Currying a flipped function using lodash - Are there limitations?

Question

I'm new to lodash and just playing around with it to become familiar. I'm trying to curry a flipped function and I'm getting a TypeError.

Currying the same 'unflipped' function works as expected.

const curriedMap = _.curry(_.map);
const squares1 = curriedMap([ 1, 2, 3, 4 ]);

console.log(squares1(x => x * x)); // [ 1, 4, 9, 16 ]


const flippedMap = _.flip(_.map);

console.log(flippedMap(x => x * x, [1, 2, 3, 4])); // [ 1, 4, 9, 16 ]

const curriedFlippedMap = _.curry(flippedMap);

const makeSquares = curriedFlippedMap(x => x * x);

console.log(makeSquares([1, 2, 3, 4])); // TypeError: makeSquares is not a function

I'm expecting the last line to produce [ 1, 4, 9, 16 ] , but instead I get 'TypeError'. What am I doing wrong?

Answer 1

_.map has a length property (number of parameters) that _.curry can use to curry it automatically, but _.flip(_.map) can't easily produce a new function with the same length as its input (it reverses the entire argument list, it's not just f => (a, b) => f(b, a) ).

> _.map.length
2

> _.flip(_.map).length
0

_.curry lets you specify the number of parameters to work around that:

const curriedFlippedMap = _.curry(flippedMap, 2);