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+/**
+ * Meta
+ */
+
+print = console.log
+y = f => x => f(y(f))(x)
+k = t => f => t
+ki = t => f => f
+
+/**
+ * Logic
+ */
+
+// true/false Church booleans
+tru = t => f => t
+fls = t => f => f
+
+// evaluate 
+evalBool = bool => bool("true")("false")
+
+print(evalBool(tru)) // "true"
+print(evalBool(fls)) // "false"
+
+// negate (c combinator)
+negate = bool => t => f => bool(f)(t)
+
+print(evalBool(negate(tru))) // "false"
+print(evalBool(negate(fls))) // "true"
+
+// logical and
+and = a => b => b(a)(b)
+
+// how?
+// - if b is true, then b is re-bound to a (first arg, see lines 1,3)
+// - if b is false, then b is re-bound to b (second arg, always false, see lines 2,4)
+
+print(evalBool(and(tru)(tru))) // "true"
+print(evalBool(and(tru)(fls))) // "false"
+print(evalBool(and(fls)(tru))) // "false"
+print(evalBool(and(fls)(fls))) // "false"
+
+/**
+ * Church Pairs
+ */
+
+// construction
+cons = a => b => s => s(a)(b)
+
+// example
+examplePair = cons("a")("b")
+
+// selectors
+car = pair => pair(a => b => a)
+cdr = pair => pair(a => b => b)
+
+print(car(examplePair)) // "a"
+print(cdr(examplePair)) // "b"
+
+/**
+ * Church Lists
+ */
+
+// ["a", "b", "c"] => pair "a" (pair "b" (pair "c" nil))
+//                 => s1 => (s1 "a" (s2 => (s2 "b" (s3 => (s3 "c" nil)))))
+
+// end of list
+nil = head => tail => tail
+
+exampleList = cons("a")(cons("b")(cons("c")(nil)))
+
+// true if list is empty
+isNil = list => list(head => tail => rest => fls)(tru)
+// first argument gets substituted into first selector (s1)
+//   just ignore all arguments and return false
+//   "rest" is the right argument "tru"
+// nil ignores first argument, second one is just returned as is ("true")
+
+print(evalBool(isNil(nil))) // "true"
+print(evalBool(isNil(exampleList))) // "false"
+
+// length = y(rec => n => list => isNil(list)(n)(rec(n + 1)(cdr(list))))(0)
+
+// thunked due to JS' strictness..
+length = y(rec => n => list => isNil(list)(() => n)(() => rec(n + 1)(cdr(list))()))(0)
+
+print(length(exampleList)())
+
+/**
+ * Scott Lists
+ */
+
+exampleScottList = end => s1 => s2("a")(s2 => s2("b")(end))
+
+/**
+ * Parigot Lists
+ */
+
+exampleParigotList = s1 => end1 => s1("a")(s2 => end2 => s2("b")(s3 => end3 => end3))
+
+/**
+ * Product types
+ */
+
+// data Friends = Friends { best :: String, friendly :: String, weird :: String }
+Friends = best => friendly => weird => s => s(best)(friendly)(weird)
+best = friends => friends(best => _ => _ => best)
+friendly = friends => friends(_ => friendly => _ => friendly)
+weird = friends => friends(_ => _ => weird => weird)
+
+friends = Friends("Alice")("Bob")("Carol")
+print(best(friends))
+
+/**
+ * Sum types, tagged unions
+ */
+
+// data Tree = Leaf Int | Node Tree Tree
+Leaf = n => leaf => node => leaf(n)
+Node = a => b => leaf => node => node(a)(b)
+nodeLeft = node => node(_ => _)(a => b => a)
+nodeRight = node => node(_ => _)(a => b => b)
+leafValue = leaf => leaf(n => n)(_ => _)
+isLeaf = tree => tree(n => tru)(a => b => fls)
+isNode = tree => tree(n => fls)(a => b => tru)
+
+exampleTree = Node(Leaf(1))(Node(Leaf(2))(Leaf(3)))
+print(evalBool(isNode(exampleTree)))
+print(evalBool(isLeaf(nodeLeft(exampleTree))))
+print(leafValue(nodeLeft(exampleTree)))
+print(leafValue(nodeRight(nodeRight(exampleTree))))
+
+/**
+ * Rose, Balanced, binary, finger, etc. trees
+ */
+
+// skipped, see bruijn std
+// for example: AVL - can even be used for sets and hashmaps!
+
+/**
+ * Strings, chars
+ */
+
+// just a list of numbers/bits/etc.
