Rename split-loop-with-lambda to slice-with-lambda

The refactoring is now published as Slice on sammancoaching.org:
https://sammancoaching.org/refactorings/slice.html

- git mv ideas/split-loop-with-lambda -> ideas/slice-with-lambda
- rename learning-hour file and update frontmatter name
- update paths in tools/rehearse scripts and report title
- update prose: 'Split Loop with Lambda' -> 'Slice with Lambda'
  in learning hour, exercise READMEs, storyboard, solution comments
- link the published Slice refactoring from the pattern draft

ideas/slice-with-lambda/exercise/csharp/IceCreamShop.cs

@@ -0,0 +1,79 @@
+// Example 3 — Ice cream shop demo of Slice with Lambda (C#)
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+//
+// Third repetition, same complexity as ScheduleWatering in WeatherStation.cs
+// (guard -> one dependency call -> map to enum -> constant tail), so
+// participants can practice extracting a lambda a second time. The C#
+// delegate syntax is worth the repetition:
+//
+//     Func<byte> readTemperature = () => _thermometer.Read();
+//
+// Cast:
+//   Thermometer     — hardware-ish dependency. Read() returns a raw
+//                     byte value (not calibrated, the client decides
+//                     what it means).
+//   Warmth          — enum. Reading > 25 => Warm, otherwise Cold.
+//                     (Sunny/Shady's cousin from WeatherStation.cs.)
+//   ThawAmount      — enum. None / Medium / Low.
+//   IceCreamShop    — the client. Owns the _thawedToday flag, so the
+//                     guard is about client state, not sensor state.
+
+using System;
+
+public enum Warmth
+{
+    Cold,
+    Warm
+}
+
+public enum ThawAmount
+{
+    None,
+    Medium,
+    Low
+}
+
+public class Thermometer
+{
+    private readonly Random _rng = new Random();    // stand-in for the hardware
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(50);                 // raw sensor value
+    }
+}
+
+public class IceCreamShop
+{
+    private readonly Thermometer _thermometer;
+    private bool _thawedToday;                      // event-style client state
+
+    public IceCreamShop(Thermometer thermometer)
+    {
+        _thermometer = thermometer;
+    }
+
+    public ThawAmount ThawStock()
+    {
+        if (_thawedToday)                           // guard: client state, stays
+        {
+            return ThawAmount.None;
+        }
+
+        _thawedToday = true;                        // set only after thawing
+        byte temperature = _thermometer.Read();     // middle: unwanted dependency
+        Warmth warmth = ToWarmth(temperature);
+        if (warmth == Warmth.Warm)                  // tail: complex behaviour below
+        {                                           // the extraction point
+            return ThawAmount.Medium;
+        }
+        return ThawAmount.Low;
+    }
+
+    private static Warmth ToWarmth(byte temperature)
+    {
+        return temperature > 25 ? Warmth.Warm : Warmth.Cold;
+    }
+}

ideas/slice-with-lambda/exercise/csharp/MetaphorFree.cs

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+// Example 1 — Metaphor-free demo of Slice with Lambda (C#)
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+//
+// Shape of the method (per zeroth-draft-of-refactoring-pattern.md):
+//
+//     guard clauses          — must run first
+//     middle: dependency     — one call on an object we don't want in the
+//                              extracted method
+//     tail: depends on b     — uses the value the dependency produced
+//
+// Deliberately NOT a loop: this is the smallest method that shows the
+// mechanics. The dependency both validates its precondition (using the
+// parameter a) and produces b — one expression, one thing to move into
+// the lambda.
+//
+// Unwanted dependency: SomeDependency — might throw when its precondition
+// on a is not satisfied, and returns an unpredictable value. An approval
+// test on Calculate is flaky until the lambda is stubbed.
+
+using System;
+
+public class Calculator
+{
+    private readonly SomeDependency _someDependency;
+
+    public Calculator(SomeDependency someDependency)
+    {
+        _someDependency = someDependency;
+    }
+
+    public int Calculate(int a)
+    {
+        if (a < 0) return 0;                    // guard clause: stays
+        int b = _someDependency.mightThrowWhenPreconditionNotSatisfied(a);  // middle: unwanted dependency
+        int c = a + b;                          // tail: depends on b
+        return c * 2;
+    }
+}
+
+public class SomeDependency
+{
+    private readonly Random _rng = new Random();    // stand-in for unpredictable computation
+
+    public int mightThrowWhenPreconditionNotSatisfied(int a)
+    {
+        if (a > 99)
+        {
+            throw new InvalidOperationException("precondition not satisfied");
+        }
+        return _rng.Next(100);
+    }
+}

