caseof

A simple way to query constructors, like cases but slightly more concise.

Prisms from the lens package can also manage this, but this is a bit simpler.

Aimed at sum types with many constructors:

data Wiggle = Woo Int Char | Wibble Int deriving Show

There is a case predicate:

> $(isCaseOf 'Woo) (Woo 5 'a')
True

There is a Maybe-based matcher:

> $(maybeCaseOf 'Woo) (Woo 1 'a')
Just (1,'a')

There is a "map" over a constructor:

> $(mapCaseOf 'Left) succ (Left 3)
Left 4

There is a combinator which calls your function with n arguments, or passes the whole value to an "else" clause.

> $(caseOf 'Woo) (\x y -> show x ++ show y) (const "") (Wibble 5)
""

Use in your project

In your stack.yaml, put:

extra-deps:
- git: https://github.com/chrisdone/caseof.git
  commit: 9a7f6bb