Add and simplify environment representation

add simpler representation for environments in order to remove
red-black trees.

source/bootstrap.c

@@ -785,6 +785,85 @@ cherry_read(byte_t** src, byte_t* buffer, size_t buffer_size)
 // runtime utils
 // ----------------------------------------------------------------------------
 
+struct value*
+env_lookup(struct value* env, struct value* symbol)
+{
+	struct value *frame, *vars, *vals;
+
+	while(!IS_NULL(env)) {
+		frame = FIRST_FRAME(env);
+		vars = FRAME_VARIABLES(frame);
+		vals = FRAME_VALUES(frame);
+
+		while(!IS_NULL(vars)) {
+			if(symbol == HEAD(vars))
+				return HEAD(vals);
+
+			vars = TAIL(vars);
+			vals = TAIL(vals);
+		}
+
+		env = PARENT_FRAMES(env);
+	}
+
+	failure("Unbound variable found for symbol %s", symbol->symbol_value);
+}
+
+
+struct value*
+env_set(struct value* env, struct value* var, struct value* val)
+{
+	struct value *frame, *vars, *vals;
+
+	while(!IS_NULL(env)) {
+		frame = FIRST_FRAME(env);
+		vars = FRAME_VARIABLES(frame);
+		vals = FRAME_VALUES(frame);
+
+		while(!IS_NULL(vars)) {
+			if(var == HEAD(vars))
+				HEAD(vals) = val;
+				return True;
+
+			vars = TAIL(vars);
+			vals = TAIL(vals);
+		}
+
+		env = PARENT_FRAMES(env);
+	}
+
+	failure("Unbound variable found for symbol %s", var->symbol_value);
+}
+
+	
+struct value*
+env_add_binding_to_frame(struct value* frame, struct value* var, struct value* val)
+{
+	HEAD(frame) = cons(var, HEAD(frame));
+	TAIL(frame) = cons(val, TAIL(frame));
+}
+
+
+struct value*
+env_define(struct value* env, struct value* var, struct value* val)
+{
+	struct value* frame = FIRST_FRAME(env);
+	struct value* vars = FRAME_VARIABLES(frame);
+	struct value* vals = FRAME_VALUES(frame);
+
+	while(!IS_NULL(vars)) {
+		if(var == HEAD(vars)) {
+			HEAD(vals) = val;
+			return True;
+		}
+
+		vars = TAIL(vars);
+		vals = TAIL(vals);
+	}
+
+	env_add_binding_to_frame(var, val, frame);
+	return True;
+}
 
 
 

source/bootstrap.h

@@ -121,12 +121,22 @@ struct value*   cons(struct value* head, struct value* tail);
 #define list3(A, B, C) cons(A, cons(B, cons(C, emptylist)))
 #define list4(A, B, C, D) cons(A, cons(B, cons(C, cons(D, emptylist))))
 
-#define SYMBOL_ENTRY(sym, left, right) \
-	cons(sym, cons(left, right))
-
+#define SYMBOL_ENTRY(sym, left, right) cons(sym, cons(left, right))
 #define SYMBOL_LEFT(node) HEAD(TAIL(node))
 #define SYMBOL_RIGHT(node) TAIL(TAIL(node))
 
+#define EXTEND_ENV(env, vars, vals) cons(cons(vars,vals), env)
+#define INTIAL_ENV EXTEND_ENV(Emptylist, Emptylist, Emptylist)
+#define FIRST_FRAME(env) HEAD(env)
+#define PARENT_FRAMES(env) TAIL(env)
+#define FRAME_VARIABLES(frame) HEAD(frame)
+#define FRAME_VALUES(frame) TAIL(frame)
+
+struct value*	env_lookup(struct value* env, struct value* var);
+struct value*	env_set(struct value* env, struct value* var, struct value* val);
+struct value*	env_define(struct value* env, struct value* var, struct value* val);
+struct value*  	env_add_binding_to_frame(struct value* frame, struct value* var, struct value* val);
+
 
 struct closure {
     struct value* (*execute)(struct closure* self);