Looking at the source code [1], Read is derived, and not using parseVersion (which has the behaviour I think you expect). You may want to use parseVersion directly. [1]: https://hackage.haskell.org/package/base-4.15.0.0/docs/src/Data-Version.html On Sat, Aug 14, 2021, 11:55 Andreas Abel wrote:

How is the parser for Data.Version supposed to work?

```haskell import Data.Version

readVersion :: String -> Version readVersion = read

main :: IO () main = print $ readVersion "8.10.5"

-- *** Exception: Prelude.read: no parse ```

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On Sat, Aug 14, 2021 at 06:53:08PM +0200, Andreas Abel wrote:

How is the parser for Data.Version supposed to work?

```haskell import Data.Version

readVersion :: String -> Version readVersion = read

main :: IO () main = print $ readVersion "8.10.5"

-- *** Exception: Prelude.read: no parse ```

The Read instance is derived https://hackage.haskell.org/package/base-4.15.0.0/docs/src/Data-Version.html... so it behaves like any other derived Read instance: Prelude Data.Version> read "Version {versionBranch = [8,10,5], versionTags = []}" :: Version Version {versionBranch = [8,10,5], versionTags = []} Tom