Add parser state code and skeleton for the parsing procedure.

src/parser.c

@@ -0,0 +1,29 @@
+struct parser_state {
+    ll_node* current_node;
+    lexer_match* current_match;
+    const char* string;
+};
+
+void _parser_state_update(struct parser_state* state) {
+    state->current_match = state->current_node ? state->current_node->data : NULL;
+}
+
+void _parser_state_init(struct parser_state* state, ll* tokens, const char* string) {
+    state->current_node = tokens->head;
+    state->string = string;
+    _parser_state_update(state);
+}
+
+void _parser_state_step(struct parser_state* state) {
+    if(state->current_node) {
+        state->current_node = state->current_node->next;
+    }
+    _parser_state_update(state);
+}
+libab_result parse_tokens(ll* tokens, const char* string, tree** store_into) {
+    libab_result result = LIBAB_SUCCESS;
+    struct parser_state state;
+    _parser_state_init(&state, tokens, string);
+
+    return result;
+}