From 693a1be718281e426e6c537a4389b3fc04dcb1a3 Mon Sep 17 00:00:00 2001
From: "Mike D. Lowis" <mike@mdlowis.com>
Date: Mon, 19 Mar 2012 16:53:14 -0400
Subject: [PATCH] Added prototype of continuations in C++

---
 lang_design/cont_gc/main.cpp | 113 +++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 lang_design/cont_gc/main.cpp

diff --git a/lang_design/cont_gc/main.cpp b/lang_design/cont_gc/main.cpp
new file mode 100644
index 0000000..a7754d4
--- /dev/null
+++ b/lang_design/cont_gc/main.cpp
@@ -0,0 +1,113 @@
+#include <list>
+#include <setjmp.h>
+#include <stdio.h>
+
+extern long* Stack_Bottom;
+extern long* Return_Value;
+
+class Continuation
+{
+    public:
+        int n;
+        long* stack;
+        jmp_buf registers;
+    public:
+        Continuation() : n(0), stack(0) {}
+        Continuation(long* pbos, long*ptos)
+        {
+            n = pbos-ptos;
+            stack = new long[n];
+            for (int i = 0; i<n; ++i) {
+                stack[i] = pbos[-i];
+            }
+        }
+        ~Continuation()
+        {
+            if(stack != 0) delete stack;
+        }
+
+        void operator () (long* ret_val)
+        {
+            Return_Value = ret_val;
+            (*this)(false);
+        }
+
+        void operator () (bool once_more)
+        {
+            long padding[12];
+            long tos;
+            int i,n;
+            if(stack != 0)
+            {
+                /*
+                 * Make sure there's enough room on the stack
+                 */
+                if ( (Stack_Bottom - n) < (&tos) ) {
+                    printf("Making room\n");
+                    (*this)(true);
+                    printf("Done making room\n");
+                }
+
+                if (once_more) {
+                    printf("Calling one more time\n");
+                    (*this)(false);
+                    printf("done calling one more time\n");
+                }
+
+                /*
+                 * Copy stack back out from continuation
+                 */
+                for (i = 0; i < n; ++i) {
+                    printf("copying byte\n");
+                    printf("%d\n",Stack_Bottom);
+                    Stack_Bottom[i] = stack[i];
+                    printf("done copying byte\n");
+                }
+            }
+            printf("jumping back\n");
+            longjmp(registers,1);
+        }
+};
+
+long* Stack_Bottom = 0;
+long* Return_Value = 0;
+std::list<Continuation*> Continuations;
+
+int save_context(Continuation* c)
+{
+    Continuations.push_back(c);
+    return setjmp(c->registers);
+}
+
+void restore_context(long* ret_val)
+{
+    Continuation* c = Continuations.back();
+    Continuations.pop_back();
+    printf("Jumping back to main\n");
+    (*c)(ret_val); // Call the continuation
+    printf("Should not print\n");
+}
+
+#define CALL_CC(a) if(! save_context( new Continuation() ) ) { a; }
+#define RETURN(a)  restore_context( (long*)a )
+
+void max(int a,int b)
+{
+    printf("beginning of max\n");
+    int* ret = new int;
+    *ret = (a > b) ? a : b;
+    printf("Before return\n");
+    RETURN( ret );
+    printf("This should never print\n");
+}
+
+int main(int argc, char** argv)
+{
+    long bottom;
+    Stack_Bottom = &bottom;
+    printf("%d\n", Stack_Bottom);
+    printf("Calling max\n");
+    CALL_CC( max(1,2); );
+    printf("Done calling max\n");
+    printf("%d\n",*Return_Value);
+}
-- 
2.49.0