Lambda Case GHC Extension

Note

One of my favourite extensions to GHC (the most prominent Haskell compiler) is LambdaCase. It allows you to shorten a case expression in Haskell by quite a bit. Let's see how.

A case expression usually looks like this:

data Colour = Red | Green | Blue

printColour :: Colour -> Text
printColour colour = case colour of
  Red -> "red"
  Green -> "green"
  Blue -> "blue"

See those two uses of the colour identifier? That's a bit too much at times, especially with nested cases.

Let's see how we can shorten it with LambdaCase.

{-# LANGUAGE LambdaCase #-}

data Colour = Red | Green | Blue

printColour :: Colour -> Text
printColour = \case
  Red -> "red"
  Green -> "green"
  Blue -> "blue"

Since well written type signatures can convey the meaning of a function well enough, the more concise syntax here doesn't sacrifice readibility in my opinion.

I'll dig into how it's implemented in future notes. I just wanted to highlight its usage here.

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