: Int,
+) : Problem(severity, uiMessage, message, cause)
+
+class AssemblySettings(
+    val manualStack: Boolean,
+)
+
+fun assemble(
+    assembly: List<String>,
+    manualStack: Boolean = false,
+): PwResult<List<Segment>> {
+    logger.trace { "Assembly start." }
+
+    val result = Assembler(assembly, manualStack).assemble()
+
+    logger.trace {
+        val warnings = result.problems.count { it.severity == Severity.Warning }
+        val errors = result.problems.count { it.severity == Severity.Error }
+
+        "Assembly finished with $warnings warnings and $errors errors."
+    }
+
+    return result
+}
+
+private class Assembler(private val assembly: List<String>, private val manualStack: Boolean) {
+    private var lineNo = 1
+    private lateinit var tokens: MutableList<Token>
+    private var objectCode: MutableList<Segment> = mutableListOf()
+
+    /**
+     * The current segment.
+     */
+    private var segment: Segment? = null
+
+    /**
+     * Encountered labels.
+     */
+    private val labels: MutableSet<Int> = mutableSetOf()
+    private var section: SegmentType = SegmentType.Instructions
+    private var firstSectionMarker = true
+    private var prevLineHadLabel = false
+
+    private val result = PwResultBuilder<List<Segment>>(logger)
+
+    fun assemble(): PwResult<List<Segment>> {
+        // Tokenize and assemble line by line.
+        for (line in assembly) {
+            tokens = tokenizeLine(line)
+
+            if (tokens.isNotEmpty()) {
+                val token = tokens.removeFirst()
+                var hasLabel = false
+
+                when (token) {
+                    is LabelToken -> {
+                        parseLabel(token)
+                        hasLabel = true
+                    }
+                    is SectionToken,
+                    -> {
+                        parseSection(token)
+                    }
+                    is IntToken -> {
+                        if (section == SegmentType.Data) {
+                            parseBytes(token)
+                        } else {
+                            addUnexpectedTokenError(token)
+                        }
+                    }
+                    is StringToken -> {
+                        if (section == SegmentType.String) {
+                            parseString(token)
+                        } else {
+                            addUnexpectedTokenError(token)
+                        }
+                    }
+                    is IdentToken -> {
+                        if (section === SegmentType.Instructions) {
+                            parseInstruction(token)
+                        } else {
+                            addUnexpectedTokenError(token)
+                        }
+                    }
+                    is InvalidSectionToken -> {
+                        addError(token, "Invalid section type.")
+                    }
+                    is InvalidIdentToken -> {
+                        addError(token, "Invalid identifier.")
+                    }
+                    else -> {
+                        addUnexpectedTokenError(token)
+                    }
+                }
+
+                prevLineHadLabel = hasLabel
+            }
+
+            lineNo++
+        }
+
+        return result.success(objectCode)
+    }
+
+    private fun addInstruction(
+        opcode: Opcode,
+        args: List<Arg>,
+        stackArgs: List<Arg>,
+        token: Token?,
+        argTokens: List<Token>,
+        stackArgTokens: List<Token>,
+    ) {
+        when (val seg = segment) {
+            null -> {
+                // Unreachable code, technically valid.
+                segment = InstructionSegment(
+                    labels = mutableListOf(),
+                    instructions = mutableListOf(),
+                    srcLoc = SegmentSrcLoc()
+                )
+
+                objectCode.add(segment!!)
+            }
+
+            is InstructionSegment -> {
+                seg.instructions.add(
+                    Instruction(
+                        opcode,
+                        args,
+                        InstructionSrcLoc(
+                            mnemonic = token?.let {
+                                SrcLoc(lineNo, token.col, token.len)
+                            },
+                            args = argTokens.map {
+                                SrcLoc(lineNo, it.col, it.len)
+                            },
+                            stackArgs = stackArgTokens.mapIndexed { i, sat ->
+                                StackArgSrcLoc(lineNo, sat.col, sat.len, stackArgs[i].value)
+                            },
+                        )
+                    )
+                )
+            }
+
+            else -> {
+                logger.error { "Line $lineNo: Expected instructions segment." }
+            }
+        }
+    }
+
+    private fun addBytes(bytes: ByteArray) {
+        when (val seg = segment) {
+            null -> {
+                // Unaddressable data, technically valid.
+                segment = DataSegment(
+                    labels = mutableListOf(),
+                    data = Buffer.fromByteArray(bytes),
+                    srcLoc = SegmentSrcLoc()
+                )
+
+                objectCode.add(segment!!)
+            }
+
+            is DataSegment -> {
+                val oldSize = seg.data.size
+                seg.data.size += bytes.size.toUInt()
+
+                for (i in bytes.indices) {
+                    seg.data.setI8(i.toUInt() + oldSize, bytes[i])
+                }
+            }
+
+            else -> {
+                logger.error { "Line $lineNo: Expected data segment." }
+            }
+        }
+    }
+
+    private fun addString(str: String) {
+        when (val seg = segment) {
+            null -> {
+                // Unaddressable data, technically valid.
+                segment = StringSegment(
+                    labels = mutableListOf(),
+                    value = str,
+                    srcLoc = SegmentSrcLoc()
+                )
+
+                objectCode.add(segment!!)
