Bjorn Lisper <[EMAIL PROTECTED]> writes:
> data LispList t = Atom t | LispList [LispList t] | Str [Char]
>
> instance Show t => Show (LispList t) where
> show (Atom t) = show t
> show (LispList t) = show t
> show (Str t) = show t
>
> hugsprompt> (LispList [Atom 1, Str "HEJ"]) ==> [1,"HEJ"]
> hugsprompt> (LispList [Str "HEJ",Atom 1]) ==> "Cannot find show function...."
>
> So there is a problem when the value is of form Str string or where such a
> value is first in the list l in a value of the form LispList l. Oddly
> enough, such values may appear at other positions without causing any
> problems.
Are you sure about that? I can't reproduce the above results in hugs
(Hugs 98, February 2000) or ghci (5.02). I get a much simpler answer:
if the s-expression includes an Atom term, it works; otherwise you get
a type error. In particular, for the second example above
(LispList [Str "HEJ", Atom 1])
both ghci and hugs produce the expected result, rather than failing.
Carl Witty
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