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Improvements to tuples: Rearrange types into a more logical order
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‎library/src/scala/Tuple.scala

+64-67
Original file line numberDiff line numberDiff line change
@@ -101,75 +101,95 @@ sealed trait Tuple extends Product:
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object Tuple:
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/** Type of a tuple with an element appended */
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type Append[X <: Tuple, Y] <: NonEmptyTuple = X match {
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case EmptyTuple => Y *: EmptyTuple
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case x *: xs => x *: Append[xs, Y]
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}
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/** The size of a tuple, represented as a literal constant subtype of Int */
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type Size[X <: Tuple] <: Int = X match
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case EmptyTuple => 0
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case x *: xs => S[Size[xs]]
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/** The type of the element at position N in the tuple X */
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type Elem[X <: Tuple, N <: Int] = X match
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case x *: xs =>
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N match
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case 0 => x
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case S[n1] => Elem[xs, n1]
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/** Type of the head of a tuple */
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type Head[X <: Tuple] = X match {
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/** The type of the first element of a tuple */
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type Head[X <: Tuple] = X match
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case x *: _ => x
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}
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/** Type of the initial part of the tuple without its last element */
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type Init[X <: Tuple] <: Tuple = X match {
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/** The type of the last element of a tuple */
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type Last[X <: Tuple] = X match
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case x *: EmptyTuple => x
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case _ *: xs => Last[xs]
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/** The type of a tuple consisting of all elements of tuple X except the first one */
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type Tail[X <: Tuple] <: Tuple = X match
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case _ *: xs => xs
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/** The type of the initial part of a tuple without its last element */
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type Init[X <: Tuple] <: Tuple = X match
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case _ *: EmptyTuple => EmptyTuple
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case x *: xs =>
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x *: Init[xs]
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}
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122-
/** Type of the tail of a tuple */
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type Tail[X <: Tuple] <: Tuple = X match {
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case _ *: xs => xs
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}
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/** The type of the tuple consisting of the first `N` elements of `X`,
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* or all elements if `N` exceeds `Size[X]`.
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*/
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type Take[X <: Tuple, N <: Int] <: Tuple = N match
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case 0 => EmptyTuple
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case S[n1] => X match
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case EmptyTuple => EmptyTuple
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case x *: xs => x *: Take[xs, n1]
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127-
/** Type of the last element of a tuple */
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type Last[X <: Tuple] = X match {
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case x *: EmptyTuple => x
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case _ *: xs => Last[xs]
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/** The type of the tuple consisting of all elements of `X` except the first `N` ones,
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* or no elements if `N` exceeds `Size[X]`.
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*/
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type Drop[X <: Tuple, N <: Int] <: Tuple = N match {
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case 0 => X
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case S[n1] => X match {
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case EmptyTuple => EmptyTuple
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case x *: xs => Drop[xs, n1]
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}
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}
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133-
/** Type of the concatenation of two tuples */
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type Concat[X <: Tuple, +Y <: Tuple] <: Tuple = X match {
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case EmptyTuple => Y
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case x1 *: xs1 => x1 *: Concat[xs1, Y]
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}
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/** The pair type `(Take(X, N), Drop[X, N]). */
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type Split[X <: Tuple, N <: Int] = (Take[X, N], Drop[X, N])
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139-
/** Type of the element at position N in the tuple X */
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type Elem[X <: Tuple, N <: Int] = X match {
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case x *: xs =>
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N match {
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case 0 => x
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case S[n1] => Elem[xs, n1]
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}
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/** Type of a tuple with an element appended */
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type Append[X <: Tuple, Y] <: NonEmptyTuple = X match {
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case EmptyTuple => Y *: EmptyTuple
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case x *: xs => x *: Append[xs, Y]
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}
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148-
/** Literal constant Int size of a tuple */
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type Size[X <: Tuple] <: Int = X match {
150-
case EmptyTuple => 0
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case x *: xs => S[Size[xs]]
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}
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/** Type of the concatenation of two tuples `X` and `Y` */
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type Concat[X <: Tuple, +Y <: Tuple] <: Tuple = X match
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case EmptyTuple => Y
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case x1 *: xs1 => x1 *: Concat[xs1, Y]
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/** Fold a tuple `(T1, ..., Tn)` into `F[T1, F[... F[Tn, Z]...]]]` */
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type Fold[Tup <: Tuple, Z, F[_, _]] = Tup match
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case EmptyTuple => Z
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case h *: t => F[h, Fold[t, Z, F]]
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159-
/** Converts a tuple `(T1, ..., Tn)` to `(F[T1], ..., F[Tn])` */
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type Map[Tup <: Tuple, F[_ <: Union[Tup]]] <: Tuple = Tup match {
174+
/** The type of tuple `X` mapped with the type-level function `F`.
