Type argument for type parameter 'TResult' cannot be inferred

[HomenSimpsor]

Hey @donnut, thanks for doing these definitions. I have a question that might have a simple answer. I can't figure out how to make a legal use of R.reduce:

/// <reference path="typings/ramda/ramda.d.ts"/>

import R = require('ramda');

var add = (item: number, sum: number): number => sum + item

var avg = (list: Array<number>): any => {
  var sum: number = R.reduce(add, list);
  return sum / list.length;
}

error TS2453: The type argument for type parameter 'TResult' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
  Type argument candidate 'number' is not a valid type argument because it is not a supertype of candidate 'number[]'.

[donnut]

Hi @Wideshanks

reduce expects another argument, the initial value of the accumulator sum. If you specify:

var sum: number = R.reduce(add, 0, list);

it will probably work.

BTW, Typescript can infere the return types of add, any and the call to reduce, so you could simplify the code to:

    var add = (item: number, sum: number) => sum + item

    var avg = (list: Array<number>) => {
        var sum = R.reduce(add, 0, list);
        return sum / list.length;
    }

[HomenSimpsor]

Ah, thanks!