feat: add core storage value model and exception types

src/main/kotlin/kestrel/KestrelException.kt

@@ -0,0 +1,16 @@
+package kestrel
+
+open class KestrelException(message: String) : RuntimeException(message)
+
+class LexException(
+    message: String,
+    val line: Int,
+    val column: Int,
+    val incomplete: Boolean = false
+) : KestrelException("$message at line $line, column $column")
+
+class ParseException(
+    message: String,
+    val line: Int,
+    val column: Int
+) : KestrelException("$message at line $line, column $column")

src/main/kotlin/kestrel/storage/Row.kt

@@ -0,0 +1,3 @@
+package kestrel.storage
+
+data class Row(val values: List<Value>)

src/main/kotlin/kestrel/storage/Table.kt

@@ -0,0 +1,7 @@
+package kestrel.storage
+
+import kestrel.catalog.TableSchema
+
+class Table(val schema: TableSchema) {
+    val rows: MutableList<Row> = mutableListOf()
+}

src/main/kotlin/kestrel/storage/Value.kt

@@ -0,0 +1,52 @@
+package kestrel.storage
+
+enum class ColumnType {
+    Integer, Text, Boolean, Real;
+
+    val displayName: String
+        get() = when (this) {
+            Integer -> "INTEGER"
+            Text -> "TEXT"
+            Boolean -> "BOOLEAN"
+            Real -> "REAL"
+        }
+
+    companion object {
+        fun fromKeyword(keyword: String): ColumnType? = when (keyword.uppercase()) {
+            "INTEGER" -> Integer
+            "TEXT" -> Text
+            "BOOLEAN" -> Boolean
+            "REAL" -> Real
+            else -> null
+        }
+    }
+}
+
+sealed class Value {
+    abstract val type: ColumnType?
+
+    data class IntegerValue(val value: Long) : Value() {
+        override val type get() = ColumnType.Integer
+    }
+
+    data class RealValue(val value: Double) : Value() {
+        override val type get() = ColumnType.Real
+    }
+
+    data class TextValue(val value: String) : Value() {
+        override val type get() = ColumnType.Text
+    }
+
+    data class BooleanValue(val value: Boolean) : Value() {
+        override val type get() = ColumnType.Boolean
+    }
+
+    object NullValue : Value() {
+        override val type: ColumnType? get() = null
+    }
+
+    val isNull: Boolean get() = this is NullValue
+}
+
+val Value.typeName: String
+    get() = type?.displayName ?: "NULL"

src/main/kotlin/kestrel/storage/ValueOrdering.kt

@@ -0,0 +1,30 @@
+package kestrel.storage
+
+object ValueOrdering : Comparator<Value> {
+    override fun compare(left: Value, right: Value): Int = when {
+        left is Value.NullValue && right is Value.NullValue -> 0
+        left is Value.NullValue -> -1
+        right is Value.NullValue -> 1
+        left is Value.IntegerValue && right is Value.IntegerValue -> left.value.compareTo(right.value)
+        isNumeric(left) && isNumeric(right) -> asDouble(left).compareTo(asDouble(right))
+        left is Value.TextValue && right is Value.TextValue -> left.value.compareTo(right.value)
+        left is Value.BooleanValue && right is Value.BooleanValue -> left.value.compareTo(right.value)
+        else -> rank(left).compareTo(rank(right))
+    }
+
+    private fun isNumeric(value: Value): Boolean = value is Value.IntegerValue || value is Value.RealValue
+
+    private fun asDouble(value: Value): Double = when (value) {
+        is Value.IntegerValue -> value.value.toDouble()
+        is Value.RealValue -> value.value
+        else -> 0.0
+    }
+
+    private fun rank(value: Value): Int = when (value) {
+        is Value.NullValue -> 0
+        is Value.BooleanValue -> 1
+        is Value.IntegerValue -> 2
+        is Value.RealValue -> 2
+        is Value.TextValue -> 3
+    }
+}