Add Chapter 01 08.

src/FPinFSharp.App/Chapter_01/Chapter_01_08.fs

@@ -0,0 +1,9 @@
+namespace FPinFSharp.App.Chapter_01
+
+// 1.8 Euclid’s algorithm (for computing the greatest common divisor of two natural numbers).
+module Chapter_01_08 =
+
+    let rec gcd (m, n) =
+        match (m, n) with
+        | (0, n) -> n
+        | (m, n) -> gcd(n % m, m)

src/FPinFSharp.App/FPinFSharp.App.fsproj

@@ -13,6 +13,7 @@
     <Compile Include="Chapter_01\Chapter_01_04.fs" />
     <Compile Include="Chapter_01\Chapter_01_05.fs" />
     <Compile Include="Chapter_01\Chapter_01_06.fs" />
+    <Compile Include="Chapter_01\Chapter_01_08.fs" />
   </ItemGroup>
 
 </Project>

tests/FPinFSharp.App.UnitTests/Chapter_01/Chapter_01_06_Tests.fs

@@ -6,7 +6,7 @@ open Xunit
 module Chapter_01_06_Tests =
 
     [<Fact>]
-    let ``Should not throw an exception`` () =
+    let ``Should triple 10 to get 1000`` () =
         let x = 10
         let expectedResult = 1000
         let actualResult = validFunction x

tests/FPinFSharp.App.UnitTests/Chapter_01/Chapter_01_08_Tests.fs

@@ -0,0 +1,13 @@
+namespace FPinFSharp.App.UnitTests.Chapter_01
+
+open FPinFSharp.App.Chapter_01.Chapter_01_08
+open Xunit
+
+module Chapter_01_08_Tests =
+
+    [<Theory>]
+    [<InlineData(12, 27, 3)>]
+    [<InlineData(36, 116, 4)>]
+    let ``Should get the greatest common divisor of two natural numbers`` (m, n, expectedResult) =
+        let actualResult = gcd(m, n)
+        Assert.Equal(expectedResult, actualResult)

tests/FPinFSharp.App.UnitTests/FPinFSharp.App.UnitTests.fsproj

@@ -15,6 +15,7 @@
     <Compile Include="Chapter_01\Chapter_01_04_Tests.fs" />
     <Compile Include="Chapter_01\Chapter_01_05_Tests.fs" />
     <Compile Include="Chapter_01\Chapter_01_06_Tests.fs" />
+    <Compile Include="Chapter_01\Chapter_01_08_Tests.fs" />
   </ItemGroup>
 
   <ItemGroup>