+            }
+
+            is StringSegment -> {
+                seg.value += str
+            }
+
+            else -> {
+                logger.error { "Line $lineNo: Expected string segment." }
+            }
+        }
+    }
+
+    private fun addError(col: Int, length: Int, message: String) {
+        result.addProblem(
+            AssemblyProblem(
+                Severity.Error,
+                message,
+                lineNo = lineNo,
+                col = col,
+                length = length
+            )
+        )
+    }
+
+    private fun addError(token: Token, message: String) {
+        addError(token.col, token.len, message)
+    }
+
+    private fun addUnexpectedTokenError(token: Token) {
+        addError(token, "Unexpected token.")
+    }
+
+    private fun addWarning(token: Token, message: String) {
+        result.addProblem(
+            AssemblyProblem(
+                Severity.Warning,
+                message,
+                lineNo = lineNo,
+                col = token.col,
+                length = token.len
+            )
+        )
+    }
+
+    private fun parseLabel(token: LabelToken) {
+        val label = token.value
+
+        if (labels.add(label)) {
+            addError(token, "Duplicate label.")
+        }
+
+        val nextToken = tokens.removeFirstOrNull()
+
+        val srcLoc = SrcLoc(lineNo, token.col, token.len)
+
+        if (prevLineHadLabel) {
+            val segment = objectCode.last()
+            segment.labels.add(label)
+            segment.srcLoc.labels.add(srcLoc)
+        }
+
+        when (section) {
+            SegmentType.Instructions -> {
+                if (!prevLineHadLabel) {
+                    segment = InstructionSegment(
+                        labels = mutableListOf(label),
+                        instructions = mutableListOf(),
+                        srcLoc = SegmentSrcLoc(labels = mutableListOf(srcLoc)),
+                    )
+
+                    objectCode.add(segment!!)
+                }
+
+                if (nextToken != null) {
+                    if (nextToken is IdentToken) {
+                        parseInstruction(nextToken)
+                    } else {
+                        addError(nextToken, "Expected opcode mnemonic.")
+                    }
+                }
+            }
+
+            SegmentType.Data -> {
+                if (!prevLineHadLabel) {
+                    segment = DataSegment(
+                        labels = mutableListOf(label),
+                        data = Buffer.withCapacity(0u),
+                        srcLoc = SegmentSrcLoc(labels = mutableListOf(srcLoc)),
+                    )
+                    objectCode.add(segment!!)
+                }
+
+                if (nextToken != null) {
+                    if (nextToken is IntToken) {
+                        parseBytes(nextToken)
+                    } else {
+                        addError(nextToken, "Expected bytes.")
+                    }
+                }
+            }
+
+            SegmentType.String -> {
+                if (!prevLineHadLabel) {
+                    segment = StringSegment(
+                        labels = mutableListOf(label),
+                        value = "",
+                        srcLoc = SegmentSrcLoc(labels = mutableListOf(srcLoc)),
+                    )
+                    objectCode.add(segment!!)
+                }
+
+                if (nextToken != null) {
+                    if (nextToken is StringToken) {
+                        parseString(nextToken)
+                    } else {
+                        addError(nextToken, "Expected a string.")
+                    }
+                }
+            }
+        }
+    }
+
+    private fun parseSection(token: SectionToken) {
+        val section = when (token) {
+            is CodeSectionToken -> SegmentType.Instructions
+            is DataSectionToken -> SegmentType.Data
+            is StringSectionToken -> SegmentType.String
+        }
+
+        if (this.section == section && !firstSectionMarker) {
+            addWarning(token, "Unnecessary section marker.")
+        }
+
+        this.section = section
+        firstSectionMarker = false
+
+        tokens.removeFirstOrNull()?.let { nextToken ->
+            addUnexpectedTokenError(nextToken)
+        }
+    }
+
+    private fun parseInstruction(identToken: IdentToken) {
+        val opcode = mnemonicToOpcode(identToken.value)
+
+        if (opcode == null) {
+            addError(identToken, "Unknown instruction.")
+        } else {
+            val varargs = opcode.params.any {
+                it.type is ILabelVarType || it.type is RegRefVarType
+            }
+
+            val paramCount =
+                if (manualStack && opcode.stack == StackInteraction.Pop) 0
+                else opcode.params.size
+
+            val argCount = tokens.count { it !is ArgSeparatorToken }
+
+            val lastToken = tokens.lastOrNull()
+            val errorLength = lastToken?.let { it.col + it.len - identToken.col } ?: 0
+            // Inline arguments.
+            val insArgAndTokens = mutableListOf<Pair<Arg, Token>>()
+            // Stack arguments.
+            val stackArgAndTokens = mutableListOf<Pair<Arg, Token>>()
+
+            if (!varargs && argCount != paramCount) {
+                addError(
+                    identToken.col,
+                    errorLength,
+                    "Expected $paramCount argument ${if (paramCount == 1) "" else "s"}, got $argCount."
+                )
+
+                return
+            } else if (varargs && argCount < paramCount) {
+                addError(
+                    identToken.col,
+                    errorLength,
+                    "Expected at least $paramCount argument ${if (paramCount == 1) "" else "s"}, got $argCount.",
+                )
+
+                return
+            } else if (opcode.stack !== StackInteraction.Pop) {
+                // Inline arguments.
