import { fieldNumber } from 'fp-ts/lib/Field' ; import { Endomorphism } from 'fp-ts/lib/function' ; since export function add ( x ) ; export function add ( x , y ) ; export function add ( x , y ? ) { if ( y === undefined ) { return y => fieldNumber . add ( x , y ) ; } else { return fieldNumber . add ( x , y ) ; } }