Coercions

"I have a Float but want a Double". Or: I have a String but want a Text.

Answer

Usually one can find the right function via Hoogle:

However, a more convenient option is to use the Witch library, which abstracts coercions using a single function, called into:

{-# LANGUAGE TypeApplications #-} -- (1)!

import Witch -- (2)!


float :: Float
float = 4

double :: Double
double = into @Double float -- (3)!

str :: String
str = "hello"

text :: Text
text = into @Text str

1. Only needed if you aren't using GHC2021.

2. This is a library for performing coercions.

3. The use of the @Double here directs helps the type checker infer the output type of into. Only needed if you don't supply the type signature double :: Double.

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