+                if (!parseArgs(opcode.params, insArgAndTokens, stack = false)) {
+                    return
+                }
+            } else {
+                if (!this.parseArgs(opcode.params, stackArgAndTokens, stack = true)) {
+                    return
+                }
+
+                for (i in opcode.params.indices) {
+                    val param = opcode.params[i]
+                    val argAndToken = stackArgAndTokens.getOrNull(i) ?: continue
+                    val (arg, argToken) = argAndToken
+
+                    if (argToken is RegisterToken) {
+                        if (param.type is RegTupRefType) {
+                            addInstruction(
+                                OP_ARG_PUSHB,
+                                listOf(arg),
+                                emptyList(),
+                                null,
+                                listOf(argToken),
+                                emptyList(),
+                            )
+                        } else {
+                            addInstruction(
+                                OP_ARG_PUSHR,
+                                listOf(arg),
+                                emptyList(),
+                                null,
+                                listOf(argToken),
+                                emptyList(),
+                            )
+                        }
+                    } else {
+                        when (param.type) {
+                            is ByteType,
+                            is RegRefType,
+                            is RegTupRefType,
+                            -> {
+                                addInstruction(
+                                    OP_ARG_PUSHB,
+                                    listOf(arg),
+                                    emptyList(),
+                                    null,
+                                    listOf(argToken),
+                                    emptyList(),
+                                )
+                            }
+
+                            is WordType,
+                            is LabelType,
+                            is ILabelType,
+                            is DLabelType,
+                            is SLabelType,
+                            -> {
+                                addInstruction(
+                                    OP_ARG_PUSHW,
+                                    listOf(arg),
+                                    emptyList(),
+                                    null,
+                                    listOf(argToken),
+                                    emptyList(),
+                                )
+                            }
+
+                            is DWordType -> {
+                                addInstruction(
+                                    OP_ARG_PUSHL,
+                                    listOf(arg),
+                                    emptyList(),
+                                    null,
+                                    listOf(argToken),
+                                    emptyList(),
+                                )
+                            }
+
+                            is FloatType -> {
+                                addInstruction(
+                                    OP_ARG_PUSHL,
+                                    listOf(Arg((arg.value as Float).toRawBits())),
+                                    emptyList(),
+                                    null,
+                                    listOf(argToken),
+                                    emptyList(),
+                                )
+                            }
+
+                            is StringType -> {
+                                addInstruction(
+                                    OP_ARG_PUSHS,
+                                    listOf(arg),
+                                    emptyList(),
+                                    null,
+                                    listOf(argToken),
+                                    emptyList(),
+                                )
+                            }
+
+                            else -> {
+                                logger.error {
+                                    "Line $lineNo: Type ${param.type::class} not implemented."
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            val (args, argTokens) = insArgAndTokens.unzip()
+            val (stackArgs, stackArgTokens) = stackArgAndTokens.unzip()
+
+            addInstruction(
+                opcode,
+                args,
+                stackArgs,
+                identToken,
+                argTokens,
+                stackArgTokens,
+            )
+        }
+    }
+
+    /**
+     * @returns true if arguments can be translated to object code, possibly after truncation. False otherwise.
+     */
+    private fun parseArgs(
+        params: List<Param>,
+        argAndTokens: MutableList<Pair<Arg, Token>>,
+        stack: Boolean,
+    ): Boolean {
+        var semiValid = true
+        var shouldBeArg = true
+        var paramI = 0
+
+        for (i in 0 until tokens.size) {
+            val token = tokens[i]
+            val param = params[paramI]
+
+            if (token is ArgSeparatorToken) {
+                if (shouldBeArg) {
+                    addError(token, "Expected an argument.")
+                } else if (
+                    param.type !is ILabelVarType &&
+                    param.type !is RegRefVarType
+                ) {
+                    paramI++
+                }
+
+                shouldBeArg = true
+            } else {
+                if (!shouldBeArg) {
+                    val prevToken = tokens[i - 1]
+                    val col = prevToken.col + prevToken.len
+
+                    addError(col, token.col - col, "Expected a comma.")
+                }
+
+                shouldBeArg = false
+
+                var match: Boolean
+
+                when (token) {
+                    is IntToken -> {
+                        when (param.type) {
+                            is ByteType -> {
+                                match = true
+                                parseInt(1, token, argAndTokens)
+                            }
+                            is WordType,
+                            is LabelType,
+                            is ILabelType,
+                            is DLabelType,
+                            is SLabelType,
+                            is ILabelVarType,
+                            -> {
+                                match = true
+                                parseInt(2, token, argAndTokens)
+                            }
+                            is DWordType -> {
+                                match = true
+                                parseInt(4, token, argAndTokens)
+                            }
+                            is FloatType -> {
+                                match = true
+                                argAndTokens.add(Pair(Arg(token.value), token))
+                            }
+                            else -> {
+                                match = false
+                            }
+                        }
+                    }
+
+                    is FloatToken -> {
+                        match = param.type == FloatType
+
+                        if (match) {
+                            argAndTokens.add(Pair(Arg(token.value), token))
+                        }
+                    }
+
+                    is RegisterToken -> {
+                        match = stack ||
+                                param.type is RegRefType ||
+                                param.type is RegRefVarType ||
+                                param.type is RegTupRefType
+
+                        parseRegister(token, argAndTokens)
+                    }
+
+                    is StringToken -> {
+                        match = param.type is StringType
+
+                        if (match) {
+                            argAndTokens.add(Pair(Arg(token.value), token))
+                        }
+                    }
+
+                    else -> {
+                        match = false
+                    }
+                }
+
+                if (!match) {
+                    semiValid = false
+
+                    val typeStr: String? = when (param.type) {
+                        is ByteType -> "an 8-bit integer"
+                        is WordType -> "a 16-bit integer"
+                        is DWordType -> "a 32-bit integer"
+                        is FloatType -> "a float"
+                        is LabelType -> "a label"
+
+                        is ILabelType,
+                        is ILabelVarType,
+                        -> "an instruction label"
+
+                        is DLabelType -> "a data label"
+                        is SLabelType -> "a string label"
+                        is StringType -> "a string"
+
+                        is RegRefType,
+                        is RegRefVarType,
+                        is RegTupRefType,
+                        -> "a register reference"
+
+                        else -> null
+                    }
+
+                    addError(
+                        token,
+                        if (typeStr == null) "Unexpected token." else "Expected ${typeStr}."
