codewars

codewars solutions

Solutions to exercises from codewars.com.

I'll only list here non trivial solutions to exercices that I have not authored. Difficulty ranking ranges from 8kyu (easiest) to 1kyu (hardest). Most of the files will not compile on their own. A lot of the work has been done in-browser and the code isn't always well formatted/documented.

1 Kyu

Coroutines (Haskell)

Implementation of a coroutine library (pipeline of functions that can yield values repeteadly or request input).
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Scott Encoding (Haskell)

Implementation of basic algebraic data structures using Scott Encoding.
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Sure, but can you SKI (Haskell)

Basic operators of the SKI combinator calculus + implementation of several common combinators & boolean arithmetic in point free form.
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One function, many arguments: Haskell style

(Clumsy) implementation of a few polyvariadic functions (functions that can take a variable number of arguments).
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Peano and Church (Haskell)

Formulation of natural numbers using Church, Peano and Scott encoding, as well as representation as a list of units.
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Lensmaker (Haskell)

A mini-library of van Laarhoven style lenses.
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2 Kyu

Yoneda Lemma (Haskell)

Proof of the Yoneda Lemma in Hask, with some light application to counting instances of natural transformations.
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Count them all! (Haskell)

Fun with the cardinality of types: count and enumerate all members of given types, including function and functor types.
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Symbolic differentiation of prefix expression (Haskell)

I like this one. Parses a mathematical expression in prefix expression then computes its derivative and simplifies it.
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Finally tagless interpreter (Haskell)

Interpreter for a finally tagless EDSL.
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Odd + Even = Odd? Prove it! (Haskell)

(Ab)use of the Haskell type system to prove some properties of arithmetic on even and odd integers.
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Algebraic Isomorphism (Haskell)

Using the isomorphism between algebraic data types to do some light proof work.
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Regular expression parser (Haskell)

A simple regular expression parser. The implementation is a bit messy.
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I love Lisp (Haskell)

A parser and interpreter for a simple Lisp-like language.
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Writing applicative parsers from scratch (Haskell)

Everything is in the title.
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Singletons (Haskell)

Implementation of a compile-time checked vector using features mimicking dependent types.
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The most imperative functional language? (Haskell)

Imperative syntax in do notation using the State monad.
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3 Kyu

Magic compare (C++)

A simple class that allow three way comparisons (a < b < c) in C++.
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Constructing finite fields using binary polynoms (Haskell)

Definition of the binary polynom field and ring and their operations.
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Battleship field validator (C++)

Checks that the positions of ships on a board of Battleship are legal.
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Isomorphism (Haskell)

Definition of some isomorphisms using the Haskell type system.
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4 Kyu

Five fundamentals monads (Haskell)

Implementation of Identity, Maybe, State, Reader and Writer.
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