sum-type/lib/functor.js

A simple library for complex logic

import 
	{ assertValidVisitor
	, otherwise
	, mapAll
	} 
from './core.js'

export const trait = tag => T => {
	T.traits['sum-type/functor'] = tag

	T.of = T[tag]
	T.map =
		T.map
		|| (f => {
			assertValidVisitor({ context: 'map', visitor: f })
			return mapAll(T)({
				...otherwise(T.tags)(x => x)
				,[tag]: f,
			})
		})

	return T
}