+                    )
+                }
+            }
+        }
+
+        tokens.clear()
+        return semiValid
+    }
+
+    private fun parseInt(size: Int, token: IntToken, argAndTokens: MutableList<Pair<Arg, Token>>) {
+        val value = token.value
+        val bitSize = 8 * size
+        // Minimum of the signed version of this integer type.
+        val minValue = -(1 shl (bitSize - 1))
+        // Maximum of the unsigned version of this integer type.
+        val maxValue = (1 shl (bitSize)) - 1
+
+        when {
+            value < minValue -> {
+                addError(token, "${bitSize}-Bit integer can't be less than ${minValue}.")
+            }
+            value > maxValue -> {
+                addError(token, "${bitSize}-Bit integer can't be greater than ${maxValue}.")
+            }
+            else -> {
+                argAndTokens.add(Pair(Arg(value), token))
+            }
+        }
+    }
+
+    private fun parseRegister(token: RegisterToken, argAndTokens: MutableList<Pair<Arg, Token>>) {
+        val value = token.value
+
+        if (value > 255) {
+            addError(token, "Invalid register reference, expected r0-r255.")
+        } else {
+            argAndTokens.add(Pair(Arg(value), token))
+        }
+    }
+
+    private fun parseBytes(firstToken: IntToken) {
+        val bytes = mutableListOf<Byte>()
+        var token: Token = firstToken
+        var i = 0
+
+        while (token is IntToken) {
+            if (token.value < 0) {
+                addError(token, "Unsigned 8-bit integer can't be less than 0.")
+            } else if (token.value > 255) {
+                addError(token, "Unsigned 8-bit integer can't be greater than 255.")
+            }
+
+            bytes.add(token.value.toByte())
+
+            if (i < tokens.size) {
+                token = tokens[i++]
+            } else {
+                break
+            }
+        }
+
+        if (i < tokens.size) {
+            addError(token, "Expected an unsigned 8-bit integer.")
+        }
+
+        addBytes(bytes.toByteArray())
+    }
+
+    private fun parseString(token: StringToken) {
+        tokens.removeFirstOrNull()?.let { nextToken ->
+            addUnexpectedTokenError(nextToken)
+        }
+
+        addString(token.value.replace("\n", "<cr>"))
+    }
+}
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/AssemblyTokenization.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/AssemblyTokenization.kt
new file mode 100644
index 00000000..0826ffc7
--- /dev/null
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/AssemblyTokenization.kt
@@ -0,0 +1,353 @@
+package world.phantasmal.lib.assembly
+
+import world.phantasmal.core.isDigit
+
+private val HEX_INT_REGEX = Regex("""^0x[\da-fA-F]+$""")
+private val FLOAT_REGEX = Regex("""^-?\d+(\.\d+)?(e-?\d+)?$""")
+private val IDENT_REGEX = Regex("""^[a-z][a-z0-9_=<>!]*$""")
+
+sealed class Token(
+    val col: Int,
+    val len: Int,
+)
+
+class IntToken(
+    col: Int,
+    len: Int,
+    val value: Int,
+) : Token(col, len)
+
+class FloatToken(
+    col: Int,
+    len: Int,
+    val value: Float,
+) : Token(col, len)
+
+class InvalidNumberToken(
+    col: Int,
+    len: Int,
+) : Token(col, len)
+
+class RegisterToken(
+    col: Int,
+    len: Int,
+    val value: Int,
+) : Token(col, len)
+
+class LabelToken(
+    col: Int,
+    len: Int,
+    val value: Int,
+) : Token(col, len)
+
+sealed class SectionToken(col: Int, len: Int) : Token(col, len)
+
+class CodeSectionToken(
+    col: Int,
+    len: Int,
+) : SectionToken(col, len)
+
+class DataSectionToken(
+    col: Int,
+    len: Int,
+) : SectionToken(col, len)
+
+class StringSectionToken(
+    col: Int,
+    len: Int,
+) : SectionToken(col, len)
+
+class InvalidSectionToken(
+    col: Int,
+    len: Int,
+) : Token(col, len)
+
+class StringToken(
+    col: Int,
+    len: Int,
+    val value: String,
+) : Token(col, len)
+
+class UnterminatedStringToken(
+    col: Int,
+    len: Int,
+    val value: String,
+) : Token(col, len)
+
+class IdentToken(
+    col: Int,
+    len: Int,
+    val value: String,
+) : Token(col, len)
+
+class InvalidIdentToken(
+    col: Int,
+    len: Int,
+) : Token(col, len)
+
+class ArgSeparatorToken(
+    col: Int,
+    len: Int,
+) : Token(col, len)
+
+fun tokenizeLine(line: String): MutableList<Token> =
+    LineTokenizer(line).tokenize()
+
+private class LineTokenizer(private var line: String) {
+    private var index = 0
+
+    private val col: Int
+        get() = index + 1
+
+    private var mark = 0
+
+    fun tokenize(): MutableList<Token> {
+        val tokens = mutableListOf<Token>()
+
+        while (hasNext()) {
+            val char = peek()
+            var token: Token
+
+            if (char == '/') {
+                skip()
+
+                if (peek() == '/') {
+                    // It's a comment.
