| Gentle Haskellers,
|
| Here's a Haskell98-typo question.
|
| Consider this program:
|
| module M where
|
| reverse xs = Prelude.reverse (tail xs)
|
| foo ys = M.reverse ys
|
| This is legal Haskell98. The call to Prelude.reverse and to M.reverse
| must both be qualified, because plain 'reverse' would be ambiguous.
| But the definition of reverse does not need to be qualified, becuase it's
| a definition!
|
|
| Now, would it be legal to add this type signature to the end of M?
|
| reverse :: [a] -> [a]
|
| Or should it be
|
| M.reverse :: [a] -> [a]
|
| I can see two arguments
|
| A) The unqualified form should be legal because the type signature
| can only refer to the 'reverse' defined in this module
|
| B) The unqualified form is ambiguous. All occurrences of 'reverse',
| other than the definition itself, must be qualified
|
| The Report itself does not answer the question clearly,
| so I propose to resolve the ambiguity.
|
| Personally I'm inclined to resolve it in favour of (B). In due course we
| may want to allow type signatures for imported things in a module, for
| example. Does anyone object?
Since it's a Haskell 98 issue, I am in favour of (A):
reverse :: reverse :: [a] -> [a]
reverse xs = Prelude.reverse (tail xs)
Alternative (B) looks rather ugly:
M.reverse :: reverse :: [a] -> [a]
reverse xs = Prelude.reverse (tail xs)
Cheers, Ralf