ideas/slice-with-lambda/exercise/csharp/README.md

@@ -0,0 +1,44 @@
+# Slice with Lambda — C# demo examples
+
+Three C# demo examples for the **Slice with Lambda** refactoring.
+Condensed mechanics: https://www.sammancoaching.org/refactorings/slice.html
+(where that page says mock, we use a lambda instead).
+Full Java walkthrough: `../../storyboard/storyboard.md`.
+Slides: `~/qwan/slides-rjs/decks/refactoring/slice-with-lambda/slides.md`, served at http://localhost:9001/#/refactoring/slice-with-lambda.
+
+## The three examples
+
+| file | guard (client state) | unwanted dependency | lambda | tail |
+|---|---|---|---|---|
+| `MetaphorFree.cs` | `if (a < 0) return 0;` | `_someDependency.mightThrowWhenPreconditionNotSatisfied(a)` | `Func<int, int> readB = a => ...` | `int c = a + b; return c * 2;` |
+| `WeatherStation.cs` | `if (_wateredToday)` | `_lightSensor.Read()` (byte) | `Func<byte> readLight = () => ...` | sunny -> `WateringDuration.Medium`, shady -> `Short` (reading > 128 => `SunExposure.Sunny`) |
+| `IceCreamShop.cs` | `if (_thawedToday)` | `_thermometer.Read()` (byte) | `Func<byte> readTemperature = () => ...` | warm -> `ThawAmount.Medium`, cold -> `Low` (temperature > 25 => `Warmth.Warm`) |
+
+In all three, the guard reads client state (a parameter or a flag the client
+owns), so it stays in the extracted method. Only the dependency call moves
+into the lambda.
+
+## The ramp
+
+`MetaphorFree.cs` is the smallest possible shape: no loop, one dependency
+call, a tail of one arithmetic step. It carries the capture-to-parameter
+lesson: the lambda takes `a` as its parameter (`readB(a)`) because a lambda
+moved up into the function head cannot capture method parameters. Its
+step-4 stub tests include a throwing stub.
+
+`WeatherStation.cs` and `IceCreamShop.cs` are same-shape domain
+repetitions — guard, one dependency call, map to enum, constant tail — so
+participants can practice extracting the lambda twice. The C# delegate
+syntax (`Func<byte>`) is worth the repetition.
+
+## Same three regions every time
+
+Each example deliberately has the same three regions:
+
+- **before**: guard clauses
+- **middle**: one dependency call
+- **after**: tail that depends on the value the dependency produced
+
+Matching the pattern: extract the dependency-using code into a lambda,
+slide the definition to the top, extract the method below it, pass the
+lambda as parameter, test with pure lambda stubs.

ideas/slice-with-lambda/exercise/csharp/WeatherStation.cs

@@ -0,0 +1,71 @@
+// Example 2 — Weather Station domain demo of Slice with Lambda (C#)
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+//
+// Cast (Head First Design Patterns Weather Station, reduced):
+//   LightSensor      — hardware-ish dependency. Read() returns a byte.
+//   SunExposure      — enum. Reading > 128 => Sunny, otherwise Shady.
+//   WateringDuration — enum. None / Medium / Short.
+//                      (Long is YAGNI until the for-loop version of this
+//                      exercise exists.)
+//   SprinklerController — the client. Owns the _wateredToday flag, so the
+//                      guard is about client state, not sensor state.
+
+using System;
+
+public enum SunExposure
+{
+    Shady,
+    Sunny
+}
+
+public enum WateringDuration
+{
+    None,
+    Medium,
+    Short
+}
+
+public class LightSensor
+{
+    private readonly Random _rng = new Random();    // stand-in for hardware noise
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(256);
+    }
+}
+
+public class SprinklerController
+{
+    private readonly LightSensor _lightSensor;
+    private bool _wateredToday;                     // event-style client state
+
+    public SprinklerController(LightSensor lightSensor)
+    {
+        _lightSensor = lightSensor;
+    }
+
+    public WateringDuration ScheduleWatering()
+    {
+        if (_wateredToday)                          // guard: client state, stays
+        {
+            return WateringDuration.None;
+        }
+
+        _wateredToday = true;                       // set only after watering
+        byte reading = _lightSensor.Read();         // middle: unwanted dependency
+        SunExposure exposure = ToSunExposure(reading);
+        if (exposure == SunExposure.Sunny)          // tail: complex behaviour below
+        {                                           // the extraction point
+            return WateringDuration.Medium;
+        }
+        return WateringDuration.Short;
+    }
+
+    private static SunExposure ToSunExposure(byte reading)
+    {
+        return reading > 128 ? SunExposure.Sunny : SunExposure.Shady;
+    }
+}