+                    break
+                } else {
+                    back()
+                }
+            }
+
+            if (char.isWhitespace()) {
+                skip()
+                continue
+            } else if (char == '-' || char.isDigit()) {
+                token = tokenizeNumberOrLabel()
+            } else if (char == ',') {
+                token = ArgSeparatorToken(col, 1)
+                skip()
+            } else if (char == '.') {
+                token = tokenizeSection()
+            } else if (char == '"') {
+                token = tokenizeString()
+            } else if (char == 'r') {
+                token = tokenizeRegisterOrIdent()
+            } else {
+                token = tokenizeIdent()
+            }
+
+            tokens.add(token)
+        }
+
+        return tokens
+    }
+
+    private fun hasNext(): Boolean = index < line.length
+
+    private fun next(): Char = line[index++]
+
+    private fun peek(): Char = line[index]
+
+    private fun skip() {
+        index++
+    }
+
+    private fun back() {
+        index--
+    }
+
+    private fun mark() {
+        mark = index
+    }
+
+    private fun markedLen(): Int = index - mark
+
+    private fun slice(): String = line.substring(mark, index)
+
+    private fun eatRestOfToken() {
+        while (hasNext()) {
+            val char = next()
+
+            if (char == ',' || char.isWhitespace()) {
+                back()
+                break
+            }
+        }
+    }
+
+    private fun tokenizeNumberOrLabel(): Token {
+        mark()
+        val col = this.col
+        skip()
+        var isLabel = false
+
+        while (hasNext()) {
+            val char = peek()
+
+            if (char == '.' || char == 'e') {
+                return tokenizeFloat(col)
+            } else if (char == 'x') {
+                return tokenizeHexNumber(col)
+            } else if (char == ':') {
+                isLabel = true
+                skip()
+                break
+            } else if (char == ',' || char.isWhitespace()) {
+                break
+            } else {
+                skip()
+            }
+        }
+
+        val value = slice().toIntOrNull()
+            ?: return InvalidNumberToken(col, markedLen())
+
+        return if (isLabel) {
+            LabelToken(col, markedLen(), value)
+        } else {
+            IntToken(col, markedLen(), value)
+        }
+    }
+
+    private fun tokenizeHexNumber(col: Int): Token {
+        eatRestOfToken()
+        val hexStr = slice()
+
+        if (HEX_INT_REGEX.matches(hexStr)) {
+            hexStr.toIntOrNull(16)?.let { value ->
+                return IntToken(col, markedLen(), value)
+            }
+        }
+
+        return InvalidNumberToken(col, markedLen())
+    }
+
+    private fun tokenizeFloat(col: Int): Token {
+        eatRestOfToken()
+        val floatStr = slice()
+
+        if (FLOAT_REGEX.matches(floatStr)) {
+            floatStr.toFloatOrNull()?.let { value ->
+                return FloatToken(col, markedLen(), value)
+            }
+        }
+
+        return InvalidNumberToken(col, markedLen())
+    }
+
+    private fun tokenizeRegisterOrIdent(): Token {
+        val col = this.col
+        skip()
+        mark()
+        var isRegister = false
+
+        while (hasNext()) {
+            val char = peek()
+
+            if (char.isDigit()) {
+                isRegister = true
+                skip()
+            } else {
+                break
+            }
+        }
+
+        return if (isRegister) {
+            val value = slice().toInt()
+
+            RegisterToken(col, markedLen() + 1, value)
+        } else {
+            back()
+            tokenizeIdent()
+        }
+    }
+
+    private fun tokenizeSection(): Token {
+        val col = this.col
+        mark()
+
+        while (hasNext()) {
+            if (peek().isWhitespace()) {
+                break
+            } else {
+                skip()
+            }
+        }
+
+        return when (slice()) {
+            ".code" -> CodeSectionToken(col, 5)
+            ".data" -> DataSectionToken(col, 5)
+            ".string" -> StringSectionToken(col, 7)
+            else -> InvalidSectionToken(col, markedLen())
+        }
+    }
+
+    private fun tokenizeString(): Token {
+        val col = this.col
+        skip()
+        mark()
+        var prevWasBackSpace = false
+        var terminated = false
+
+        while (hasNext()) {
+            when (peek()) {
+                '\\' -> {
+                    prevWasBackSpace = true
+                }
+                '"' -> {
+                    if (!prevWasBackSpace) {
+                        terminated = true
+                        break
+                    }
+
+                    prevWasBackSpace = false
+                }
+                else -> {
+                    prevWasBackSpace = false
+                }
+            }
+
+            next()
+        }
+
+        val value = slice().replace("\\\"", "\"").replace("\\n", "\n")
+
+        return if (terminated) {
+            next()
+            StringToken(col, markedLen() + 2, value)
+        } else {
+            UnterminatedStringToken(col, markedLen() + 1, value)
+        }
+    }
+
+    private fun tokenizeIdent(): Token {
+        val col = this.col
+        mark()
+
+        while (hasNext()) {
+            val char = peek()
+
+            if (char == ',' || char.isWhitespace()) {
+                break
+            } else if (char == '/') {
+                skip()
+
+                if (peek() == '/') {
+                    back()
+                    break
+                }
+            } else {
+                skip()
+            }
+        }
+
+        val value = slice()
+
+        return if (IDENT_REGEX.matches(value)) {
+            IdentToken(col, markedLen(), value)
+        } else {
+            InvalidIdentToken(col, markedLen())
+        }
+    }
+}
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Instructions.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Instructions.kt
index d74be29b..1685bed9 100644
--- a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Instructions.kt
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Instructions.kt
@@ -103,25 +103,29 @@ enum class SegmentType {
  * referenced by one or more labels. The segment ends right before the next instruction, byte or
  * string character that is referenced by a label.
