inline eval when an argument is returned in the spine such tail call elimination

can be applied.

interpreter/code.c

@@ -170,12 +170,42 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr)
         }            
         case CT_VAR:
             if (expr->local_type == VAR_LOCAL) {
-                Thunk* thunk = forward_to(get_dst(root_frame_ptr), local(frame_ptr, ((VarEntry*) expr)->index));
+                Thunk* thunk = local(frame_ptr, ((VarEntry*) expr)->index);
+                                
+                while (thunk->desc == (Desc*) __FORWARD_PTR__) {
+                    thunk = thunk->_forward_ptr;
+                }
+
+                forward_to(get_dst(root_frame_ptr), thunk);
+                set_return(root_frame_ptr, thunk);
+                
+                if (thunk->desc->type == FT_FUN) {
+                    
+                    // Destroy stack frame before eval, it is not needed any more
+                    // Greatly reduces stack usage
+                    destroy_stack_frame(root_frame_ptr);                    
+                    frame_ptr = stack_top_a;
+                    // Here frame_ptr == root_frame_ptr
+                    
+                    for (int i = 0; i < thunk->desc->arity; i++) {
+                        // TODO: handle strictness
+                        push_a(thunk->_args[i]);
+                    }
+                    
+                    expr = ((FunEntry*) thunk->desc)->body;
+                    continue;
+                }
+                else if(thunk->desc->type == FT_PRIM) {
+
+                    for (int i = 0; i < thunk->desc->arity; i++) {
+                        // TODO: handle strictness
+                        push_a(thunk->_args[i]);
+                    }
+
+                    ((PrimEntry*) thunk->desc)->exec(root_frame_ptr);
+                }                
                 
-                // Destroy stack frame before eval, it is not needed any more
-                // Greatly reduces stack usage
                 destroy_stack_frame(root_frame_ptr);
-                set_return(root_frame_ptr, eval(thunk));
                 return;
             }else{
                 // Safe to destroy, the next call has no arguments

interpreter/desc.c

@@ -92,8 +92,10 @@ void init_desc() {
     __REAL__ = alloc_prim("REAL");
     __STRING__ = alloc_prim("STRING");
     __ARRAY__ = alloc_prim("ARRAY");
+    __FORWARD_PTR__ = alloc_prim("FWD");
 }
 
+struct FunEntry* __FORWARD_PTR__;
 struct FunEntry* __INT__;
 struct FunEntry* __BOOL__;
 struct FunEntry* __CHAR__;

interpreter/desc.h

@@ -69,6 +69,7 @@ bool is_strict_fun_arg(FunEntry* f, int nr_arg);
 
 int printDesc(Desc* f);
 
+extern struct FunEntry* __FORWARD_PTR__;
 extern struct FunEntry* __INT__;
 extern struct FunEntry* __BOOL__;
 extern struct FunEntry* __CHAR__;

interpreter/thunk.c

@@ -17,12 +17,11 @@ Thunk* forward_to(Thunk* target, Thunk* thunk) {
     assert(thunk != NULL); 
     
     if (target != NULL) {
-        target->desc = NULL;
+        target->desc = (Desc*) __FORWARD_PTR__;
         target->_forward_ptr = thunk;
-        return thunk;
-    } else {
-        return thunk;
-    }
+    } 
+        
+    return thunk;
 }
 
 int thunk_size(Thunk* thunk) {
@@ -117,7 +116,7 @@ struct Thunk* updateF(Thunk* target, Desc* f) {
 struct Thunk* eval(Thunk* thunk) {
     assert(thunk != NULL);    
     
-    while (thunk->desc == NULL) {
+    while (thunk->desc == (Desc*) __FORWARD_PTR__) {
         thunk = thunk->_forward_ptr;
     }
 
@@ -150,7 +149,7 @@ struct Thunk* eval(Thunk* thunk) {
 }
 
 void print(Thunk* thunk, bool force) {
-    while (thunk->desc == NULL) {
+    while (thunk->desc == (Desc*) __FORWARD_PTR__) {
         thunk = thunk->_forward_ptr;
     }