# Coerce for constant time newtype lists

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haskell has a coerce function. It’s pretty cool!

in the haskell wiki, it talks about how `newtype`

s incur no runtime cost, but
when you have an array of newtypes, a runtime cost will still happen in order to
instantiate the array of newtypes. Basically, a linear operation of noops will
occur. This can be avoided by using `coerce`

.

```
import Data.Monoid
import Data.Coerce
-- Without coerce, a linear cost:
x, y, z :: Sum Int
x = [Sum 1, Sum 7, Sum 10000]
-- which is basically the same as:
y = map Sum [1,7,10000 :: Int]
-- With coerce, it becomes an O(1) operation:
z = coerce [1,7,10000 :: Int]
```