  */
-sealed class Segment(val type: SegmentType, val labels: MutableList<Int>)
+sealed class Segment(
+    val type: SegmentType,
+    val labels: MutableList<Int>,
+    val srcLoc: SegmentSrcLoc,
+)
 
 class InstructionSegment(
     labels: MutableList<Int>,
-    val instructions: List<Instruction>,
-    val srcLoc: SegmentSrcLoc,
-) : Segment(SegmentType.Instructions, labels)
+    val instructions: MutableList<Instruction>,
+    srcLoc: SegmentSrcLoc,
+) : Segment(SegmentType.Instructions, labels, srcLoc)
 
 class DataSegment(
     labels: MutableList<Int>,
     val data: Buffer,
-    val srcLoc: SegmentSrcLoc,
-) : Segment(SegmentType.Data, labels)
+    srcLoc: SegmentSrcLoc,
+) : Segment(SegmentType.Data, labels, srcLoc)
 
 class StringSegment(
     labels: MutableList<Int>,
-    val value: String,
-    val srcLoc: SegmentSrcLoc,
-) : Segment(SegmentType.String, labels)
+    var value: String,
+    srcLoc: SegmentSrcLoc,
+) : Segment(SegmentType.String, labels, srcLoc)
 
 /**
  * Position and length of related source assembly code.
@@ -144,9 +148,9 @@ class InstructionSrcLoc(
 /**
  * Locations of an instruction's stack arguments in the source assembly code.
  */
-class StackArgSrcLoc(lineNo: Int, col: Int, len: Int, val value: Int) : SrcLoc(lineNo, col, len)
+class StackArgSrcLoc(lineNo: Int, col: Int, len: Int, val value: Any) : SrcLoc(lineNo, col, len)
 
 /**
  * Locations of a segment's labels in the source assembly code.
  */
-class SegmentSrcLoc(val labels: List<SrcLoc>)
+class SegmentSrcLoc(val labels: MutableList<SrcLoc> = mutableListOf())
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Opcode.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Opcode.kt
index 815b6f3a..72da7b9f 100644
--- a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Opcode.kt
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/Opcode.kt
@@ -1,5 +1,16 @@
 package world.phantasmal.lib.assembly
 
+private val MNEMONIC_TO_OPCODES: MutableMap<String, Opcode> by lazy {
+    val map = mutableMapOf<String, Opcode>()
+
+    OPCODES.forEach { if (it != null) map[it.mnemonic] = it }
+    OPCODES_F8.forEach { if (it != null) map[it.mnemonic] = it }
+    OPCODES_F9.forEach { if (it != null) map[it.mnemonic] = it }
+
+    map
+}
+private val UNKNOWN_OPCODE_MNEMONIC_REGEX = Regex("""^unknown_((f8|f9)?[0-9a-f]{2})$""")
+
 /**
  * Abstract super type of all types.
  */
@@ -164,6 +175,20 @@ fun codeToOpcode(code: Int): Opcode =
         else -> getOpcode(code, code and 0xFF, OPCODES_F9)
     }
 
+fun mnemonicToOpcode(mnemonic: String): Opcode? {
+    var opcode = MNEMONIC_TO_OPCODES[mnemonic]
+
+    if (opcode == null) {
+        UNKNOWN_OPCODE_MNEMONIC_REGEX.matchEntire(mnemonic)?.destructured?.let { (codeStr) ->
+            val code = codeStr.toInt(16)
+            opcode = codeToOpcode(code)
+            MNEMONIC_TO_OPCODES[mnemonic] = opcode!!
