Move Writer Functions to Serefa

Move the `display` and `newline` builtins to the Serefa library. Here
we can hopefully extend them with better support for displaying external
representation and add a `write` impl too.

src/Feersum/Builtins.fs

@@ -165,74 +165,6 @@ let private createBuiltins (assm: AssemblyDefinition) (ty: TypeDefinition) =
 
         meth
 
-    /// Display builtin. This is intended for user-readable output rather than
-    /// any machine readable round tripping. Printing out strings & chars should
-    /// display their raw form. All other objects is up to the implementation.
-    /// 
-    /// This implementation calls `ToString` on the underlying .NET object and
-    /// uses that directly.
-    let displayBuiltin =
-        let meth, il = declareBuiltinMethod "display"
-        let fail = il.Create(OpCodes.Nop)
-        let hasValue = il.Create(OpCodes.Nop)
-        let print = il.Create(OpCodes.Dup)
-
-        il.Emit(OpCodes.Ldarg_0)
-        il.Emit(OpCodes.Ldlen)
-        il.Emit(OpCodes.Ldc_I4_1)
-        il.Emit(OpCodes.Bne_Un, fail)
-
-        // null check
-        il.Emit(OpCodes.Ldarg_0)
-        il.Emit(OpCodes.Ldc_I4_0)
-        il.Emit(OpCodes.Ldelem_Ref)
-        il.Emit(OpCodes.Brtrue_S, hasValue)
-
-        // If null use empty string
-        il.Emit(OpCodes.Ldstr, "")
-        il.Emit(OpCodes.Br, print)
-
-        // convert to string
-        il.Append(hasValue)
-        let toStr = typeof<obj>.GetMethod("ToString", BindingFlags.Public ||| BindingFlags.Instance)
-        let toStr = assm.MainModule.ImportReference toStr
-        il.Emit(OpCodes.Ldarg_0)
-        il.Emit(OpCodes.Ldc_I4_0)
-        il.Emit(OpCodes.Ldelem_Ref)
-        il.Emit(OpCodes.Callvirt, toStr)
-
-        il.Append(print)
-
-        let write = typeof<Console>.GetMethod("Write", [| typeof<string> |])
-        let write = assm.MainModule.ImportReference write
-        il.Emit(OpCodes.Call, write)
-        il.Emit(OpCodes.Ret)
-
-        il.Append(fail)
-        emitThrow il assm "`dsiplay` expects a single argument"
-
-        meth
-
-    let newlineBuiltin =
-        let meth, il = declareBuiltinMethod "newline"
-        let fail = il.Create(OpCodes.Nop)
-
-        il.Emit(OpCodes.Ldarg_0)
-        il.Emit(OpCodes.Ldlen)
-        il.Emit(OpCodes.Ldc_I4_0)
-        il.Emit(OpCodes.Bne_Un, fail)
-
-        let write = typeof<Console>.GetMethod("WriteLine", [| |])
-        let write = assm.MainModule.ImportReference write
-        il.Emit(OpCodes.Call, write)
-        il.Emit(OpCodes.Ldnull)
-        il.Emit(OpCodes.Ret)
-
-        il.Append(fail)
-        emitThrow il assm "`newline` expects no arguments"
-
-        meth
-
     [ ("+", createArithBuiltin "arithadd" OpCodes.Add 0.0)
     ; ("-", createArithBuiltin "arithsub" OpCodes.Sub 0.0)
     ; ("/", createArithBuiltin "arithdiv" OpCodes.Div 1.0)
@@ -241,9 +173,7 @@ let private createBuiltins (assm: AssemblyDefinition) (ty: TypeDefinition) =
     ; (">", createCompBuiltin "arithgt" OpCodes.Bgt)
     ; ("<", createCompBuiltin "arithlt" OpCodes.Blt)
     ; (">=", createCompBuiltin "arithgte" OpCodes.Bge)
-    ; ("<=", createCompBuiltin "arithlte" OpCodes.Ble)
-    ; ("newline", newlineBuiltin)
-    ; ("display", displayBuiltin) ]
+    ; ("<=", createCompBuiltin "arithlte" OpCodes.Ble) ]
     |> Seq.map(fun (name, method) -> (name, method :> MethodReference))
     |> Map.ofSeq
 

src/Serehfa/ArgHelpers.cs

@@ -4,6 +4,16 @@ namespace Serehfa
 {
     public class ArgHelpers
     {
+        public static void CheckNoArgs(object[] args)
+        {
+            if (args.Length != 0)
+            {
+                throw new ArgumentException(
+                    $"Expected no arguments, but received {args.Length}",
+                    nameof(args));
+            }
+        }
+
         public static T UnpackArgs<T>(object[] args)
         {
             if (args.Length != 1)

src/Serehfa/Undefined.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace Serehfa
+{
+    /// <summary>
+    ///  The unspecified / undefined value. Instances of this type are returned
+    ///  from scheme functions where no specific return value is specified in
+    ///  the standard.
+    /// </summary>
+    public class Undefined
+    {
+        private static Lazy<Undefined> s_Instance = new Lazy<Undefined>();
+        public static Undefined Instance => s_Instance.Value;
+
+        public override string ToString() => "; Unspecified value";
+
+        /// <summary>
+        ///  Instances of these values are never equal to anything else.
+        /// </summary>
+        public override bool Equals(object obj) => false;
+
+        public override int GetHashCode() => base.GetHashCode();
+    }
+}

src/Serehfa/Write.cs

@@ -0,0 +1,39 @@
+namespace Serehfa
+{
+    using System;
+    using static ArgHelpers;
+
+    public static class Write
+    {
+        [LispBuiltin("newline")]
+        public static object Newline(object[] args)
+        {
+            CheckNoArgs(args);
+
+            Console.WriteLine();
+
+            return Undefined.Instance;
+        }
+
+        /// <summary>
+        /// Display builtin. This is intended for user-readable output rather than
+        /// any machine readable round tripping. Printing out strings &amp; chars should
+        /// display their raw form. All other objects is up to the implementation.
+        /// 
+        /// This implementation calls `ToString` on the underlying .NET object and
+        /// uses that directly.
+        /// </summary>
+        [LispBuiltin("display")]
+        public static object Display(object[] args)
+        {
+            var obj = UnpackArgs<object>(args);
+
+            var repr = obj == null ?
+                "'()" : obj.ToString();
+
+            Console.Write(repr);
+
+            return Undefined.Instance;
+        }
+    }
+}

test/Feersum.Tests/_snapshots/SpecTests_spec tests compile and run.json

@@ -70,7 +70,7 @@
     "Exit": 0
   },
   "display.scm": {
-    "Output": "\n\n123\n",
+    "Output": "\n'()\n123\n",
     "Error": "",
     "Exit": 0
   },
@@ -157,7 +157,7 @@
     "Exit": 0
   },
   "quotes.scm": {
-    "Output": "1\nhello world\n\n(1 2 3)\n1\nhello world\n\n(1 2 3)\n(quote (quote 123))\nd\n| |\n|test\\x9;ident|\n|hello world|\nTrue\n",
+    "Output": "1\nhello world\n'()\n(1 2 3)\n1\nhello world\n'()\n(1 2 3)\n(quote (quote 123))\nd\n| |\n|test\\x9;ident|\n|hello world|\nTrue\n",
     "Error": "",
     "Exit": 0
   },