Re: [Haskell-cafe] Printing the empty list.

On 1 July 2011 08:58, Joshua Ball wrote:

GHCi seems to be clever about some things:

If I try to print the empty list in ghci, I encounter no problems:

Prelude> [] [] Prelude> show [] "[]" Prelude> print [] []

Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of "")?

Type defaulting: if you don't specify a type, then ghci makes it [Integer].

If I write a program in a file and load it in

main = print []

Then I get the ambiguous type variable error that I would expect. Why doesn't ghci generate this error at the prompt?

Because ghc doesn't do type defaulting. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com