Lambda calculus in js form

lambda.js

const Identity = a => a
const True = a => b => a
const False = b => Identity
const Condition = Predicate => Then => Else => Predicate(Then)(Else)
const And = Exp1 => Exp2 => Exp1(Exp2)(Exp1)
const Or = Exp1 => Exp2 => Exp1(Exp1)(Exp2)
const Not = Predicate => value => !Predicate(value)
const Defined = x => typeof x !== 'undefined'
// aliases
const T = True
const F = False
const If = Condition
// Arrays
const Head = ([ first ]) => first
const Tail = ([, ...items ]) => items
const Reduce = fn => ([ item, ...rest ], memo = []) => Defined(item)
  ? Reduce(fn)(rest, fn(memo, item)) 
  : memo
const Each = fn => Reduce(( arr, item ) => [ ...arr, fn(item) ])
const Filter = fn => Reduce(( arr, item ) => fn(item) ? [ ...arr, item ] : arr )

const λ =
  { Identity
  , True
  , T
  , False
  , F
  , Condition
  , If
  , And
  , Or
  , Not
  , Defined
  , Head
  , Tail
  , Reduce
  , Each
  , Filter
  }

module.exports = λ

// For testing:

const log = (...things) => console.log(...things)
const pipe = (...fns) => val => fns.reduce((val,fn)=>fn(val),val)

const isTrue = pipe(() => 'true!', log)
const isFalse = pipe(() => 'false!', log)


const Result1 = If(And(True)(True))(isTrue)(isFalse)

const Result2 = If(And(True)(False))(isTrue)(isFalse)

const Result3 = If(Or(False)(True))(isTrue)(isFalse)

const Result4 = If(Or(False)(False))(isTrue)(isFalse)

Result1() // "true!"
Result2() // "false!"
Result3() // "true!"
Result4() // "false!"