CODEWITHSUNDEEP
haskell
xcoder
xcoder

Reputation: 1436

Haskell define a datatype

I am learning Haskell an come across something like the following:

data ABC :: * where
 Empty :: ABC
 Single :: Char -> ABC

what does the above mean? And what does it mean when we say "write a ABC representing something"?

Upvotes: 1

Views: 340

Answers (1)

J. Abrahamson
J. Abrahamson

Reputation: 74354

This syntax is identical to the standard datatype syntax in Haskell. In particular, the type ABC is the same as

data ABC = Empty | Single Char

The syntax including the where clause is called "GADT syntax" and it offers some extra expressiveness by allowing clear syntax for "existential types" and "type equalities". Both of these are rather advanced topics, though. Stick with basic types until you get your water legs.

Upvotes: 2

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