I think Herbert's monadic version of "clunky" is really satisfactory :
>clunky env var1 var2 = fromJust (do val1 <- lookup var1 env
> val2 <- lookup var2 env
> return (var1 + var2)
> ++
> Just (var1 + var2)
A similar solution which avoids using "Just" and "fromJust" (and with
monad comprehension instead of "do") is:
>clunky env var1 var2 =
> fromMaybe (var1 + var2)
> [val1 + val2 | val1 <- lookup var1 env
> , val2 <- lookup var2 env]
(fromJust and fromMaybe are functions from the standard library Maybe)
Both solutions are obtained without any extension to haskell (1.4)
and I think they are as clear as the guarded-pattern version.
Does somebody know another illustrative example which cannot be
solved with monadic operators?
Guille
