[Haskell-beginners] Defaulting the following constraint ....

[Brandon Allbery]

On Thu, Oct 3, 2013 at 1:52 PM, Alan Buxton <alanbuxton at gmail.com> wrote:

> niceShow x = if isInt x then show (floor x :: Int) else show x
>
> ** **
>
> I get a warning about a ?too strict if?. If I then follow the
> recommendation and change niceShow to be****
>
> ** **
>
> show (if isInt x then (floor x :: Int) else x)****
>
> ** **
>
> Then I get an error that *Couldn't match expected type `Int' with actual
> type `Double'*   which makes sense because floor x :: Int produces an Int
> but x alone is a Double. Surely hlint could have figured this out from the
> type signatures and not made the recommendation to change my if structure?
> ****
>
> **
>

hlint doesn't recognize types, only code structure to some extent (it is a
parser, not a compiler). As such, it will sometimes produce bad advice like
that.

"Too strict if" pretty much means what you saw... that you have the same
structure in both legs and it thinks you should abstract it out. But, as I
noted, it doesn't know about types so it can't recognize that you can't
type the refactored expression. In fact I'd generally claim that "Too
strict if" is by far its worst designed diagnostic, because of its
inability to recognize types and because the resulting message is
incomprehensible.

In short, take hlint's diagnostics with several grains of salt.

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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