Universum.VarArg

Provides operator of variable-arguments function composition.

Documentation

class SuperComposition a b c | a b -> c where

This type class allows to implement variadic composition operator.

Methods

(...) :: a -> b -> c infixl 8

Allows to apply function to result of another function with multiple arguments.

>>> (show ... (+)) 1 2
"3"
>>> show ... 5
"5"
>>> (null ... zip5) [1] [2] [3] [] [5]
True

Inspired by http://stackoverflow.com/questions/9656797/variadic-compose-function.

Performance

To check the performance there was done a bunch of benchmarks. Benchmarks were made on examples given above and also on the functions of many arguments. The results are showing that the operator (...) performs as fast as plain applications of the operator (.) on almost all the tests, but (...) leads to the performance draw-down if ghc fails to inline it. Slow behavior was noticed on functions without type specifications. That's why keep in mind that providing explicit type declarations for functions is very important when using (...). Relying on type inference will lead to the situation when all optimizations disappear due to very general inferred type. However, functions without type specification but with applied INLINE pragma are fast again.

Instances

(a ~ c, r ~ b) => SuperComposition (a -> b) c r

Defined in Universum.VarArg

Methods

(...) :: (a -> b) -> c -> r

(SuperComposition (a -> b) d r1, r ~ (c -> r1)) => SuperComposition (a -> b) (c -> d) r

Defined in Universum.VarArg

Methods

(...) :: (a -> b) -> (c -> d) -> r