Petr, Of course you are right. :-: is a value constructor (function) albeit declared in the infix style a :-: (List a). Thanks, - Olumide On 21/12/15 19:00, Petr Vápenka wrote:
Hello,
actually the definition with data keyword is right there:
infixr 5 :-: data List a = Empty | a :-: (List a) deriving (Show, Read, Eq, Ord)
it could be written in prefix form as
data List a = Empty | Cons a (List a) deriving (....)
Petr
On Mon, Dec 21, 2015 at 7:56 PM, Olumide <50295@web.de mailto:50295@web.de> wrote:
Hello,
On chapter 7 of LYH there's an example of a user-defined operator .++
infixr 5 .++ (.++) :: List a -> List a -> List a Empty .++ ys = ys (x :-: xs) .++ ys = x :-: (xs .++ ys)
which is used as follows
let a = 3 :-: 4 :-: 5 :-: Empty let b = 6 :-: 7 :-: Empty a .++ b (:-:) 3 ((:-:) 4 ((:-:) 5 ((:-:) 6 ((:-:) 7 Empty))))
Following this the text reads:
"Notice how we pattern matched on (x :-: xs). That works because pattern matching is actually about matching constructors. We can match on :-: because it is a constructor for our own list type ..." Source: http://learnyouahaskell.com/making-our-own-types-and-typeclasses#recursive-d...
Is the operator :-: a constructor? I'm confused because the definition of :-: is not prefixed by the data keyword?
- Olumide
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