ideas/slice-with-lambda/exercise/csharp/solution/IceCreamShopSolution.cs

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+// Example 3 solution — Ice cream shop demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3). The constructor now takes the lambda directly,
+// so tests construct with new IceCreamShop(() => 30).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public enum Warmth
+{
+    Cold,
+    Warm
+}
+
+public enum ThawAmount
+{
+    None,
+    Medium,
+    Low
+}
+
+public class Thermometer
+{
+    private readonly Random _rng = new Random();    // stand-in for the hardware
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(50);                 // raw sensor value
+    }
+}
+
+public class IceCreamShop
+{
+    private readonly Func<byte> _readTemperature;   // the thermometer, as a lambda
+    private bool _thawedToday;                      // event-style client state
+
+    public IceCreamShop(Func<byte> readTemperature)
+    {
+        _readTemperature = readTemperature;
+    }
+
+    public ThawAmount ThawStock()
+    {
+        Func<byte> readTemperature = () => _readTemperature();  // lambda at the top
+        return ThawStockTail(readTemperature);      // pass the lambda on
+    }
+
+    private ThawAmount ThawStockTail(Func<byte> readTemperature)
+    {
+        if (_thawedToday)                           // guard: client state, stays
+        {
+            return ThawAmount.None;
+        }
+
+        _thawedToday = true;                        // set only after thawing
+        byte temperature = readTemperature();       // middle: the stubbed lambda
+        Warmth warmth = ToWarmth(temperature);
+        if (warmth == Warmth.Warm)                  // tail: complex behaviour below
+        {                                           // the extraction point
+            return ThawAmount.Medium;
+        }
+        return ThawAmount.Low;
+    }
+
+    private static Warmth ToWarmth(byte temperature)
+    {
+        return temperature > 25 ? Warmth.Warm : Warmth.Cold;
+    }
+}

ideas/slice-with-lambda/exercise/csharp/solution/MetaphorFreeSolution.cs

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+// Example 1 solution — Metaphor-free demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3), overload seam added (step 3b), b inlined
+// (final cleanup).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public class Calculator
+{
+    private readonly SomeDependency _someDependency;
+
+    public Calculator(SomeDependency someDependency)
+    {
+        _someDependency = someDependency;
+    }
+
+    public int Calculate(int a)                          // overload: callers unchanged
+    {
+        return Calculate(a, a =>
+            _someDependency.mightThrowWhenPreconditionNotSatisfied(a));
+    }                                                    //   the real λ, baked into the head
+
+    public int Calculate(int a, Func<int, int> readB)    // the seam: λ is a parameter
+    {
+        if (a < 0) return 0;                             // guard clause: stays
+        return CalculateTail(a, readB);
+    }
+
+    private int CalculateTail(int a, Func<int, int> readB)
+    {
+        int c = a + readB(a);                            // b inlined
+        return c * 2;
+    }
+}
+
+public class SomeDependency
+{
+    private readonly Random _rng = new Random();    // stand-in for unpredictable computation
+
+    public int mightThrowWhenPreconditionNotSatisfied(int a)
+    {
+        if (a > 99)
+        {
+            throw new InvalidOperationException("precondition not satisfied");
+        }
+        return _rng.Next(100);
+    }
+}

