[parenthesis]

Because it is more difficult to make a change that affects other code without a change in types occurring, which will make compilation fail until all affected code is updated.

[garethrowlands]

Though Haskell has the option to defer type errors to runtime, making them just warnings at compile time.

It means you can run your unit tests without having to change everything everywhere all at once.

The flag is -fdefer-type-errors