Proposal: Add Text.Read.maybeRead :: Read a => String -> Maybe a

Jeff Polakow jeff.polakow at
Fri Feb 8 13:24:30 EST 2008


> readM with fail defaults to ioError for almost all Monads, and so admits
> many dangerous programs, which is against the intent of the proposal 
> in the first place.
ioError is only in the IO monad and is catchable. I think the problem is 
when fail defaults to error which can be anywhere and is not catchable. 

> It seems with Conor's suggestion of a 
>     maybeReturn :: MonadPlus m => Maybe a -> m a
>     maybeReturn = maybe mzero return
> we can still have the by-default-safe maybeRead, that doesn't admit 
> exception throwing opportunities.
Isn't the MonadPlus approach also by-default-safe?



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