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
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 Dienerstr. 12, 80331, München
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