reduce.ts

const arr = <any>[1,2,3];

// why does typescript think sum is `any` instead of `num`? shouldn't it use the type of
// initialValue here?
const arrSum = arr.reduce((acc, val) => acc + val, 0);    // arrSum is `any`

// ImmutableJS does this correctly:
import I from 'immutable';
const list = I.List<any>().push(1).push(2).push(3);
const listSum = list.reduce((acc, val) => acc + val, 0);  // listSum is `number`

looks like this is the culprit: microsoft/TypeScript#7014