On Thu, 3 Jan 2008, Peter Verswyvelen wrote:
I believe type signatures are the very essence of Haskell documentation! I'd much rather see a program with type signatures for functions and little (or no) comments over programs with no type signatures and ambigious comments (if any comments at all!).
Okay, but when using a syntax directed editor, type signatures can be automatically provided because the types are known.
Types cannot always be derived automatically, especially when coming to Haskell extensions. Sometimes you also want to restrict the type. E.g. for asTypeOf _ y = y you explicitly want the type asTypeOf :: a -> a -> a not the automatically derived one: asTypeOf :: b -> a -> a
Furthermore, IMHO, type signatures alone are not enough, a good parameter name says at least as much as the type.
E.g. what does a function Int -> Int -> Bool do? I have no idea. A good function name helps, e.g. isDivisible:: Int -> Int -> Bool. But then I still don't know which parameter is the numerator and denominator. So good names for the parameters are at least as important, e.g. isDivisible :: numerator:Int -> denonimator:Int -> Bool
It's a problem in Haskell that there are no unique parameter names, due to pattern matching. E.g. isDivisible _ 0 = error "division by zero" isDivisible x y = ... I'm tempted to write Haddock comments like {- | check whether @x@ can be divided by @y@ -} isDivisible :: Integral a => a -> a -> a But this does not work, because unique parameter names cannot be extracted from the code and are thus missing in Haddock documentation. If there would not be pattern matching but only 'case' there wouldn't be a problem. isDivisible x y = case (x,y) of (_,0) -> error "division by zero" (x',y') -> ... Or even better, with a fictitious anonymous 'case' you could write: isDivisible = curry $ case (_,0) -> error "division by zero" (x,y) -> ...
Type signatures really does make dealing with someone elses code that much easier.
Yes, as is good documentation, which unfortunately is still limited to ASCII. I would prefer to have rich documentation right inside my source code, with math symbols, drawings, pictures, animations, whatever...
... interactive Haskell sandbox ...