+
+/**
+ * Church numerals
+ */
+
+churchZero = s => z => z
+churchSucc = n => s => z => s(n(s)(z))
+churchPred = n => f => x => n(g => h => h(g(f)))(u => x)(u => u)
+churchIsZero = n => n(z => fls)(tru)
+
+print(evalBool(churchIsZero(churchZero))) // true
+print(evalBool(churchIsZero(churchSucc(churchZero)))) // false
+print(evalBool(churchIsZero(churchPred(churchSucc(churchZero))))) // true
+
+/**
+ * Scott numerals
+ */
+
+scottZero = z => s => z
+scottSucc = n => z => s => s(n)
+scottPred = n => n(scottZero)(x => x)
+scottIsZero = n => n(tru)(x => fls)
+
+print(evalBool(scottIsZero(scottZero))) // true
+print(evalBool(scottIsZero(scottSucc(scottZero)))) // false
+print(evalBool(scottIsZero(scottPred(scottSucc(scottZero))))) // true
+
+/**
+ * Parigot numerals
+ */
+
+parigotZero = n => n
+parigotSucc = n => a => b => b(n(a))
+parigotPred = n => a => n(a(x => x))
+
+/**
+ * Wadsworth numerals
+ */
+
+wadsworthZero = n => n(u => k)
+wadsworthSucc = n => a => b => n(c => a(b(c))(b))
+wadsworthPred = n => a => n(b => k(a(b)))(x => x)
+wadsworthIsZero = n => n(x => x)(k(k(ki)))
+
+print(evalBool(wadsworthIsZero(wadsworthZero))) // true
+print(evalBool(wadsworthIsZero(wadsworthSucc(wadsworthZero)))) // false
+print(evalBool(wadsworthIsZero(wadsworthPred(wadsworthSucc(wadsworthZero))))) // true
+
+/**
+ * de Bruijn numerals
+ */
+
+bruijnZero = n => n
+bruijnSucc = n => a => b => n(a)
+bruijnPred = n => a => n(a)(a)
+bruijnMult = a => b => a(b)
+
+/**
+ * n-ary numerals
+ */
+
+exampleMogensenBinary = end => b1 => b0 => b1(b1(end))
+exampleMogensenTernary = end => tn => tp => t0 => t0(tp(end))
+
+/**
+ * rational, real, complex
+ */
+
+// skipped, see bruijn std
+
+/**
+ * Maybe monad
+ */
+
+Nothing = empty => full => empty
+Just = v => empty => full => full(v)
+isNothing = m => m(tru)(u => fls)
+isJust = m => m(fls)(u => tru)
+map => f => m => m(nothing)(v => just(f(v)))
+
+pure = Just
+bind = mx => f => mx(mx)(f)
+//       ------------^^  ^-----------------
+//       case Nothing     case Just (apply)
+
+evalMaybe = maybe => maybe("Nothing")(v => "Just " + v)
+print(evalMaybe(bind(Nothing)(n => pure(n + 1))))
+print(evalMaybe(bind(Just(42))(n => pure(n + 1))))
+
+/**
+ * Either monad
+ */
+
+// data Either a b = Left a | Right b
+Left = a => left => right => left(a)
+Right = b => left => right => right(b)
+
+// instance Monad
+pure = Right
+bind = mx => f => mx(Left)(f)
+//          ---------^^^^  ^------------------
+//          case Left       case Right (apply)
+
+evalEither = either => either(a => "Left " + a)(b => "Right " + b)
+print(evalEither(bind(Left(42))(n => pure(n + 1))))
+print(evalEither(bind(Right(42))(n => pure(n + 1))))
+
+/**
+ * Mogensen-Scott meta
+ */
+
+// enc[x]      = sym => app => lam => sym(x)
+// enc[f(x)]   = sym => app => lam => app(enc[f])(enc[x])
+// enc[x => m] = sym => app => lam => lam(x => enc[m])
+
+evalMeta = term => term
+  (x => x)
+  (f => x => eval(f)(eval(x)))
+  (m => x => eval(m(x)))
+
+/**
+ * Bruijn-Church meta
+ */
+
+// enc[i]    = idx => app => lam => church[idx]
+// enc[f(x)] = idx => app => lam => app(enc[f])(enc[x])
+// enc[b]    = idx => app => lam => lam(enc[b])
+
+/**
+ * Lambda Screen
+ */
+
+// a screen is (s => s(tl)(tr)(bl)(br)), where tl,tr,bl,br in [screen, pixel]
+//   pixel is (w => b => w) || (w => b => b)