Added F# starter solution based on .NET Core

fsharp-core/GildedRose/GildedRose.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Update="FSharp.Core" Version="4.6.2" />
+  </ItemGroup>
+
+</Project>

fsharp-core/GildedRose/Program.fs

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+namespace GildedRose
+
+open System.Collections.Generic
+
+type Item = { Name: string; SellIn: int; Quality: int }
+
+type GildedRose(items:IList<Item>) =
+    let Items = items
+
+    member this.UpdateQuality() =
+        for i = 0 to Items.Count - 1 do
+            if Items.[i].Name <> "Aged Brie" && Items.[i].Name <> "Backstage passes to a TAFKAL80ETC concert" then
+                if Items.[i].Quality > 0 then
+                    if Items.[i].Name <> "Sulfuras, Hand of Ragnaros" then
+                        Items.[i] <- { Items.[i] with Quality = (Items.[i].Quality - 1) } 
+            else
+               if Items.[i].Quality < 50 then
+                    Items.[i] <- { Items.[i] with Quality = (Items.[i].Quality + 1) } 
+                    if Items.[i].Name = "Backstage passes to a TAFKAL80ETC concert" then
+                        if Items.[i].SellIn < 11 then
+                            if Items.[i].Quality < 50 then
+                                Items.[i] <- { Items.[i] with Quality = (Items.[i].Quality + 1) } 
+                        if Items.[i].SellIn < 6 then
+                            if Items.[i].Quality < 50 then
+                                Items.[i] <- { Items.[i] with Quality = (Items.[i].Quality + 1) } 
+            if Items.[i].Name <> "Sulfuras, Hand of Ragnaros" then                 
+                Items.[i] <- { Items.[i] with SellIn  = (Items.[i].SellIn - 1) } 
+            if Items.[i].SellIn < 0 then
+                if Items.[i].Name <> "Aged Brie" then
+                    if Items.[i].Name <> "Backstage passes to a TAFKAL80ETC concert" then
+                        if Items.[i].Quality > 0 then
+                            if Items.[i].Name <> "Sulfuras, Hand of Ragnaros" then
+                                Items.[i] <- { Items.[i] with Quality   = (Items.[i].Quality  - 1) } 
+                    else
+                        Items.[i] <- { Items.[i] with Quality   = (Items.[i].Quality  - Items.[i].Quality) } 
+                else
+                    if Items.[i].Quality < 50 then
+                        Items.[i] <- { Items.[i] with Quality   = (Items.[i].Quality + 1) }  
+        ()
+
+
+module Program =
+    [<EntryPoint>]
+    let main argv =
+        printfn "OMGHAI!"
+        let Items = new List<Item>()
+        Items.Add({Name = "+5 Dexterity Vest"; SellIn = 10; Quality = 20})
+        Items.Add({Name = "Aged Brie"; SellIn = 2; Quality = 0})
+        Items.Add({Name = "Elixir of the Mongoose"; SellIn = 5; Quality = 7})
+        Items.Add({Name = "Sulfuras, Hand of Ragnaros"; SellIn = 0; Quality = 80})
+        Items.Add({Name = "Sulfuras, Hand of Ragnaros"; SellIn = -1; Quality = 80})
+        Items.Add({Name = "Backstage passes to a TAFKAL80ETC concert"; SellIn = 15; Quality = 20})
+        Items.Add({Name = "Backstage passes to a TAFKAL80ETC concert"; SellIn = 10; Quality = 49})
+        Items.Add({Name = "Backstage passes to a TAFKAL80ETC concert"; SellIn = 5; Quality = 49})
+        Items.Add({Name = "Conjured Mana Cake"; SellIn = 3; Quality = 6})
+
+        let app = new GildedRose(Items)
+        for i = 0 to 30 do
+            printfn "-------- day %d --------" i
+            printfn "name, sellIn, quality"
+            for j = 0 to Items.Count - 1 do
+                 printfn "%s, %d, %d" Items.[j].Name Items.[j].SellIn Items.[j].Quality
+            printfn ""
+            app.UpdateQuality()
+        0