Question

我正在使用TatSu python库实现语法。我的语法工作正常，但是有一条规则要花很多时间。在大约3000行的块（较大语法的一部分）上，如果我遵循这条完整规则，则解析整个块大约需要42秒。如果我将此规则简化为几个标记，则运行时间将从42s降至33s（提高了20％）。

规则如下所示，它应与一系列事件相匹配，并用'/'分隔。

import { createStore, applyMiddleware, compose } from 'redux';
import { routerMiddleware } from 'connected-react-router';
import { fromJS } from 'immutable';
import createSagaMiddleware from 'redux-saga';
import createReducer from './reducers'
import sagas from './utils/sagas';
import * as storage from 'redux-storage';
import createEngine from 'redux-storage-engine-localstorage';

const sagaMiddleware = createSagaMiddleware();

export default function configureStore(initialState={}, history){
  const engine = createEngine('my-save-key');
    const middleware = storage.createMiddleware(engine);
    const middlewares = [middleware,sagaMiddleware, routerMiddleware(history)];

    const enhancers = [applyMiddleware(...middlewares)];

    const composeEnhancers = process.env.NODE_ENV !== 'production'
    && typeof window === 'object'
    && window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__
      ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__({
          // Prevent recomputing reducers for `replaceReducer`
          shouldHotReload: false,
        })
      : compose;
  /* eslint-enable */
  const store = createStore(
    createReducer(),
    fromJS(initialState),
    composeEnhancers(...enhancers),
  );

  // Extensions
  sagaMiddleware.run(sagas);
  store.injectedReducers = {}; // Reducer registry
  store.injectedSagas = {}; // Saga registry


  // Make reducers hot reloadable, see http://mxs.is/googmo
  /* istanbul ignore next */
  if (module.hot) {
    module.hot.accept('./reducers', () => {
      store.replaceReducer(createReducer(store.injectedReducers));
    });
  }
  const load = storage.createLoader(engine);
  load(store)
  .then((newState) => console.log('Loaded state:', newState))
  .catch((err) => console.log('Failed to load previous state', err));

  return store;
}

如果将 event 更改为以下内容，则可以更快地进行解析。

import { reducer as form } from 'redux-form/immutable';
import { combineReducers } from 'redux';
import { connectRouter } from 'connected-react-router';
import history from './utils/history';
import * as storage from 'redux-storage';

//Global Reducers
import authReducer from './modules/reducers/authReducer';

export default function createReducer(injectedReducers={}){
    const rootReducer = storage.reducer(combineReducers({

        authReducer,
        router: connectRouter(history),
        ...injectedReducers
    }))
 const mergeWithRouterState = connectRouter(history);
  return mergeWithRouterState(rootReducer);
}

那么可以通过某种方式改进上述规则以获得更快的处理速度吗？谢谢你的想法。

Answer 1

正如您所指出的，对于具有很多仅作为标记的选项的规则，使用模式（正则表达式）会更加有效。

但是运行时最终取决于某些规则如何相互调用。

您可以尝试的一种简单优化方法是添加一个cut（˜）表达式，这样每个event最多可以尝试一次（尽管 cut 应该在%表达式）。

event
    =
    (
    'D' | 'U' | 'Z' | 'P' | 'L' | 'H' | 'x' | 'X' | 'T' | 'V' | 'l' | 'h' | 't' | 'v' | 'N' | 'A' | 'B' | 'F' | '?' | 'G' | 'R' | 'Q' | 'M'
    | 'ForceDown' | 'ForceUp' | 'ForceOff' | 'ForcePrior' | 'CompareLow' | 'CompareHigh' | 'CompareUnknown' | 'CompareOff'
    | 'CompareValid' | 'CompareLowWindow' | 'CompareHighWindow' | 'CompareOffWindow' | 'CompareValidWindow' | 'ForceUnknown'
    | 'LogicLow' | 'LogicHigh' | 'LogicZ' | 'Unknown' | 'ExpectHigh' | 'ExpectLow' | 'ExpectOff' | 'Marker'
    ) ~
    ;

这就是说，因为该规则是 lexical 类的大部分，所以我选择正则表达式。

event
    =
    /(?x)
    'D' | 'U' | 'Z' | 'P' | 'L' | 'H' | 'x' | 'X' | 'T' | 'V' | 'l' | 'h' | 't' | 'v' | 'N' | 'A' | 'B' | 'F' | '?' | 'G' | 'R' | 'Q' | 'M'
    | 'ForceDown' | 'ForceUp' | 'ForceOff' | 'ForcePrior' | 'CompareLow' | 'CompareHigh' | 'CompareUnknown' | 'CompareOff'
    | 'CompareValid' | 'CompareLowWindow' | 'CompareHighWindow' | 'CompareOffWindow' | 'CompareValidWindow' | 'ForceUnknown'
    | 'LogicLow' | 'LogicHigh' | 'LogicZ' | 'Unknown' | 'ExpectHigh' | 'ExpectLow' | 'ExpectOff' | 'Marker'
    /
    ;

如何优化此语法规则？

1 个答案: