diff --git a/src/bf.ts b/src/bf.ts
new file mode 100644
index 0000000..8895c41
--- /dev/null
+++ b/src/bf.ts
@@ -0,0 +1,85 @@
+import { L, _, fromNative as __ } from './core';
+import { Bool, iif } from './bool';
+import { Num, Zero, ge, ifz, pred, succ } from './num';
+import { x00 } from './byte';
+import { Char, fromChar as _c, dec as cdec, inc as cinc, eq, ifn } from './char';
+import { Pair, first, fst, second, snd, uncurry } from './pair';
+import { List, Nil, cons, head, repeat, set, tail, update } from './list';
+import { Empty, String, get, len, snoc } from './string';
+
+type Program = Pair<List<Num>, String>;
+
+type Tape = Pair<Num, List<Char>>;
+
+type IO = Pair<String, String>;
+
+type State = Pair<Program, Pair<Tape, IO>>;
+
+const pcommand: L<(p: Program) => Char>
+  = uncurry._(_(is => get._(head._(is))));
+
+const padvance: L<(p: Program) => Program>
+  = first._(update._(succ)._(Zero));
+
+const pjump: L<(d: Num) => L<(p: Program) => Program>>
+  = _(d => _(p =>
+    iif._<Program>(eq._(_c('['))._(pcommand._(p)))._(pjump._(succ._(d))._(padvance._(p)))
+      ._(iif._<Program>(eq._(_c(']'))._(pcommand._(p)))._(ifz._<Program>(pred._(d))._(p)._(pjump._(pred._(d))._(padvance._(p))))
+        ._(pjump._(d)._(padvance._(p))))));
+
+const done: L<(s: State) => Bool>
+  = _(s => uncurry._(_(is => _(cs => ge._(head._(is))._(len._(cs)))))._(fst._(s)));
+
+const command: L<(s: State) => Char>
+  = _(s => pcommand._(fst._(s)));
+
+const advance: L<(s: State) => State>
+  = first._(padvance);
+
+const jump: L<(s: State) => State>
+  = first._(pjump._(Zero));
+
+const save: L<(s: State) => State>
+  = first._(first._(_(is => cons._(head._(is))._(is))));
+
+const restore: L<(s: State) => State>
+  = first._(first._(tail));
+
+const reset: L<(s: State) => State>
+  = first._(first._(_(is => cons._(head._(is))._(tail._(tail._(is))))));
+
+const inc: L<(t: State) => State>
+  = second._(first._(_(t => second._(update._(cinc)._(fst._(t)))._(t))));
+
+const dec: L<(t: State) => State>
+  = second._(first._(_(t => second._(update._(cdec)._(fst._(t)))._(t))));
+
+const read: L<(s: State) => Char>
+  = _(s => uncurry._(get)._(fst._(snd._(s))));
+
+const input: L<(s: State) => State>
+  = second._(uncurry._(_(t => _(io => Pair._(second._(set._(head._(fst._(io)))._(fst._(t)))._(t))._(first._(tail)._(io))))));
+
+const output: L<(s: State) => State>
+  = second._(uncurry._(_(t => _(io => Pair._(t)._(second._(_(os => snoc._(os)._(uncurry._(get)._(t))))._(io))))));
+
+const next: L<(t: State) => State>
+  = second._(first._(first._(succ)));
+
+const prev: L<(t: State) => State>
+  = second._(first._(first._(pred)));
+
+const exec: L<(s: State) => State>
+  = _(s => iif._<State>(done._(s))._(s)._(exec._(advance
+    ._(iif._<State>(eq._(_c('>'))._(command._(s)))._(next._(s))
+      ._(iif._<State>(eq._(_c('<'))._(command._(s)))._(prev._(s))
+        ._(iif._<State>(eq._(_c('+'))._(command._(s)))._(inc._(s))
+          ._(iif._<State>(eq._(_c('-'))._(command._(s)))._(dec._(s))
+            ._(iif._<State>(eq._(_c('.'))._(command._(s)))._(output._(s))
+              ._(iif._<State>(eq._(_c(','))._(command._(s)))._(input._(s))
+                ._(iif._<State>(eq._(_c('['))._(command._(s)))._(ifn._<State>(read._(s))._(jump._(s))._(save._(s)))
+                  ._(iif._<State>(eq._(_c(']'))._(command._(s)))._(ifn._<State>(read._(s))._(reset._(s))._(save._(restore._(s))))
+                    ._(s))))))))))));
+
+export const run: L<(p: String) => L<(i: String) => String>>
+  = _(p => _(i => snd._(snd._(snd._(exec._(Pair._(Pair._(cons._(Zero)._(Nil))._(p))._(Pair._(Pair._(Zero)._(repeat._(x00)))._(Pair._(i)._(Empty)))))))));
diff --git a/src/byte.ts b/src/byte.ts
new file mode 100644
index 0000000..fbcebc9
--- /dev/null
+++ b/src/byte.ts
@@ -0,0 +1,34 @@
+import { L, _, id } from './core';
+import { iif } from './bool';
+import { Num, Succ, Zero, fromNumber as _n, eq } from './num';
+
+export type Byte = Num;
+
+export const x00: Byte
+  = Zero;
+
+export const xFF: Num
+  = _n(255);
+
+export const Inc: L<(p: Byte) => Byte>
+  = _(p => iif._(eq._(xFF)._(p))._(x00)._(Succ._(p)));
+
+export { ifz, cmp, lt, le, eq, ge, gt, even, odd, div, mod, show, toNumber } from './num';
+
+export const inc: L<(n: Byte) => Byte>
+  = Inc;
+
+export const dec: L<(n: Byte) => Byte>
+  = _(n => n._(xFF)._(id));
+
+export const sum: L<(l: Byte) => L<(r: Byte) => Byte>>
+  = _(l => _(r => r._(l)._(_(pr => sum._(inc._(l))._(pr)))));
+
+export const sub: L<(l: Byte) => L<(r: Byte) => Byte>>
+  = _(l => _(r => r._(l)._(_(pr => sub._(dec._(l))._(pr)))));
+
+export const mul: L<(l: Byte) => L<(r: Byte) => Byte>>
+  = _(l => _(r => l._(x00)._(_(pl => sum._(r)._(mul._(pl)._(r))))));
+
+export const fromNumber: (n: number) => Byte
+  = n => _n(n % 256);
diff --git a/src/index.ts b/src/index.ts
index e4c7cd7..59543ed 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,8 @@
 export * from './core';
 export * from './bool';
 export * from './num';
-export * from './list';
+export * from './byte';
 export * from './char';
+export * from './list';
 export * from './pair';
+export * from './bf';
diff --git a/src/list.ts b/src/list.ts
index c86f3c0..8e67651 100644
--- a/src/list.ts
+++ b/src/list.ts
@@ -31,6 +31,9 @@ export const append: L<<T extends P>(l: List<T>) => L<(r: List<T>) => List<T>>>
 export const concat: L<<T extends P>(ls: List<List<T>>) => List<T>>
   = _(ls => ls._(Nil)._(_(x => _(xs => append._(x)._(concat._(xs))))));
 
+export const repeat: L<<T extends P>(v: T) => List<T>>
+  = _(v => cons._(v)._(repeat._(v)));
+
 export const head: L<<T extends P>(xs: List<T>) => T>
   = _(xs => xs._(undef)._(_(x => _(_xs => x))));
 
diff --git a/test/bf.spec.ts b/test/bf.spec.ts
new file mode 100644
index 0000000..ae77ce8
--- /dev/null
+++ b/test/bf.spec.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it } from '@jest/globals';
+import { _ } from '../src/core';
+import { fromChar as _c } from '../src/char';
+import { toString as $s, fromString as _s } from '../src/string';
+import { run } from '../src/bf';
+
+describe('BF', () => {
+  describe('run', () => {
+    it('handles output command', () => {
+      expect($s(run._(_s('.'))._(_s('')))).toBe(String.fromCharCode(0));
+    });
+
+    it('handles input command', () => {
+      expect($s(run._(_s(',.'))._(_s('a')))).toBe('a');
+    });
+
+    it('handles inc command', () => {
+      expect($s(run._(_s('+.'))._(_s('')))).toBe(String.fromCharCode(1));
+    });
+
+    it('handles dec command', () => {
+      expect($s(run._(_s('-.'))._(_s('')))).toBe(String.fromCharCode(255));
+    });
+
+    it('handles next command', () => {
+      expect($s(run._(_s('+++++>++.'))._(_s('')))).toBe(String.fromCharCode(2));
+    });
+
+    it('handles prev command', () => {
+      expect($s(run._(_s('+++++>++<+++++.'))._(_s('')))).toBe(String.fromCharCode(10));
+    });
+
+    it('skips loop block on zero', () => {
+      expect($s(run._(_s('[+++++].'))._(_s('')))).toBe(String.fromCharCode(0));
+    });
+
+    it('repeats loop block while not zero', () => {
+      expect($s(run._(_s('+++++[-].'))._(_s('')))).toBe(String.fromCharCode(0));
+    });
+
+    it('prints "Hello World!"', () => {
+      expect($s(run
+        ._(_s('++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.'))
+        ._(_s(''))))
+        .toBe('Hello World!\n');
+    });
+  });
+});
diff --git a/test/byte.spec.ts b/test/byte.spec.ts
new file mode 100644
index 0000000..cf74475
--- /dev/null
+++ b/test/byte.spec.ts
@@ -0,0 +1,475 @@
+import { describe, expect, it } from '@jest/globals';
+import { undef } from '../src/core';
+import { toNOrd as $o, NOrd } from '../src/ord';
+import { toBoolean as $b, fromBoolean as _b } from '../src/bool';
+import { toNumber as $n, Inc, fromNumber as _n, cmp, dec, div, eq, ge, gt, ifz, inc, le, lt, mod, mul, show, sub, sum, x00 } from '../src/byte';
+import { toString as $s } from '../src/string';
+
+describe('Byte', () => {
+  describe('toNumber', () => {
+    it('converts 0', () => {
+      expect($n(x00)).toBe(0);
+    });
+
+    it('converts 1', () => {
+      expect($n(Inc._(x00))).toBe(1);
+    });
+
+    it('converts 2', () => {
+      expect($n(Inc._(Inc._(x00)))).toBe(2);
+    });
+  });
+
+  describe('fromNumber', () => {
+    it('converts 0', () => {
+      expect($n(_n(0))).toBe(0);
+    });
+
+    it('converts 1', () => {
+      expect($n(_n(1))).toBe(1);
+    });
+
+    it('converts 2', () => {
+      expect($n(_n(2))).toBe(2);
+    });
+
+    it('converts 300', () => {
+      expect($n(_n(300))).toBe(44);
+    });
+  });
+
+  describe('ifz', () => {
+    it('returns zero branch', () => {
+      expect($b(ifz._(_n(0))._(_b(true))._(_b(false)))).toBe(true);
+    });
+
+    it('returns non-zero branch', () => {
+      expect($b(ifz._(_n(1))._(_b(true))._(_b(false)))).toBe(false);
+    });
+
+    it('returns non-zero branch', () => {
+      expect($b(ifz._(_n(10))._(_b(true))._(_b(false)))).toBe(false);
+    });
+
+    it('skips other branch', () => {
+      expect($b(ifz._(_n(0))._(_b(true))._(undef))).toBe(true);
+      expect($b(ifz._(_n(1))._(undef)._(_b(false)))).toBe(false);
+    });
+  });
+
+  describe('inc', () => {
+    it('inc 0 is 1', () => {
+      expect($n(inc._(_n(0)))).toBe(1);
+    });
+
+    it('inc 1 is 2', () => {
+      expect($n(inc._(_n(1)))).toBe(2);
+    });
+
+    it('inc 10 is 11', () => {
+      expect($n(inc._(_n(10)))).toBe(11);
+    });
+
+    it('inc 255 is 0', () => {
+      expect($n(inc._(_n(255)))).toBe(0);
+    });
+  });
+
+  describe('dec', () => {
+    it('dec 0 is 255', () => {
+      expect($n(dec._(_n(0)))).toBe(255);
+    });
+
+    it('dec 1 is 0', () => {
+      expect($n(dec._(_n(1)))).toBe(0);
+    });
+
+    it('dec 10 is 9', () => {
+      expect($n(dec._(_n(10)))).toBe(9);
+    });
+
+    it('dec 255 is 254', () => {
+      expect($n(dec._(_n(255)))).toBe(254);
+    });
+  });
+
+  describe('cmp', () => {
+    it('0 cmp 0 is EQ', () => {
+      expect($o(cmp._(_n(0))._(_n(0)))).toBe(NOrd.EQ);
+    });
+
+    it('0 cmp 1 is LT', () => {
+      expect($o(cmp._(_n(0))._(_n(1)))).toBe(NOrd.LT);
+    });
+
+    it('1 cmp 0 is GT', () => {
+      expect($o(cmp._(_n(1))._(_n(0)))).toBe(NOrd.GT);
+    });
+
+    it('3 cmp 3 is EQ', () => {
+      expect($o(cmp._(_n(3))._(_n(3)))).toBe(NOrd.EQ);
+    });
+
+    it('3 cmp 7 is LT', () => {
+      expect($o(cmp._(_n(3))._(_n(7)))).toBe(NOrd.LT);
+    });
+
+    it('7 cmp 3 is GT', () => {
+      expect($o(cmp._(_n(7))._(_n(3)))).toBe(NOrd.GT);
+    });
+
+    it('0 cmp 255 is LT', () => {
+      expect($o(cmp._(_n(0))._(_n(255)))).toBe(NOrd.LT);
+    });
+
+    it('255 cmp 0 is GT', () => {
+      expect($o(cmp._(_n(255))._(_n(0)))).toBe(NOrd.GT);
+    });
+
+    it('255 cmp 255 is EQ', () => {
+      expect($o(cmp._(_n(255))._(_n(255)))).toBe(NOrd.EQ);
+    });
+  });
+
+  describe('lt', () => {
+    it('0 lt 0 is False', () => {
+      expect($b(lt._(_n(0))._(_n(0)))).toBe(false);
+    });
+
+    it('0 lt 1 is True', () => {
+      expect($b(lt._(_n(0))._(_n(1)))).toBe(true);
+    });
+
+    it('1 lt 0 is False', () => {
+      expect($b(lt._(_n(1))._(_n(0)))).toBe(false);
+    });
+
+    it('3 lt 3 is False', () => {
+      expect($b(lt._(_n(3))._(_n(3)))).toBe(false);
+    });
+
+    it('3 lt 7 is True', () => {
+      expect($b(lt._(_n(3))._(_n(7)))).toBe(true);
+    });
+
+    it('7 lt 3 is False', () => {
+      expect($b(lt._(_n(7))._(_n(3)))).toBe(false);
+    });
+
+    it('0 lt 255 is True', () => {
+      expect($b(lt._(_n(0))._(_n(255)))).toBe(true);
+    });
+
+    it('255 lt 0 is False', () => {
+      expect($b(lt._(_n(255))._(_n(0)))).toBe(false);
+    });
+
+    it('255 lt 255 is False', () => {
+      expect($b(lt._(_n(255))._(_n(255)))).toBe(false);
+    });
+  });
+
+  describe('le', () => {
+    it('0 le 0 is True', () => {
+      expect($b(le._(_n(0))._(_n(0)))).toBe(true);
+    });
+
+    it('0 le 1 is True', () => {
+      expect($b(le._(_n(0))._(_n(1)))).toBe(true);
+    });
+
+    it('1 le 0 is False', () => {
+      expect($b(le._(_n(1))._(_n(0)))).toBe(false);
+    });
+
+    it('3 le 3 is True', () => {
+      expect($b(le._(_n(3))._(_n(3)))).toBe(true);
+    });
+
+    it('3 le 7 is True', () => {
+      expect($b(le._(_n(3))._(_n(7)))).toBe(true);
+    });
+
+    it('7 le 3 is False', () => {
+      expect($b(le._(_n(7))._(_n(3)))).toBe(false);
+    });
+
+    it('0 le 255 is True', () => {
+      expect($b(le._(_n(0))._(_n(255)))).toBe(true);
+    });
+
+    it('255 le 0 is False', () => {
+      expect($b(le._(_n(255))._(_n(0)))).toBe(false);
+    });
+
+    it('255 le 255 is True', () => {
+      expect($b(le._(_n(255))._(_n(255)))).toBe(true);
+    });
+
+    it('0 le skips second argument', () => {
+      expect($b(le._(_n(0))._(undef))).toBe(true);
+    });
+  });
+
+  describe('eq', () => {
+    it('0 eq 0 is True', () => {
+      expect($b(eq._(_n(0))._(_n(0)))).toBe(true);
+    });
+
+    it('0 eq 1 is False', () => {
+      expect($b(eq._(_n(0))._(_n(1)))).toBe(false);
+    });
+
+    it('1 eq 0 is False', () => {
+      expect($b(eq._(_n(1))._(_n(0)))).toBe(false);
+    });
+
+    it('3 eq 3 is True', () => {
+      expect($b(eq._(_n(3))._(_n(3)))).toBe(true);
+    });
+
+    it('3 eq 7 is False', () => {
+      expect($b(eq._(_n(3))._(_n(7)))).toBe(false);
+    });
+
+    it('7 eq 3 is False', () => {
+      expect($b(eq._(_n(7))._(_n(3)))).toBe(false);
+    });
+
+    it('0 eq 255 is False', () => {
+      expect($b(eq._(_n(0))._(_n(255)))).toBe(false);
+    });
+
+    it('255 eq 0 is False', () => {
+      expect($b(eq._(_n(255))._(_n(0)))).toBe(false);
+    });
+
+    it('255 eq 255 is True', () => {
+      expect($b(eq._(_n(255))._(_n(255)))).toBe(true);
+    });
+  });
+
+  describe('ge', () => {
+    it('0 ge 0 is True', () => {
+      expect($b(ge._(_n(0))._(_n(0)))).toBe(true);
+    });
+
+    it('0 ge 1 is False', () => {
+      expect($b(ge._(_n(0))._(_n(1)))).toBe(false);
+    });
+
+    it('1 ge 0 is True', () => {
+      expect($b(ge._(_n(1))._(_n(0)))).toBe(true);
+    });
+
+    it('3 ge 3 is True', () => {
+      expect($b(ge._(_n(3))._(_n(3)))).toBe(true);
+    });
+
+    it('3 ge 7 is False', () => {
+      expect($b(ge._(_n(3))._(_n(7)))).toBe(false);
+    });
+
+    it('7 ge 3 is True', () => {
+      expect($b(ge._(_n(7))._(_n(3)))).toBe(true);
+    });
+
+    it('0 ge 255 is False', () => {
+      expect($b(ge._(_n(0))._(_n(255)))).toBe(false);
