Added docs and clarifications to functional typealiases

Author: Jolanrensen

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/aliases.kt

@@ -8,32 +8,130 @@ import org.jetbrains.kotlinx.dataframe.columns.ColumnSet
 import org.jetbrains.kotlinx.dataframe.columns.ColumnWithPath
 import org.jetbrains.kotlinx.dataframe.columns.SingleColumn
 
-public typealias Predicate<T> = (T) -> Boolean
-
-public typealias Selector<T, R> = T.(T) -> R
+/**
+ * [Predicate] is used to reach a [Boolean] result using the given instance of `T` as `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * (it: T) -> Boolean
+ * ```
+ */
+public typealias Predicate<T> = (it: T) -> Boolean
+
+/**
+ * [Selector] is used to express or select any instance of `R` using the given instance of `T` as `this` and `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * T.(it: T) -> R
+ * ```
+ */
+public typealias Selector<T, R> = T.(it: T) -> R
 
 // region selectors
 
+/**
+ * [DataFrameExpression] is used to express or select any instance of `R` using the given instance of [DataFrame]`<T>`
+ * as `this` and `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * DataFrame<T>.(it: DataFrame<T>) -> R
+ * ```
+ */
 public typealias DataFrameExpression<T, R> = Selector<DataFrame<T>, R>
 
+/**
+ * [RowExpression] is used to express or select any instance of `R` using the given instance of [DataRow]`<T>` as
+ * `this` and `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * DataRow<T>.(it: DataRow<T>) -> R
+ * ```
+ */
 public typealias RowExpression<T, R> = Selector<DataRow<T>, R>
 
-public typealias RowValueExpression<T, C, R> = DataRow<T>.(C) -> R
-
-public typealias RowColumnExpression<T, C, R> = (DataRow<T>, DataColumn<C>) -> R
-
+/**
+ * [RowValueExpression] is used to express or select any instance of `R` using the given value `it: C` and the given
+ * instance of [DataRow]`<T>` as `this`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * DataRow<T>.(it: C) -> R
+ * ```
+ */
+public typealias RowValueExpression<T, C, R> = DataRow<T>.(it: C) -> R
+
+/**
+ * [RowColumnExpression] is used to express or select any instance of `R` using the given instances of
+ * [DataRow]`<T>` as `row` and [DataColumn]`<C>` as `col`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * (row: DataRow<T>, col: DataColumn<C>) -> R
+ * ```
+ */
+public typealias RowColumnExpression<T, C, R> = (row: DataRow<T>, col: DataColumn<C>) -> R
+
+/**
+ * [ColumnSelector] is used to express or select a single column, represented by [SingleColumn]`<C>`, using the
+ * context of [ColumnsSelectionDsl]`<T>` as `this` and `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * ColumnsSelectionDsl<T>.(it: ColumnsSelectionDsl<T>) -> SingleColumn<C>
+ * ```
+ */
 public typealias ColumnSelector<T, C> = Selector<ColumnsSelectionDsl<T>, SingleColumn<C>>
 
+/**
+ * [ColumnsSelector] is used to express or select multiple columns, represented by [ColumnSet]`<C>`, using the
+ * context of [ColumnsSelectionDsl]`<T>` as `this` and `it`.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * ColumnsSelectionDsl<T>.(it: ColumnsSelectionDsl<T>) -> ColumnSet<C>
+ * ```
+ */
 public typealias ColumnsSelector<T, C> = Selector<ColumnsSelectionDsl<T>, ColumnSet<C>>
 
 // endregion
 
 // region filters
 
+/**
+ * [RowFilter] is used to filter or find rows using the given instance of [DataRow]`<T>` as `this` and `it`.
+ * Return `true` if the row should be included in the result.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * DataRow<T>.(it: DataRow<T>) -> Boolean
+ * ```
+ */
 public typealias RowFilter<T> = RowExpression<T, Boolean>
 
-public typealias ColumnFilter<T> = (ColumnWithPath<T>) -> Boolean
-
+/**
+ * [ColumnFilter] is used to filter or find columns using the given instance of [ColumnWithPath]`<T>` as `it`.
+ * Return `true` if the column should be included in the result.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * (it: ColumnWithPath<T>) -> Boolean
+ * ```
+ */
+public typealias ColumnFilter<T> = Predicate<ColumnWithPath<T>>
+
+/**
+ * [RowValueFilter] is used to filter or find rows using the given value of `it: C` and the given instance of
+ * [DataRow]`<T>` as `this`.
+ * Return `true` if the row should be included in the result.
+ *
+ * Shorthand for:
+ * ```kotlin
+ * DataRow<T>.(it: C) -> Boolean
+ * ```
+ */
 public typealias RowValueFilter<T, C> = RowValueExpression<T, C, Boolean>
 
 // endregion