The Template Haskell quotation monad (Q) has proper support for fail:
module A where
import Language.Haskell.TH
foo :: Q Exp
foo = fail "Custom compile error!"
and
module B where
import A
main :: IO ()
main = print $foo
gives
B.hs:6:14:
Custom compile error!
In the first argument of `print', namely `$foo'
In the expression: print ($foo)
In an equation for `main': main = print ($foo)
-E
On Fri, Aug 9, 2013 at 9:48 AM, Jose A. Lopes <[email protected]> wrote:
> Hi,
>
> In Template Haskell, what is the proper way of signalling an error ?
>
> For example, you are generating code and you detect that a given
> parameter does not fulfill a precondition (e.g., String is empty), and
> you want to abort compilation with a descriptive error message.
>
> Thanks,
> Jose
>
> --
> Jose Antonio Lopes
> Ganeti Engineering
> Google Germany GmbH
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