+        }
+    }
+
+    return opcode
+}
+
 private fun getOpcode(code: Int, index: Int, opcodes: Array<Opcode?>): Opcode {
     var opcode = opcodes[index]
 
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/dataFlowAnalysis/ControlFlowGraph.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/dataFlowAnalysis/ControlFlowGraph.kt
index 4b496290..c4320069 100644
--- a/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/dataFlowAnalysis/ControlFlowGraph.kt
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/assembly/dataFlowAnalysis/ControlFlowGraph.kt
@@ -1,10 +1,309 @@
 package world.phantasmal.lib.assembly.dataFlowAnalysis
 
-import world.phantasmal.lib.assembly.InstructionSegment
+import world.phantasmal.lib.assembly.*
+
+// See https://en.wikipedia.org/wiki/Control-flow_graph.
+
+enum class BranchType {
+    None,
+    Return,
+    Jump,
+    ConditionalJump,
+    Call,
+}
+
+/**
+ * Instruction sequence into which control flow only enters at the start and only leaves at the end.
+ * No code jumps/returns/calls into the middle of a basic block or branches out of a basic block
+ * from the middle.
+ */
+interface BasicBlock {
+    /**
+     * The instruction segment that this block is a part of.
+     */
+    val segment: InstructionSegment
+
+    /**
+     * Index of this block's first instruction.
+     */
+    val start: Int
+
+    /**
+     * Index of the instruction right after this block's last instruction.
+     */
+    val end: Int
+
+    /**
+     * The way control flow leaves this block.
+     */
+    val branchType: BranchType
+
+    /**
+     * Either jumps or calls when non-empty, depending on [branchType].
+     */
+    val branchLabels: List<Int>
+
+    /**
+     * The blocks which branch to this block.
+     */
+    val from: List<BasicBlock>
+
+    /**
+     * The blocks this block branches to.
+     */
+    val to: List<BasicBlock>
+}
+
+/**
+ * Graph representing the flow of control through the [BasicBlock]s of a script.
+ */
+class ControlFlowGraph(
+    val blocks: List<BasicBlock>,
+    private val instructionsToBlock: Map<Instruction, BasicBlock>,
+) {
+    fun getBlockForInstruction(instruction: Instruction): BasicBlock? =
+        instructionsToBlock[instruction]
 
-class ControlFlowGraph {
     companion object {
-        fun create(segments: List<InstructionSegment>): ControlFlowGraph =
-            TODO()
+        fun create(segments: List<InstructionSegment>): ControlFlowGraph {
+            val cfg = ControlFlowGraphBuilder()
+
+            // Mapping of labels to basic blocks.
+            for (segment in segments) {
+                createBasicBlocks(cfg, segment)
+            }
+
+            linkBlocks(cfg)
+            return cfg.build()
+        }
+    }
+}
+
+private class ControlFlowGraphBuilder {
+    val blocks: MutableList<BasicBlockImpl> = mutableListOf()
+    val instructionsToBlock: MutableMap<Instruction, BasicBlockImpl> = mutableMapOf()
+    val labelsToBlock: MutableMap<Int, BasicBlockImpl> = mutableMapOf()
+
+    fun build(): ControlFlowGraph =
+        ControlFlowGraph(blocks, instructionsToBlock)
+}
+
+class BasicBlockImpl(
+    override val segment: InstructionSegment,
+    override val start: Int,
+    override val end: Int,
+    override val branchType: BranchType,
+    override val branchLabels: List<Int>,
+) : BasicBlock {
+    override val from: MutableList<BasicBlockImpl> = mutableListOf()
+    override val to: MutableList<BasicBlockImpl> = mutableListOf()
+
+    fun linkTo(other: BasicBlockImpl) {
+        if (other !in to) {
+            to.add(other)
+            other.from.add(this)
+        }
+    }
+
+    fun indexOfInstruction(instruction: Instruction): Int {
+        var index = -1
+
+        for (i in start until end) {
+            if (instruction == segment.instructions[i]) {
+                index = i
+                break
+            }
+        }
+
+        return index
+    }
+}
+
+private fun createBasicBlocks(cfg: ControlFlowGraphBuilder, segment: InstructionSegment) {
+    val len = segment.instructions.size
+    var start = 0
+    var firstBlock = true
+
+    for (i in 0 until len) {
+        val inst = segment.instructions[i]
+
+        var branchType: BranchType
+        var branchLabels: List<Int>
+
+        when (inst.opcode) {
+            // Return.
+            OP_RET -> {
+                branchType = BranchType.Return
+                branchLabels = emptyList()
+            }
+
+            // Unconditional jump.
+            OP_JMP -> {
+                branchType = BranchType.Jump
+                branchLabels = listOf(inst.args[0].value as Int)
+            }
+
+            // Conditional jumps.
+            OP_JMP_ON,
+            OP_JMP_OFF,
+            -> {
+                branchType = BranchType.ConditionalJump
+                branchLabels = listOf(inst.args[0].value as Int)
+            }
+            OP_JMP_E,
+            OP_JMPI_E,
+            OP_JMP_NE,
+            OP_JMPI_NE,
+            OP_UJMP_G,
+            OP_UJMPI_G,
+            OP_JMP_G,
+            OP_JMPI_G,
+            OP_UJMP_L,
+            OP_UJMPI_L,
+            OP_JMP_L,
+            OP_JMPI_L,
+            OP_UJMP_GE,
+            OP_UJMPI_GE,
+            OP_JMP_GE,
+            OP_JMPI_GE,
+            OP_UJMP_LE,
+            OP_UJMPI_LE,
+            OP_JMP_LE,
+            OP_JMPI_LE,
+            -> {
+                branchType = BranchType.ConditionalJump
+                branchLabels = listOf(inst.args[2].value as Int)
+            }
+            OP_SWITCH_JMP -> {
+                branchType = BranchType.ConditionalJump
+                branchLabels = inst.args.drop(1).map { it.value as Int }
+            }
+
+            // Calls.
