Implement set!

src/built_ins.cpp

@@ -445,6 +445,28 @@ proc load_built_ins_into_environment() -> void {
             *target = *source;
             return target;
         });
+    defun("set!", "TODO", __LINE__, cLambda {
+            try assert_arguments_length(2, list_length(arguments));
+            Lisp_Object* target_symbol = arguments->value.pair.first;
+            try assert(target_symbol);
+            try assert(arguments->value.pair.rest->value.pair.first);
+            Lisp_Object* source = eval_expr(arguments->value.pair.rest->value.pair.first);
+
+            try assert(source);
+            try assert_type(target_symbol, Lisp_Object_Type::Symbol);
+
+            Environment* target_env = find_binding_environment(target_symbol->value.symbol.identifier, get_current_environment());
+            assert(target_env);
+
+            push_environment(target_env);
+            defer {
+                pop_environment();
+            };
+
+            define_symbol(target_symbol, source);
+
+            return source;
+        });
     defun("if", "TODO", __LINE__, cLambda {
             try arguments_length = list_length(arguments);
             try assert_arguments_length_greater_equal(2, arguments_length);

src/env.cpp

@@ -8,7 +8,7 @@ proc define_symbol(Lisp_Object* symbol, Lisp_Object* value) -> void {
 
     if (env->next_index == env->capacity) {
         env->capacity *= 2;
-        env->keys   =     (char**)realloc(env->keys,   env->capacity * sizeof(char*));
+        env->keys   =        (char**)realloc(env->keys,   env->capacity * sizeof(char*));
         env->values = (Lisp_Object**)realloc(env->values, env->capacity * sizeof(Lisp_Object*));
     }
 
@@ -24,6 +24,20 @@ proc lookup_symbol_in_this_envt(String* identifier, Environment* env) -> Lisp_Ob
     return nullptr;
 }
 
+proc environment_binds_symbol(String* identifier, Environment* env) -> bool {
+    return lookup_symbol_in_this_envt(identifier, env) != nullptr;
+}
+
+proc find_binding_environment(String* identifier, Environment* env) -> Environment* {
+    if (environment_binds_symbol(identifier, env))
+        return env;
+    for (int i = 0; i < env->parents->next_index; ++i) {
+        if (environment_binds_symbol(identifier, env->parents->data[i]))
+            return env->parents->data[i];
+    }
+    return get_root_environment();
+}
+
 proc try_lookup_symbol(Lisp_Object* node, Environment* env) -> Lisp_Object* {
     // first check current environment
     String* identifier = node->value.symbol.identifier;

src/structs.cpp

@@ -17,8 +17,8 @@ enum struct Lisp_Object_Type {
     String,
     Pair,
     Continuation,
-    Pointer,
-    OwningPointer,
+    // Pointer,
+    // OwningPointer,
     Function,
     CFunction,
 };