I'm following this answer to learn how to pattern match on Sequences. For concreteness, imagine that I'm implementing breadth-first search over a 2-d grid using a Sequence as a queue. Using just Vi...

To start off this whole thing I'm working with a pattern synonym defined as follows: {-# Language PatternSynonyms #-} pattern x := y <- x @ y This allows me to run multiple pattern matches acr...

With PatternSynonyms (explicitly bidirectional form), the pattern-to-expr equations in effect form a function but spelled upper-case (providing you end up with an fully saturated data constr of the...

I have the following code and I don't know what should feed at ??. Or cannot polymorphic patterns make complete? {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE ViewPatterns #-} module Data.Tuple.S...

Is it possible to use list style pattern matching on vectors? ie import qualified Data.Vector as V f :: V.Vector a -> a f (x:xs) = x gives an error

I'm trying to create a pattern synonym for a newtype with an empty map. {-# Language PatternSynonyms #-} import qualified Data.Map as Map newtype StoreEnv = StoreEnv (Map.Map Int String) derivi...

Consider the following data type and pattern synonyms: {-# LANGUAGE PatternSynonyms, NamedFieldPuns #-} data Foo = Foo { a :: Int , b :: String , c :: Maybe Bool } pattern Bar a b <- Foo {...

Say I want to implement the length function for lists using pattern matching, then I could do something like this: length' :: (Num b) => [a] -> b length' [] = 0 length' (_:xs) = 1 + length...

I'm getting an error when trying to define a pattern synonym based on a GADT that has a type-level list. I managed to boil it down to this example: {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatu...

{-# LANGUAGE PatternSynonyms, ViewPatterns #-} data Quun = Foo | Bar | Oink Quun fooey :: Quun -> Bool fooey Foo = True fooey (Oink Yum) = True fooey _ = False pattern Yum <- (fooey -> ...

I'm writing a simple ADT for grid axis. In my application grid may be either regular (with constant step between coordinates), or irregular (otherwise). Of course, the regular grid is just a specia...

I am using Data.Sequence instead lists for better performance. With lists we can do the following foo :: [Int] -> Int foo [] m = m foo (x:xs) m = ... How can this be accomplished with Data.Se...

Does some standard Haskell library define a data type like this data ListWithEnd e a = Cons a (ListWithEnd e a) | End e That is a list whose terminating element carries a value of a designated ...

I’m working on a library allowing a developper to control a Minitel (the french videotex terminal). I have a lot of constant values and I would like to know the best way to manage them with Haskel...

I've managed to construct the following "minimal" example that shows my problem. Provided the PatternSynonyms extension is enabled data Vec = Vec Int Int pattern Ve x y = Vec x y f :: (Vec, Vec...

I'm a Haskell newbie, and having a bit of trouble figuring out how to pattern match a ByteString. The [Char] version of my function looks like: dropAB :: String -> String dropAB [] = [] dropAB ...

Is there a way to have something equivalent to creating "constructor aliases" in Haskell? I'm thinking similar to type aliases where you can give the type a different name but it still behaves in e...