fix the problem of the previous commit by reducing the stack usage

interpreter/code.c

@@ -13,29 +13,40 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
 
     while(1)
     {
+        assert(stack_top_a < STACK_SIZE_A);
+        
         switch (expr->type) {
         case CT_LIT:
-            prepare_return(root_frame_ptr, 
-                    updateT(target, &((LitEntry*) expr)->thunk));
+            set_return(root_frame_ptr, updateT(target, &((LitEntry*) expr)->thunk));
+            destroy_stack_frame(root_frame_ptr);
             return;
         case CT_VAR:
             if (expr->local_type == VAR_LOCAL) {
                 Thunk* thunk = forward_to(target, local(frame_ptr, ((VarEntry*) expr)->index));
+                
+                // Destroy stack frame before eval, it is not needed any more
+                // Greatly reduces stack usage
+                destroy_stack_frame(root_frame_ptr);                        
+                
+                // TODO: inline eval
                 if(force) thunk = eval(thunk);
-                prepare_return(root_frame_ptr, thunk);
+                
+                set_return(root_frame_ptr, thunk);
                 return;
             }else{
+                // Safe to destroy, the next call has no arguments
+                destroy_stack_frame(root_frame_ptr);
+                
                 Desc* slice = get_slice(((VarEntry*) expr)->f, 0);
                 
-                if(force &&  slice->type == FT_FUN)
+                if(force && slice->type == FT_FUN)
                 {
                     expr = ((FunEntry*)slice)->body;
                     continue;
                 }
                 else
                 {                    
-                    prepare_return(root_frame_ptr, 
-                            updateF(target, get_slice(((VarEntry*) expr)->f, 0)));
+                    set_return(root_frame_ptr, updateF(target, slice));
                     return;
                 }
             }
@@ -48,6 +59,8 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
 
             if (var->base.local_type == VAR_LOCAL) 
             {
+                // TODO: force
+                
                 Thunk* basethunk = eval(local(frame_ptr, var->index));
 
                 Desc* slice =
@@ -68,7 +81,8 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
                     thunk->_args[basethunk->desc->arity + i] = pop_a();
                 }
 
-                prepare_return(root_frame_ptr, thunk);
+                set_return(root_frame_ptr, thunk);
+                destroy_stack_frame(root_frame_ptr);
                 return;
             }
             else
@@ -83,9 +97,9 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
                         exec(((AppEntry*) expr)->args[i], frame_ptr, stack_top_a, &args[i], true);
                     }
 
-                    prepare_return(root_frame_ptr, 
+                    set_return(root_frame_ptr, 
                             ((PrimEntry*) slice)->exec(target));
-                    
+                    destroy_stack_frame(root_frame_ptr);
                     return;
                 }
                 else if (force && slice->type == FT_FUN) {
@@ -96,7 +110,7 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
                         push_a(NULL);
                         exec(((AppEntry*) expr)->args[i], frame_ptr, stack_top_a, NULL, is_strict_fun_arg((FunEntry*) slice, i));
                     }
-
+                    
                     expr = ((FunEntry*) slice)->body;
                     frame_ptr = new_frame_ptr;
                     continue;
@@ -112,7 +126,8 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr, Thunk* target, bool for
                         thunk->_args[i] = pop_a();
                     }
                     
-                    prepare_return(root_frame_ptr, thunk);
+                    set_return(root_frame_ptr, thunk);
+                    destroy_stack_frame(root_frame_ptr);
                     return;                    
                 }
             }

interpreter/main.c

@@ -29,7 +29,7 @@ int main ( int argc, char *argv[] )
     init_desc();
     init_prim();
 
-    char* input = "..\\tests\\Braun.bsapl";
+    char* input = "..\\tests\\nfib.bsapl";
     
     if ( argc == 2 )
     {

interpreter/mem.h

@@ -14,7 +14,8 @@ extern Thunk* stack_a[STACK_SIZE_A];
 #define push_a(r) stack_a[stack_top_a++]=(r)
 
 #define local(base, idx) stack_a[base+idx-1]
-#define prepare_return(base, r) stack_a[base-1]=(r); stack_top_a = base
+#define set_return(base, r) stack_a[base-1]=(r)
+#define destroy_stack_frame(base) stack_top_a = base
 
 void init_mem();
 void print_stat();