Newtype
Revision as of 20:33, 2 September 2006 by NeilMitchell (talk | contribs)
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.
One frequent question is what is the difference between data and newtype? The answer has to do with the level of undefinedness that occurs in the values. The following sample code shows how three different data declarations behave with undefined present.
module Foo where
data Foo1 = Foo1 Int
data Foo2 = Foo2 !Int
newtype Foo3 = Foo3 Int
x1 = case Foo1 undefined of
Foo1 _ -> 1 -- 1
x2 = case Foo2 undefined of
Foo2 _ -> 1 -- undefined
x3 = case Foo3 undefined of
Foo3 _ -> 1 -- 1
y1 = case undefined of
Foo1 _ -> 1 -- undefined
y2 = case undefined of
Foo2 _ -> 1 -- undefined
y3 = case undefined of
Foo3 _ -> 1 -- 1