Type signatures as good style
(signatures are good documentation and cannot always be infered automatically)
(mention rank n types)
Revision as of 20:55, 8 July 2008
Since Haskell type checkers can automatically derive types of expressions why shall I put explicit type signatures in my programs?
Using explicit type signatures is good style and GHC with option
-Wall warns about missing signatures.
Signatures are a good documentation and not all Haskell program readers have a type inference algorithm built-in.
There are also some cases where the infered signature is too general for your purposes.
emptyString :: ShowS emptyString = id
I remember that for some type extensions the automatic inference fails. Examples?Higher-order types, e.g., the type of
runST :: (forall s . ST s a) -> a
cannot be inferred in general, because the problem is undecidable. In GHC, they are enabled with the language pragma
3 How to add a bunch of signatures?
Ok, this convinced me. How can I add all the signatures I did not write so far?