Add call/cc support

README.md

@@ -39,7 +39,6 @@ It has most features that a language would support:
 
 Many Scheme features are not (yet) supported. Among those are:
 
-* continuation (`call/cc`)
 * use square brackets `[...]` in place of parenthesis `(...)`
 
 

src/schemy/Builtins.cs

@@ -49,6 +49,7 @@ public static IDictionary<Symbol, object> CreateBuiltins(Interpreter interpreter
             builtins[Symbol.FromString("null?")] = NativeProcedure.Create<object, bool>(x => x is List<object> && ((List<object>)x).Count == 0, "null?");
             builtins[Symbol.FromString("assert")] = new NativeProcedure(AssertImpl, "assert");
             builtins[Symbol.FromString("load")] = NativeProcedure.Create<string, None>(filename => LoadImpl(interpreter, filename), "load");
+			builtins[Symbol.FromString("call/cc")] = NativeProcedure.Create<ICallable, object>(Continuation.CallWithCurrentContinuation, "call/cc");
 
             return builtins;
         }

src/schemy/Continuation.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+namespace Schemy
+{
+	class Continuation : Exception
+	{
+		object Value { get; set; }
+		StackTrace Stack { get; set; }
+		Thread Thread { get; set; }
+
+		public static object CallWithCurrentContinuation(ICallable fc1)
+		{
+			var ccc = new Continuation { Stack = new StackTrace(), Thread = Thread.CurrentThread };
+			try
+			{
+				var exitproc = NativeProcedure.Create<object, object>(v =>
+						{
+							var f1 = new StackTrace().GetFrames();
+							var c1 = ccc.Stack.GetFrames();
+							var offset = f1.Length - c1.Length;
+							if (ccc.Thread == Thread.CurrentThread)
+							{
+								for (int i = c1.Length - 1; i >= 0; i--)
+								{
+									if (c1[i].GetMethod() != f1[i + offset].GetMethod())
+									{
+										throw new NotImplementedException("not supported, continuation called outside dynamic extent");
+									}
+								}
+							}
+							ccc.Value = v;
+							throw ccc;
+						});
+				return fc1.Call(new List<object> { exitproc });
+			}
+			catch (Continuation c)
+			{
+				if (ccc == c)
+				{
+					return c.Value;
+				}
+				else
+				{
+					throw;
+				}
+			}
+		}
+	}
+}

src/schemy/schemy.csproj

@@ -56,6 +56,7 @@
     <Compile Include="Symbol.cs" />
     <Compile Include="Utils.cs" />
     <EmbeddedResource Include="init.ss"><LogicalName>init.ss</LogicalName></EmbeddedResource>
+    <Compile Include="Continuation.cs" />
   </ItemGroup>
 
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />

src/test/tests.ss

@@ -114,6 +114,25 @@
       (* a b)))
   (assert (= 20 x)))
 
+(define (test-call/cc)
+  ; test call/cc
+  (assert 
+   (= 20 
+      (call/cc 
+       (lambda (k)
+        (* 5 4)))))
+  (assert
+   (= 4
+      (call/cc
+        (lambda (k)
+          (* 5 (k 4))))))
+  (assert
+   (= 6
+      (+ 2 (call/cc
+            (lambda (k)
+              (* 5 (k 4))))))))
+
+
 
 ;; =========
 ;; RUN TESTS
@@ -132,7 +151,7 @@
 (test-list)
 (test-syntax)
 (test-macro)
-
+(test-call/cc)
 
 ;; =======================
 ;; Interpreter integration