+    });
+
+    it('255 ge 0 is True', () => {
+      expect($b(ge._(_n(255))._(_n(0)))).toBe(true);
+    });
+
+    it('255 ge 255 is True', () => {
+      expect($b(ge._(_n(255))._(_n(255)))).toBe(true);
+    });
+
+    it('ge 0 skips first argument', () => {
+      expect($b(ge._(undef)._(_n(0)))).toBe(true);
+    });
+  });
+
+  describe('gt', () => {
+    it('0 gt 0 is False', () => {
+      expect($b(gt._(_n(0))._(_n(0)))).toBe(false);
+    });
+
+    it('0 gt 1 is False', () => {
+      expect($b(gt._(_n(0))._(_n(1)))).toBe(false);
+    });
+
+    it('1 gt 0 is True', () => {
+      expect($b(gt._(_n(1))._(_n(0)))).toBe(true);
+    });
+
+    it('3 gt 3 is False', () => {
+      expect($b(gt._(_n(3))._(_n(3)))).toBe(false);
+    });
+
+    it('3 gt 7 is False', () => {
+      expect($b(gt._(_n(3))._(_n(7)))).toBe(false);
+    });
+
+    it('7 gt 3 is True', () => {
+      expect($b(gt._(_n(7))._(_n(3)))).toBe(true);
+    });
+
+    it('0 gt 255 is False', () => {
+      expect($b(gt._(_n(0))._(_n(255)))).toBe(false);
+    });
+
+    it('255 gt 0 is True', () => {
+      expect($b(gt._(_n(255))._(_n(0)))).toBe(true);
+    });
+
+    it('255 gt 255 is False', () => {
+      expect($b(gt._(_n(255))._(_n(255)))).toBe(false);
+    });
+  });
+
+  describe('sum', () => {
+    it('0 sum 0 is 0', () => {
+      expect($n(sum._(_n(0))._(_n(0)))).toBe(0);
+    });
+
+    it('0 sum 1 is 1', () => {
+      expect($n(sum._(_n(0))._(_n(1)))).toBe(1);
+    });
+
+    it('1 sum 0 is 1', () => {
+      expect($n(sum._(_n(1))._(_n(0)))).toBe(1);
+    });
+
+    it('3 sum 4 is 7', () => {
+      expect($n(sum._(_n(3))._(_n(4)))).toBe(7);
+    });
+
+    it('200 sum 200 is 144', () => {
+      expect($n(sum._(_n(200))._(_n(200)))).toBe(144);
+    });
+  });
+
+  describe('sub', () => {
+    it('0 sub 0 is 0', () => {
+      expect($n(sub._(_n(0))._(_n(0)))).toBe(0);
+    });
+
+    it('0 sub 1 is 255', () => {
+      expect($n(sub._(_n(0))._(_n(1)))).toBe(255);
+    });
+
+    it('1 sub 0 is 1', () => {
+      expect($n(sub._(_n(1))._(_n(0)))).toBe(1);
+    });
+
+    it('7 sub 4 is 3', () => {
+      expect($n(sub._(_n(7))._(_n(4)))).toBe(3);
+    });
+
+    it('4 sub 7 is 253', () => {
+      expect($n(sub._(_n(4))._(_n(7)))).toBe(253);
+    });
+  });
+
+  describe('mul', () => {
+    it('0 mul 0 is 0', () => {
+      expect($n(mul._(_n(0))._(_n(0)))).toBe(0);
+    });
+
+    it('0 mul 10 is 0', () => {
+      expect($n(mul._(_n(0))._(_n(10)))).toBe(0);
+    });
+
+    it('10 mul 0 is 0', () => {
+      expect($n(mul._(_n(1))._(_n(0)))).toBe(0);
+    });
+
+    it('1 mul 10 is 10', () => {
+      expect($n(mul._(_n(1))._(_n(10)))).toBe(10);
+    });
+
+    it('10 mul 1 is 10', () => {
+      expect($n(mul._(_n(10))._(_n(1)))).toBe(10);
+    });
+
+    it('3 mul 4 is 12', () => {
+      expect($n(mul._(_n(3))._(_n(4)))).toBe(12);
+    });
+
+    it('100 mul 100 is 12', () => {
