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render(
  <Provider store={store}>
    <Counter />
  </Provider>
  , document.getElementById('root'));

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const mapStateToProps = (state) => {
  return {counter: state.counter};
}
const mapDispatchToProps = (dispatch) => {
  return {
    onIncrement: () => dispatch({type: 'INCREMENT'}),
    onDecrement: () => dispatch({type: 'DECREMENT'})
  }
}
Counter = connect(mapStateToProps, mapDispatchToProps)(Counter);

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const store = createStore(reducer, {counter: 0},window.devToolsExtension ? window.devToolsExtension() : undefined);

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let Counter = ({counter, onIncrement, onDecrement}) =>
 (<div>
    <div>{counter}</div>
    <button onClick={onDecrement}>-</button>
    <button onClick={onIncrement}>+</button>
  </div>);

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const reducer = (state = {counter: 0}, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return {...state, counter: state.counter+1};
    case 'DECREMENT':
      return {...state, counter: state.counter-1};
    default:
      return state;
  }
};

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import React from 'react';
import { render } from 'react-dom';
import { createStore } from 'redux';
import { connect, Provider } from 'react-redux';

const reducer = (state = {counter: 0}, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return {...state, counter: state.counter+1};
    case 'DECREMENT':

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function pureFunction(a) {
  return a * 2;
}

var c = 6;
function impureFunction(a) {
  return c * a;
}

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scala> (-1000.0 to 1000.0 by 0.1).forall(x => df(x) == 8 * x + 6)
res0: Boolean = true

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f(x) = 4 * Math.pow(x, 2) + 6 * x - 5

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scala> val df = Scalac.derivative(x => 2*(2 * Math.pow(x, 2) + 3 * x) + (-5))
df: Double => Double = <function1>