I have this typeclass: class Monad m => Convertible m a b where convert :: a -> m b For many pairs of types, the conversion can be done purely, without requiring a monadic effect. Now, I kn...

The base library in Haskell has the following type synonyms in Data.Semigroup: type ArgMin a b = Min (Arg a b) type ArgMax a b = Max (Arg a b) Here are links to the haddocks: ArgMin and ArgMax W...

I need to do something similar to the CASE WHEN .. OR .. THEN from SQL in python for STRINGS. For example, if I say "DOG" or "CAT".. my translation is "ANIMAL". I don't want to use IF ELIF ELIF.. ...

I'm going over continuations and I've come across two different approaches to structuring continuation types: newtype C r a = C {runC :: (a -> r) -> r} exampleFunction :: String -> C Boo...

I am getting a strange error about a data type being "not in scope" when using Template Haskell. Here is my Main.hs file: {-# LANGUAGE TemplateHaskell #-} module Main where import Control.Lens ...

I have two functions for controlling loops, continue and break: type Control a = (a -> a) -> a -> a continue :: Control a continue = id break :: Control a break = const id Then, I wan...

If I have a type with a phantom parameter that I only sometimes care about, like this one: data Foo p a b = Bar a b Is there any hack way to write a type synonym Baz such that Baz a b is Foo p a...

Apparently a bit absent-mindedly, I wrote something like the following: {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE TypeFamilies #-} class Foo f where type Bar f :: * retbar :: Bar f -> IO...