+      expect($n(mul._(_n(3))._(_n(4)))).toBe(12);
+    });
+
+    it('0 mul ignores second argument', () => {
+      expect($n(mul._(_n(0))._(undef))).toBe(0);
+    });
+  });
+
+  describe('div', () => {
+    it('0 div 10 is 0', () => {
+      expect($n(div._(_n(0))._(_n(10)))).toBe(0);
+    });
+
+    it('1 div 10 is 0', () => {
+      expect($n(div._(_n(1))._(_n(10)))).toBe(0);
+    });
+
+    it('10 div 1 is 10', () => {
+      expect($n(div._(_n(10))._(_n(1)))).toBe(10);
+    });
+
+    it('10 div 5 is 2', () => {
+      expect($n(div._(_n(10))._(_n(5)))).toBe(2);
+    });
+
+    it('10 div 3 is 3', () => {
+      expect($n(div._(_n(10))._(_n(3)))).toBe(3);
+    });
+
+    it.failing('0 div ignores second argument', () => {
+      expect($n(div._(_n(0))._(undef))).toBe(0);
+    });
+  });
+
+  describe('mod', () => {
+    it('0 mod 10 is 0', () => {
+      expect($n(mod._(_n(0))._(_n(10)))).toBe(0);
+    });
+
+    it('1 mod 10 is 1', () => {
+      expect($n(mod._(_n(1))._(_n(10)))).toBe(1);
+    });
+
+    it('10 mod 1 is 0', () => {
+      expect($n(mod._(_n(10))._(_n(1)))).toBe(0);
+    });
+
+    it('10 mod 5 is 0', () => {
+      expect($n(mod._(_n(10))._(_n(5)))).toBe(0);
+    });
+
+    it('10 mod 3 is 1', () => {
+      expect($n(mod._(_n(10))._(_n(3)))).toBe(1);
+    });
+
+    it.failing('0 mod ignores second argument', () => {
+      expect($n(mod._(_n(0))._(undef))).toBe(0);
+    });
+  });
+
+  describe('show', () => {
+    it('show 0 is "0"', () => {
+      expect($s(show._(_n(0)))).toBe('0');
+    });
+
+    it('show 1 is "1"', () => {
+      expect($s(show._(_n(1)))).toBe('1');
+    });
+
+    it('show 255 is "255"', () => {
+      expect($s(show._(_n(255)))).toBe('255');
+    });
+  });
+});
diff --git a/test/list.spec.ts b/test/list.spec.ts
index 36ff778..ec9a982 100644
--- a/test/list.spec.ts
+++ b/test/list.spec.ts
@@ -154,6 +154,15 @@ describe('List', () => {
     });
   });
 
+  // describe('repeat', () => {
+  //   it('repeat 0 is [0, 0, 0, ...]', () => {
+  //     expect($na(
+  //       repeat._(_n(0))._<List<Num>>(_((x0: Num) => _((x1s: List<Num>) =>
+  //         x1s._<List<Num>>(_((x1: Num) => _((x2s: List<Num>) =>
+  //           x2s._<List<Num>>(_((x2: Num) => _((_xrs: List<Num>): List<Num> => cons._(x0)._(cons._(x1)._(cons._(x2)._(Nil)))))))))))))).toEqual([0, 0, 0]);
+  //   });
+  // });
+
   describe('head', () => {
     it('returns nothing from Nil', () => {
       expect(() => $$(head._(Nil))).toThrow();
diff --git a/tsconfig.json b/tsconfig.json
index f281384..1555b2d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -13,8 +13,6 @@
     "noImplicitOverride": true,
     "noImplicitReturns": true,
     "noImplicitThis": true,
-    "noUnusedLocals": true,
-    "noUnusedParameters": true,
     "strictNullChecks": true,
     "strictPropertyInitialization": true,
     "declaration": false,