Implements #442 (#552)

* Implements #442.

* Address reviewer feedback.

Author: msoeken

Standard/src/Canon/Combinators/SinglyControlled.qs

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+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Quantum.Canon {
+
+    /// # Summary
+    /// Given a controllable operation, returns a controlled version of that operation
+    /// accepting exactly one control qubit.
+    ///
+    /// # Input
+    /// ## op
+    /// The operation to be controlled.
+    ///
+    /// # Output
+    /// A controlled variant of `op` accepting exactly one control qubit.
+    ///
+    /// # Example
+    /// To add the weight (number of "1" bits) of a control register to
+    /// a target register:
+    /// ```qsharp
+    /// ApplyToEachCA(
+    ///     SinglyControlled(IncrementByInteger)(_, (1, target)),
+    ///     controls)
+    /// );
+    /// ```
+    ///
+    /// # See Also
+    /// - Microsoft.Quantum.Canon.SinglyControlledA
+    function SinglyControlled<'T>(op : 'T => Unit is Ctl) : (Qubit, 'T) => Unit is Ctl {
+        return (ctrl, originalInput) => Controlled op([ctrl], originalInput);
+    }
+
+    /// # Summary
+    /// Given a controllable operation, returns a controlled version of that operation
+    /// accepting exactly one control qubit.
+    ///
+    /// # Input
+    /// ## op
+    /// The operation to be controlled.
+    ///
+    /// # Output
+    /// A controlled variant of `op` accepting exactly one control qubit.
+    ///
+    /// # Example
+    /// To add the weight (number of "1" bits) of a control register to
+    /// a target register:
+    /// ```qsharp
+    /// ApplyToEachCA(
+    ///     SinglyControlledA(IncrementByInteger)(_, (1, target)),
+    ///     controls)
+    /// );
+    /// ```
+    ///
+    /// # See Also
+    /// - Microsoft.Quantum.Canon.SinglyControlled
+    function SinglyControlledA<'T>(op : 'T => Unit is Adj + Ctl) : (Qubit, 'T) => Unit is Adj + Ctl {
+        return (ctrl, originalInput) => Controlled op([ctrl], originalInput);
+    }
+
+}

Standard/tests/Canon/Combinators/SinglyControlled.qs

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+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Microsoft.Quantum.Tests {
+    open Microsoft.Quantum.Arithmetic;
+    open Microsoft.Quantum.Canon;
+    open Microsoft.Quantum.Diagnostics;
+    open Microsoft.Quantum.Intrinsic;
+
+    @Test("ToffoliSimulator")
+    operation TestSinglyControlledWithSimulation() : Unit {
+        use ctl = Qubit();
+        use target = Qubit[3];
+        let targetLE = LittleEndian(target);
+        let value = 5;
+
+        for singlyControlled in [SinglyControlled, SinglyControlledA] {
+            for enableControl in [false, true] {
+                within {
+                    ApplyIfA(enableControl, X, ctl);
+                } apply {
+                    singlyControlled(ApplyXorInPlace(value, _))(ctl, targetLE);
+                    EqualityFactI(MeasureInteger(targetLE), enableControl ? value | 0, "Unexpected measurement result for SinglyControlled");
+                }
+            }
+        }
+    }
+
+    @Test("QuantumSimulator")
+    operation TestSinglyControlledWithEquivalenceCheck() : Unit {
+        AssertOperationsEqualReferenced(2,
+            qs => SinglyControlled(H)(qs[0], qs[1]),
+            qs => Controlled H([qs[0]], qs[1])
+        );
+    }
+}