+            OP_CALL,
+            OP_VA_CALL,
+            -> {
+                branchType = BranchType.Call
+                branchLabels = listOf(inst.args[0].value as Int)
+            }
+            OP_SWITCH_CALL -> {
+                branchType = BranchType.Call
+                branchLabels = inst.args.drop(1).map { it.value as Int }
+            }
+
+            // All other opcodes.
+            else -> {
+                if (i == len - 1) {
+                    // This is the last block of the segment.
+                    branchType = BranchType.None
+                    branchLabels = emptyList()
+                } else {
+                    // Non-branching instruction, part of the current block.
+                    continue
+                }
+            }
+        }
+
+        val block = BasicBlockImpl(segment, start, i + 1, branchType, branchLabels)
+
+        for (j in block.start until block.end) {
+            cfg.instructionsToBlock[block.segment.instructions[j]] = block
+        }
+
+        cfg.blocks.add(block)
+
+        if (firstBlock) {
+            for (label in segment.labels) {
+                cfg.labelsToBlock[label] = block
+            }
+
+            firstBlock = false
+        }
+
+        start = i + 1
+    }
+}
+
+private fun linkBlocks(cfg: ControlFlowGraphBuilder) {
+    // Pairs of calling block and block to which callees should return to.
+    val callers = mutableListOf<Pair<BasicBlockImpl, BasicBlockImpl>>()
+
+    for (i in cfg.blocks.indices) {
+        val block = cfg.blocks[i]
+        val nextBlock = cfg.blocks.getOrNull(i + 1)
+
+        when (block.branchType) {
+            BranchType.Return ->
+                continue
+
+            BranchType.Call ->
+                nextBlock?.let { callers.add(block to nextBlock); }
+
+            BranchType.None,
+            BranchType.ConditionalJump,
+            -> nextBlock?.let(block::linkTo)
+
+            else -> {
+                // Ignore.
+            }
+        }
+
+        for (label in block.branchLabels) {
+            cfg.labelsToBlock[label]?.let { toBlock ->
+                block.linkTo(toBlock)
+            }
+        }
+    }
+
+    for ((caller, ret) in callers) {
+        linkReturningBlocks(cfg.labelsToBlock, ret, caller)
+    }
+}
+
+/**
+ * Links returning blocks to their callers.
+ *
+ * @param labelBlocks Mapping of labels to basic blocks.
+ * @param ret Basic block the caller should return to.
+ * @param caller Calling basic block.
+ */
+private fun linkReturningBlocks(
+    labelBlocks: Map<Int, BasicBlockImpl>,
+    ret: BasicBlockImpl,
+    caller: BasicBlockImpl,
+) {
+    for (label in caller.branchLabels) {
+        labelBlocks[label]?.let { callee ->
+            if (callee.branchType === BranchType.Return) {
+                callee.linkTo(ret)
+            } else {
+                linkReturningBlocksRecurse(mutableSetOf(), ret, callee)
+            }
+        }
+    }
+}
+
+/**
+ * @param encountered For avoiding infinite loops.
+ * @param ret
+ * @param block
+ */
+private fun linkReturningBlocksRecurse(
+    encountered: MutableSet<BasicBlockImpl>,
+    ret: BasicBlockImpl,
+    block: BasicBlockImpl,
+) {
+    if (block in encountered) {
+        return
+    } else {
+        encountered.add(block)
+    }
+
+    for (toBlock in block.to) {
+        if (toBlock.branchType === BranchType.Return) {
+            toBlock.linkTo(ret)
+        } else {
+            linkReturningBlocksRecurse(encountered, ret, toBlock)
+        }
     }
 }
diff --git a/lib/src/commonMain/kotlin/world/phantasmal/lib/fileFormats/quest/ObjectCode.kt b/lib/src/commonMain/kotlin/world/phantasmal/lib/fileFormats/quest/ObjectCode.kt
index f0650f3e..219713b4 100644
--- a/lib/src/commonMain/kotlin/world/phantasmal/lib/fileFormats/quest/ObjectCode.kt
+++ b/lib/src/commonMain/kotlin/world/phantasmal/lib/fileFormats/quest/ObjectCode.kt
@@ -368,7 +368,7 @@ private fun parseInstructionsSegment(
     val segment = InstructionSegment(
         labels,
         instructions,
-        SegmentSrcLoc(emptyList())
+        SegmentSrcLoc()
     )
     offsetToSegment[cursor.position.toInt()] = segment
 
@@ -437,7 +437,7 @@ private fun parseDataSegment(
     val segment = DataSegment(
         labels,
         cursor.buffer(endOffset.toUInt() - startOffset),
-        SegmentSrcLoc(listOf()),
+        SegmentSrcLoc(),
     )
     offsetToSegment[startOffset.toInt()] = segment
 }
@@ -465,7 +465,7 @@ private fun parseStringSegment(
                 dropRemaining = true
             )
         },
-        SegmentSrcLoc(listOf())
+        SegmentSrcLoc()
     )
     offsetToSegment[startOffset.toInt()] = segment
 }