runghc -fdefer-type-errors

Isaac Dupree ml at
Tue Mar 12 03:33:46 CET 2013

On 03/11/2013 07:04 PM, Simon Peyton-Jones wrote:
> 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.

GCC has a concept -Werror=unused-variable for example: each
warning can be disabled, a warning, or an error.  If GHC had that, we
could have "type-errors" be a warning whose default state is -Werror.
That's cleaner in a certain way, but it also seems fishy.  Just
throwing the idea out there.


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