Merge pull request #1551 from hylo-lang/collection-algorithms

Implement some algorithms on `Collection`

StandardLibrary/Sources/Core/Collection.hylo

@@ -28,6 +28,28 @@ public trait Collection {
 
 public extension Collection {
 
+  /// Returns the number of elements in `self`.
+  ///
+  /// - Complexity: O(n), where n is the number of elements in `self`.
+  public fun count() -> Int {
+    var r = 0
+    for let _ in self { &r += 1 }
+    return r
+  }
+
+  /// Returns the position of the first element of `self` satisfying `predicate`, or
+  /// `end_position()` if no such element exists.
+  ///
+  /// - Complexity: O(n), where n is the number of elements in `self`.
+  public fun first_position<E>(where predicate: [E](Element) -> Bool) -> Position {
+    var i = start_position()
+    let j = end_position()
+    while (i != j) && !predicate(self[i]) {
+      &i = self.position(after: i)
+    }
+    return i
+  }
+
   /// Returns the result of applying `combine` on an accumulator, initialized with `initial_value`,
   /// and each element of `self`, in order.
   ///
@@ -63,3 +85,15 @@ public extension Collection {
   }
 
 }
+
+public extension Collection where Element: Equatable {
+
+  /// Returns the position of the first element of `self` that is equal to `needle`, or
+  /// `end_position()` if no such element exists.
+  ///
+  /// - Complexity: O(n), where n is the number of elements in `self`.
+  public fun first_position(of needle: Element) -> Position {
+    first_position(where: fun (_ e) { e == needle })
+  }
+
+}

Tests/LibraryTests/TestCases/CollectionTests.hylo

@@ -1,5 +1,29 @@
 //- compileAndRun expecting: .success
 
+conformance Int: Collection {
+
+  public typealias Element = Bool
+  public typealias Position = Int
+
+  public fun start_position() -> Int { 0 }
+  public fun end_position() -> Int { Int.bit_width() }
+  public fun position(after p: Int) -> Int { p + 1 }
+
+  public subscript(_ p: Int): Bool { (self & (1 << p)) != 0 }
+
+}
+
+fun test_count() {
+  let a = 0
+  precondition(a.count() == 64)
+}
+
+fun test_first_position() {
+  let a = 4
+  precondition(a.first_position(where: fun (_ x) { x.copy() }) == 2)
+  precondition(a.first_position(of: true) == 2)
+}
+
 fun test_reduce() {
   var a = Array<Int>()
   &a.append(1)
@@ -31,6 +55,8 @@ fun test_all_satisfy() {
 }
 
 public fun main() {
+  test_count()
+  test_first_position()
   test_reduce()
   test_contains_where()
   test_all_satisfy()