logo       

RE: incorrect type error message: msg#00056

lang.haskell.glasgow.bugs

Subject: RE: incorrect type error message

Your wish is my command

| > The reason there's an error message at all is because of the
| > monomorphism restriction. So that's not surprising.
| > Can you suggest a better error message? I'm always looking for ways
to
| > report errors more informatively.
|
| It may be hard to do, but it would be helpful in cases like this for
| the error to mention the fact that the monomorphism restriction has
fired.
| Connecting the fact that the restriction has been applied and the
particular
| error may be a challenge. Just a thought.


module Foo where
e = fmap id 1

cam-02-unx:~/tmp$ $gpj -c Foo.hs

Foo.hs:5:
No instance for (Num (f a))
arising from the literal `1' at Foo.hs:5
Probable cause: the monomorphism restriction applied to the
following:
e :: f a (bound at Foo.hs:5)
In the second argument of `fmap', namely `1'
In a right-hand side of function `e': fmap id 1


<Prev in Thread] Current Thread [Next in Thread>
Google Custom Search

News | FAQ | advertise