[Haskell-beginners] how to skip pattern match error when applying a mapM_

PICCA Frederic-Emmanuel frederic-emmanuel.picca at synchrotron-soleil.fr
Tue Jan 17 20:46:32 UTC 2017

> You just look at the Monad instance for the type. IO is a bit special, but
> here is the one for Maybe[1].

thanks and what is the purpose of 

fail _ = nothing



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