Test it

.gitignore

@@ -4,3 +4,4 @@ obj/
 riderModule.iml
 /_ReSharper.Caches/
 .idea/
+*.user

FicroKanSharp.Test/FicroKanSharp.Test.fsproj

@@ -5,12 +5,13 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <Compile Include="UnitTest1.fs" />
+        <Compile Include="TestExamples.fs" />
     </ItemGroup>
 
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
         <PackageReference Include="xunit" Version="2.4.1" />
+        <PackageReference Include="FsUnit" Version="4.1.0" />
         <PackageReference Include="NUnit3TestAdapter" Version="4.0.0" />
     </ItemGroup>
 

FicroKanSharp.Test/TestExamples.fs

@@ -0,0 +1,133 @@
+namespace FicroKanSharp.Test
+
+open FicroKanSharp
+open Xunit
+open FsUnitTyped
+
+module TestThing =
+
+    [<Fact>]
+    let ``Example from the docs`` () : unit =
+        let aAndB =
+            Goal.conj
+                (Goal.callFresh (fun x -> Goal.equiv (Term.Variable x) (Term.Literal 7)))
+                (Goal.callFresh (fun x -> Goal.disj (Goal.equiv (Term.Variable x) (Term.Literal 5)) (Goal.equiv (Term.Variable x) (Term.Literal 6))))
+
+        let u = Goal.evaluate aAndB State.empty
+        match u |> Stream.peel with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual
+            [
+                Variable.VariableCount 0, Term.Literal 7
+                Variable.VariableCount 1, Term.Literal 5
+            ]
+
+        match rest |> Stream.peel with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual
+            [
+                Variable.VariableCount 0, Term.Literal 7
+                Variable.VariableCount 1, Term.Literal 6
+            ]
+
+        match rest |> Stream.peel with
+        | None -> ()
+        | Some s -> failwith $"{s}"
+
+    [<Fact>]
+    let ``Another example`` () =
+        let aAndB =
+            (Goal.callFresh (fun x -> Goal.equiv (Term.Variable x) (Term.Literal 5)))
+
+        let u = Goal.evaluate aAndB State.empty
+        match u |> Stream.peel with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+        match Stream.peel rest with
+        | None -> ()
+        | Some s -> failwithf $"{s}"
+
+    [<Fact>]
+    let ``Recursive example`` () =
+        let rec fives (x : Variable) =
+            (Goal.disj (Goal.equiv (Term.Variable x) (Term.Literal 5)) (Goal.delay (fun () -> fives x)))
+
+        let u = Goal.evaluate (Goal.callFresh fives) State.empty
+        match u |> Stream.peel with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+        match Stream.peel rest with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+        match Stream.peel rest with
+        | None -> failwith "oh no"
+        | Some (s, _rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+    [<Fact>]
+    let ``Another recursive example`` () =
+        let rec fives (x : Variable) =
+            (Goal.disj (Goal.equiv (Term.Variable x) (Term.Literal 5)) (Goal.delay (fun () -> fives x)))
+        let rec sixes (x : Variable) =
+            (Goal.disj (Goal.equiv (Term.Variable x) (Term.Literal 6)) (Goal.delay (fun () -> sixes x)))
+        let fivesAndSixes =
+            Goal.callFresh (fun x -> Goal.disj (fives x) (sixes x))
+
+        let u = Goal.evaluate fivesAndSixes State.empty
+        match u |> Stream.peel with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+        match Stream.peel rest with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 6]
+
+        match Stream.peel rest with
+        | None -> failwith "oh no"
+        | Some (s, rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 5]
+
+        match Stream.peel rest with
+        | None -> failwith "oh no"
+        | Some (s, _rest) ->
+
+        s
+        |> Map.toList
+        |> shouldEqual [Variable.VariableCount 0, Term.Literal 6]

FicroKanSharp.Test/UnitTest1.fs

@@ -1,10 +0,0 @@
-namespace FicroKanSharp.Test
-
-open FicroKanSharp
-open Xunit
-
-module TestThing =
-
-    [<Fact>]
-    let ``Foo`` () : unit =
-        failwith "TODO!"

FicroKanSharp/AssemblyInfo.fs

@@ -0,0 +1,6 @@
+module AssemblyInfo
+
+open System.Runtime.CompilerServices
+
+[<assembly: InternalsVisibleTo("FicroKanSharp.Test")>]
+do()

FicroKanSharp/Domain.fs

@@ -1,6 +1,6 @@
 namespace FicroKanSharp
 
-type Variable = private | VariableCount of int
+type Variable = internal | VariableCount of int
 
 [<RequireQualifiedAccess>]
 module private Variable =
@@ -16,9 +16,10 @@ type Goal =
     | Disj of Goal * Goal
     | Conj of Goal * Goal
     | Fresh of (Variable -> Goal)
+    | Delay of (unit -> Goal)
 
 type State =
-    private
+    internal
         {
             Substitution : Map<Variable, Term>
             VariableCounter : Variable
@@ -56,11 +57,19 @@ module Stream =
         | Stream.Nonempty (fst, rest) ->
             mplus (g fst) (bind rest g)
 
+    let rec peel (s : Stream) : (Map<Variable, Term> * Stream) option =
+        match s with
+        | Stream.Empty -> None
+        | Stream.Nonempty (fst, rest) -> Some (fst.Substitution, rest)
+        | Stream.Procedure p -> peel (p ())
+
 [<RequireQualifiedAccess>]
 module Goal =
     let callFresh (f : Variable -> Goal) =
         Goal.Fresh f
 
+    let delay g = Goal.Delay g
+
     let disj (goal1 : Goal) (goal2 : Goal) : Goal =
         Goal.Disj (goal1, goal2)
 
@@ -117,4 +126,6 @@ module Goal =
         | Goal.Disj (goal1, goal2) ->
             Stream.mplus (evaluate goal1 state) (evaluate goal2 state)
         | Goal.Conj (goal1, goal2) ->
-            Stream.bind (evaluate goal1 state) (evaluate goal2)
+            Stream.bind (evaluate goal1 state) (evaluate goal2)
+        | Goal.Delay g ->
+            Stream.Procedure (fun () -> evaluate (g ()) state)

FicroKanSharp/FicroKanSharp.fsproj

@@ -7,6 +7,7 @@
 
     <ItemGroup>
         <Compile Include="Domain.fs" />
+        <Compile Include="AssemblyInfo.fs" />
     </ItemGroup>
 
 </Project>