On 2016-01-05 at 08:59, Olumide <50295@web.de> wrote:
On 01/01/2016 19:41, Alexander Berntsen wrote:
Here we use [] both on type and term level. On type level we use it to mean a list of 'a's, and on term level we use it to mean the empty list.
Out of curiosity, is [] defined as type constructor _and_ term level at the library level or in the language/compiler? (BTW, google tells me "term-level" has a special meaning that I do not yet know.)
The special syntax of [] requires that the compiler (specifically, the parser) treat lists specially. We could define our own data type that behaves like lists, List a = Nil | Cons a (List a) but writing out literal lists would be a little clunky. It's nice that we can write: [] [1] [1,2,3] instead of: Nil Cons 1 Nil Cons 1 (Cons 2 (Cons 3 Nil)) The [1,2,3] syntax requres that the Haskell parser be aware of this type. At the type level, we can write [Int], [Char], and so forth, instead of List Int, List Char. This also requires support in the parser. bergey