175+
* If `X = (T1, ..., Ti)` then `Map[X, F] = `(F[T1], ..., F[Ti])`.
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*/
177+
type Map[Tup <: Tuple, F[_ <: Union[Tup]]] <: Tuple = Tup match
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case EmptyTuple => EmptyTuple
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case h *: t => F[h] *: Map[t, F]
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}
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165-
/** Converts a tuple `(T1, ..., Tn)` to a flattened `(..F[T1], ..., ..F[Tn])` */
166-
type FlatMap[Tup <: Tuple, F[_ <: Union[Tup]] <: Tuple] <: Tuple = Tup match {
181+
/** The type of tuple `X` flat-mapped with the type-level function `F`.
182+
* If `X = (T1, ..., Ti)` then `FlatMap[X, F] = `F[T1] ++ ... ++ F[Ti]`
183+
*/
184+
type FlatMap[Tup <: Tuple, F[_ <: Union[Tup]] <: Tuple] <: Tuple = Tup match
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case EmptyTuple => EmptyTuple
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case h *: t => Concat[F[h], FlatMap[t, F]]
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}
187+
// TODO: implement term level analogue
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171-
/** Filters out those members of the tuple for which the predicate `P` returns `false`.
172-
* A predicate `P[X]` is a type that can be either `true` or `false`. For example:
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/** The type of the tuple consisting of all elements of tuple `X` that have types
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* for which the given type level predicate `P` reduces to the literal
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* constant `true`. A predicate `P[X]` is a type that can be either `true`
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* or `false`. For example:
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* ```scala
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* type IsString[x] <: Boolean = x match {
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* case String => true
@@ -233,29 +253,6 @@ object Tuple:
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case x *: xs => ReverseOnto[xs, x *: Acc]
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case EmptyTuple => Acc
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236-
/** Transforms a tuple `(T1, ..., Tn)` into `(T1, ..., Ti)`. */
237-
type Take[T <: Tuple, N <: Int] <: Tuple = N match {
238-
case 0 => EmptyTuple
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case S[n1] => T match {
240-
case EmptyTuple => EmptyTuple
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case x *: xs => x *: Take[xs, n1]
242-
}
243-
}
244-
245-
/** Transforms a tuple `(T1, ..., Tn)` into `(Ti+1, ..., Tn)`. */
246-
type Drop[T <: Tuple, N <: Int] <: Tuple = N match {
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case 0 => T
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case S[n1] => T match {
249-
case EmptyTuple => EmptyTuple
250-
case x *: xs => Drop[xs, n1]
251-
}
252-
}
253-
254-
/** Splits a tuple (T1, ..., Tn) into a pair of two tuples `(T1, ..., Ti)` and
255-
* `(Ti+1, ..., Tn)`.
256-
*/
257-
type Split[T <: Tuple, N <: Int] = (Take[T, N], Drop[T, N])
258-
259256
/** Given a tuple `(T1, ..., Tn)`, returns a union of its
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* member types: `T1 | ... | Tn`. Returns `Nothing` if the tuple is empty.
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*/

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