ideas/slice-with-lambda/exercise/csharp/solution/SliceWithLambdaTests.cs

@@ -0,0 +1,82 @@
+// Tests for the three Slice-with-Lambda solutions — step 4: the lambda as a stub.
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+using Xunit;
+
+public class SliceWithLambdaTests
+{
+    // --- Example 1: metaphor-free (Calculator) ---
+
+    [Fact]
+    public void Guards_against_negative_input()
+    {
+        var calc = new Calculator(new SomeDependency());  // the real, flaky one...
+        Assert.Equal(0, calc.Calculate(-1, a => 42));     // ...never asked: stub not invoked
+    }
+
+    [Fact]
+    public void Throws_when_precondition_not_satisfied()
+    {
+        var calc = new Calculator(new SomeDependency());
+        Assert.Throws<InvalidOperationException>(
+            () => calc.Calculate(7, a => throw new InvalidOperationException()));
+    }
+
+    [Fact]
+    public void Combines_input_and_the_stubbed_value()
+    {
+        var calc = new Calculator(new SomeDependency());
+        Assert.Equal(84, calc.Calculate(0, a => 42));     // stub through the seam
+    }
+
+    // --- Example 2: Weather Station (SprinklerController) ---
+
+    [Fact]
+    public void Skips_watering_when_already_watered()
+    {
+        var controller = new SprinklerController(() => 200);  // pure lambda: no sensor
+        controller.ScheduleWatering();                        // water once...
+        Assert.Equal(WateringDuration.None, controller.ScheduleWatering());
+    }
+
+    [Fact]
+    public void Waters_longer_in_full_sun()
+    {
+        var controller = new SprinklerController(() => 200);  // sunny: > 128
+        Assert.Equal(WateringDuration.Medium, controller.ScheduleWatering());
+    }
+
+    [Fact]
+    public void Waters_less_in_the_shade()
+    {
+        var controller = new SprinklerController(() => 10);   // shady: ≤ 128
+        Assert.Equal(WateringDuration.Short, controller.ScheduleWatering());
+    }
+
+    // --- Example 3: Ice Cream Shop (IceCreamShop) ---
+
+    [Fact]
+    public void Skips_thawing_when_already_thawed()
+    {
+        var shop = new IceCreamShop(() => 30);        // pure lambda: no freezer
+        shop.ThawStock();                             // thaw once...
+        Assert.Equal(ThawAmount.None, shop.ThawStock());
+    }
+
+    [Fact]
+    public void Thaws_more_when_warm()
+    {
+        var shop = new IceCreamShop(() => 30);        // warm: > 25
+        Assert.Equal(ThawAmount.Medium, shop.ThawStock());
+    }
+
+    [Fact]
+    public void Thaws_less_when_cold()
+    {
+        var shop = new IceCreamShop(() => 5);         // cold: ≤ 25
+        Assert.Equal(ThawAmount.Low, shop.ThawStock());
+    }
+}

ideas/slice-with-lambda/exercise/csharp/solution/WeatherStationSolution.cs

@@ -0,0 +1,72 @@
+// Example 2 solution — Weather Station domain demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3). The constructor now takes the lambda directly,
+// so tests construct with new SprinklerController(() => 200).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public enum SunExposure
+{
+    Shady,
+    Sunny
+}
+
+public enum WateringDuration
+{
+    None,
+    Medium,
+    Short
+}
+
+public class LightSensor
+{
+    private readonly Random _rng = new Random();    // stand-in for hardware noise
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(256);
+    }
+}
+
+public class SprinklerController
+{
+    private readonly Func<byte> _readLight;         // the sensor, as a lambda
+    private bool _wateredToday;                     // event-style client state
+
+    public SprinklerController(Func<byte> readLight)
+    {
+        _readLight = readLight;
+    }
+
+    public WateringDuration ScheduleWatering()
+    {
+        Func<byte> readLight = () => _readLight();  // lambda definition at the top
+        return ScheduleWateringTail(readLight);     // pass the lambda on
+    }
+
+    private WateringDuration ScheduleWateringTail(Func<byte> readLight)
+    {
+        if (_wateredToday)                          // guard: client state, stays
+        {
+            return WateringDuration.None;
+        }
+
+        _wateredToday = true;                       // set only after watering
+        byte reading = readLight();                 // middle: the stubbed lambda
+        SunExposure exposure = ToSunExposure(reading);
+        if (exposure == SunExposure.Sunny)          // tail: complex behaviour below
+        {                                           // the extraction point
+            return WateringDuration.Medium;
+        }
+        return WateringDuration.Short;
+    }
+
+    private static SunExposure ToSunExposure(byte reading)
+    {
+        return reading > 128 ? SunExposure.Sunny : SunExposure.Shady;
+    }
+}