introduce forward pointers in thunks

overwrite a thunk if the result fits or put a forward pointer there

interpreter/code.c

@@ -14,15 +14,7 @@ struct Thunk* exec(Code* expr, int frame_ptr, Thunk* target)
 			switch(expr->local_type)
 			{
 				case LIT_INT:
-					if(target == NULL)
-					{
-						return createI(((LitEntry*) expr)->_int);
-					}
-					else
-					{
-						updateI(target, ((LitEntry*) expr)->_int);
-						return target;
-					}	
+					return updateI(target, ((LitEntry*) expr)->_int);	
 				default:
 					printf("Exec: Unhandled LIT type");
 					exit(-1);
@@ -31,8 +23,8 @@ struct Thunk* exec(Code* expr, int frame_ptr, Thunk* target)
 		case CT_VAR:
 			switch(expr->local_type)
 			{
-				case VAR_FN:
-					return createF(((VarEntry*) expr)->f, 0);
+				case VAR_FN:		
+					return updateF(target, ((VarEntry*) expr)->f, 0);
 				case VAR_ARG:				
 					return stack[frame_ptr - ((VarEntry*) expr)->index];
 				default:
@@ -51,7 +43,7 @@ struct Thunk* exec(Code* expr, int frame_ptr, Thunk* target)
 			switch(var->base.local_type)
 			{
 				case VAR_FN:		
-					thunk = createF(var->f, expr->nr_args);
+					thunk = updateF(target, var->f, expr->nr_args);
 					for(int i=0; i<thunk->desc->arity; i++)
 					{
 						thunk->_args[i] = exec(((AppEntry*)expr)->args[i], frame_ptr, NULL);
@@ -61,7 +53,7 @@ struct Thunk* exec(Code* expr, int frame_ptr, Thunk* target)
 					Thunk* basethunk;
 					basethunk = eval(stack[frame_ptr - var->index]);
 					
-					thunk = createF(basethunk->desc->type == FT_SLICE ?
+					thunk = updateF(target, basethunk->desc->type == FT_SLICE ?
 						((SliceEntry*) basethunk->desc)->forward_ptr : basethunk->desc, basethunk->desc->arity + expr->nr_args);
 
 					for(int i=0; i<basethunk->desc->arity; i++)

interpreter/prim.c

@@ -8,7 +8,7 @@
 
 void __add(Thunk* target)
 {
-	return updateI(target, readI(eval(stack[stack_top - 2])) + readI(eval(stack[stack_top - 1])));
+	updateI(target, readI(eval(stack[stack_top - 2])) + readI(eval(stack[stack_top - 1])));
 }
 
 PrimEntry* add_prim(int arity, int strictness, char* name, void (*exec)(Thunk*))

interpreter/thunk.c

@@ -6,19 +6,37 @@
 #include "code.h"
 #include "mem.h"
 
-struct Thunk* createI(int i)
+#define max(a,b) \
+   ({ __typeof__ (a) _a = (a); \
+       __typeof__ (b) _b = (b); \
+     _a > _b ? _a : _b; })
+
+int thunk_size(Thunk* thunk)
 {
-	Thunk* thunk = (Thunk*) alloc_heap(sizeof(Thunk));
-	thunk->desc = (Desc*) __INT__;
-	thunk->_int = i;
-	return thunk;
+	if(thunk->desc == NULL || thunk->desc->type == FT_BOXED_LIT)
+	{
+		if(thunk->desc == (Desc*) __STRING__ || thunk->desc == (Desc*) __ARRAY__)
+		{
+			printf("tunk_size: unhandled literal type\n");
+			exit(-1);		
+		}
+
+		return sizeof(Thunk);
+	}
+	else
+	{
+		return max(sizeof(Thunk), sizeof(Desc*) + sizeof(Thunk*) * thunk->desc->arity);
+	}
 }
 
-void updateI(Thunk* target, int i)
+struct Thunk* updateI(Thunk* target, int i)
 {
+	if(target == NULL) target = (Thunk*) alloc_heap(sizeof(Thunk));
+	
 	// always can be overwritten with boxed integer
 	target->desc = (Desc*) __INT__;
 	target->_int = i;
+	return target;
 }
 
 int readI(Thunk* thunk)
@@ -32,10 +50,25 @@ int readI(Thunk* thunk)
 	return thunk->_int;
 }
 
-struct Thunk* createF(Desc* f, int nrargs)
+struct Thunk* updateF(Thunk* target, Desc* f, int nrargs)
 {
-	// Even if no arguments, still allocate enough space for a forward pointer 
-	Thunk* thunk = (Thunk*) alloc_heap(sizeof(Thunk) + sizeof(Thunk*) * (nrargs > 0 ? nrargs - 1 : 0));	
+	Thunk* thunk = target;
+	int newsize = max(sizeof(Thunk), sizeof(Desc*) + sizeof(Thunk*) * nrargs);
+	
+	if(thunk == NULL)
+	{
+		thunk = (Thunk*) alloc_heap(newsize);
+	}
+	else
+	{		
+		if(thunk_size(target) < newsize)
+		{
+			thunk = (Thunk*) alloc_heap(newsize);
+			target->desc = NULL;
+			target->_forward_ptr = thunk;
+		}
+	}
+	
 	thunk->desc = &(((SliceEntry*) f)[-(f->arity - nrargs)].base);
 	return thunk;
 }
@@ -43,6 +76,12 @@ struct Thunk* createF(Desc* f, int nrargs)
 Thunk* eval(Thunk* thunk)
 {
 	while(true){
+		
+		while(thunk->desc == NULL)
+		{
+			thunk =  thunk->_forward_ptr;
+		}
+		
 		switch(thunk->desc->type)
 		{
 			case FT_BOXED_LIT:
@@ -56,6 +95,7 @@ Thunk* eval(Thunk* thunk)
 			
 				for(int i=0; i<thunk->desc->arity; i++)
 				{
+					// TODO: handle strictness
 					pushs(thunk->_args[i]);
 				}
 				thunk = exec(((FunEntry*) thunk->desc)->body, stack_top - 1, thunk);
@@ -105,6 +145,11 @@ int printDesc(Desc* f)
 
 void print(Thunk* thunk)
 {
+	while(thunk->desc == NULL)
+	{
+		thunk =  thunk->_forward_ptr;
+	}	
+	
 	if(thunk->desc->type == FT_BOXED_LIT)
 	{
 		if((FunEntry*) thunk->desc == __INT__)

interpreter/thunk.h

@@ -6,11 +6,12 @@
 
 typedef struct Thunk
 {
-	struct Desc* desc;
+	struct Desc* desc; // NULL, if it is a forward pointer
 	union
 	{
+		Thunk* _forward_ptr;		
 		int _int;
-		double _real;	// TODO: move "real" out of here, too long 
+		double _real;	// TODO: move "real" out of here, too long (at least on 32 bits)
 		char _char;
 		int _bool;
 		struct CleanString* _string_ptr;
@@ -19,11 +20,10 @@ typedef struct Thunk
 	};
 } Thunk;
 
-struct Thunk* createI(int i);
-void updateI(Thunk* target, int i);
+struct Thunk* updateI(Thunk* target, int i);
 int readI(Thunk* thunk);
 
-struct Thunk* createF(Desc* f, int nrargs);
+struct Thunk* updateF(Thunk* target, Desc* f, int nrargs);
 
 Thunk* eval(Thunk* thunk);