Aha. It is indeed true that
ghc -fdefer-type-errors -w
does not suppress the warnings that arise from the type errors; indeed there is no current way to do so. How to do that?
To be kosher there should really be a flag to switch off those warnings alone, perhaps
-fno-warn-type-errors
So then -fwarn-type-errors is on by default, but is only relevant when -fdefer-type-errors is on. Once -fdefer-type-errors is on, -fno-warn-type-errors and -fwarn-type-errors suppress or enable the warnings. -w would then include -fno-warn-type-errors.
Is that a design everyone would like? If so, woudl someone like to open a ticket, implement it, update the documentation, and send a patch?
many thanks
Simon
| -----Original Message-----
| From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-
| bounces@haskell.org] On Behalf Of Richard Eisenberg
| Sent: 11 March 2013 13:28
| To: Kazu Yamamoto (山本和彦)
| Cc: glasgow-haskell-users@haskell.org
| Subject: Re: runghc -fdefer-type-errors
|
| When I ran this code (ghc 7.6.1), I did get the Hello, world! printout. That line
| was sandwiched between the compile-time warning from the type error and the
| run-time exception from the type error, but the output was there:
|
| 09:24:28 ~/temp> runghc Scratch.hs
|
| Scratch.hs:5:12: Warning:
| No instance for (Num String) arising from the literal `1'
| Possible fix: add an instance declaration for (Num String)
| In the first argument of `putStrLn', namely `1'
| In a stmt of a 'do' block: putStrLn 1
| In the expression:
| do { putStrLn "Hello, world";
| putStrLn 1 }
| Hello, world
| Scratch.hs: Scratch.hs:5:12:
| No instance for (Num String) arising from the literal `1'
| Possible fix: add an instance declaration for (Num String)
| In the first argument of `putStrLn', namely `1'
| In a stmt of a 'do' block: putStrLn 1
| In the expression:
| do { putStrLn "Hello, world";
| putStrLn 1 }
| (deferred type error)
|
|
| It's easier to see with `runghc Scratch.hs 2> /dev/null` which prints only the
| Hello, world! Oddly, passing flag "-w" doesn't suppress the warning, so I don't
| think there's a way to turn it off.
|
| Richard
|
| On Mar 11, 2013, at 3:45 AM, Kazu Yamamoto (山本和彦)