Result concept exercise (initial draft)

exercises/concept/family-recipes/.meta/Exemplar.fs

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+module FamilyRecipes
+
+type ValidationError = 
+| EmptyList
+| InvalidIngredientQuantity
+| MissingIngredientItem
+
+let parseInt (text: string) : Result<int, unit> =
+    let success, value = System.Int32.TryParse text
+    if success then Ok value else Error ()
+
+let splitOnce (text: string) (separator: char) : (string * string) option = 
+    match text.IndexOf(separator) with
+    | -1 -> None
+    | index -> Some (text.Substring(0, index), text.Substring(index + 1))
+
+let validateIngredient (text: string): Result<unit, ValidationError> =
+    match splitOnce text ' ' with
+    | Some (quantity, item) -> 
+        match parseInt quantity with
+        | Ok _ -> 
+            if item.Length = 0 then 
+                Error MissingIngredientItem
+            else
+                Ok ()
+        | Error _ -> Error InvalidIngredientQuantity
+    | _ -> Error MissingIngredientItem
+
+let validate (input: string) : Result<string, ValidationError> = 
+    let nonblankLines =
+        input.Split('\n')
+        |> Array.filter (fun l -> l.Length > 0)
+    if nonblankLines.Length = 0 then Error EmptyList
+    else
+        let firstError = 
+            nonblankLines
+            |> Array.map validateIngredient
+            |> Array.tryFind (fun r -> r.IsError)
+        match firstError with
+        | Some (Error error) -> Error error
+        | _ -> Ok input

exercises/concept/family-recipes/FamilyRecipes.fs

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+module FamilyRecipes
+
+type ValidationError = 
+| EmptyList
+| InvalidIngredientQuantity
+| MissingIngredientItem
+
+let parseInt (text: string) : Result<int, unit> =
+    let success, value = System.Int32.TryParse text
+    if success then Ok value else Error ()
+
+let validate input = 
+    failwith "Please implement this function"

exercises/concept/family-recipes/FamilyRecipes.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="FamilyRecipes.fs" />
+    <Compile Include="FamilyRecipesTests.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
+    <PackageReference Include="FsUnit.xUnit" Version="4.0.4" />
+  </ItemGroup>
+
+</Project>

exercises/concept/family-recipes/FamilyRecipesTests.fs

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+module Tests
+
+open FsUnit.Xunit
+open Xunit
+
+open FamilyRecipes
+
+[<Fact>]
+let ``Error on blank list`` () =
+    let expected: Result<string, ValidationError> = Error EmptyList
+    validate "" |> should equal expected
+
+[<Fact>]
+let ``Error on blank line`` () =
+    let expected: Result<string, ValidationError> = Error EmptyList
+    validate "\n" |> should equal expected
+
+[<Fact>]
+let ``Error on non-numeric ingredient quantity`` () =
+    let expected: Result<string, ValidationError> = Error InvalidIngredientQuantity
+    validate "foo bar" |> should equal expected
+
+[<Fact>]
+let ``Error on missing ingredient item`` () =
+    let expected: Result<string, ValidationError> = Error MissingIngredientItem
+    validate "24 " |> should equal expected
+
+[<Fact>]
+let ``Minimal valid list`` () =
+    let input = """1 cup rice"""
+    let expected: Result<string, ValidationError> = Ok input
+    validate input |> should equal expected
+
+[<Fact>]
+let ``Valid list with multiple ingredients`` () =
+    let input = """4 ounces of oatmeal
+12 ounces of water
+1 tablespoon of honey"""
+    let expected: Result<string, ValidationError> = Ok input
+    validate input |> should equal expected
+
+[<Fact>]
+let ``Blank lines within valid list are OK`` () =
+    let input = "1 foo\n2 bar"
+    let expected: Result<string, ValidationError> = Ok input
+    validate input |> should equal expected