# Split composition

**Split-compose** is a point-free construct, used to pre-process it's argument(s) with the left, and right-most operand before applying the middle operand between the result.

It's definition is specified as `(F x) G (H y)`

.

In BQN, the construct can be formed using Before `(⊸)`

and After `(⟜)`

, two compositional operators. In this example, we multiply the range of the left argument, with the absolute value of the right.

5 ↕⊸×⟜| 5‿¯8‿¯2‿¯5‿3 ⟨ 0 8 4 15 12 ⟩

Monadically, the right argument can be duplicated and split-compose will be applied asymmetrically, similar to hook

+´⊸÷⟜≠ ↕10 ⟨ 4.5 ⟩ # This is evaluated as (↕10) +´⊸÷⟜≢ ↕10

Monadically, split-compose is precisely equivalent to a fork.

(+´÷≠) ↕10 4.5

In dialects that lack Before, split-compose can be defined differently.

In Dyalog APL you may form the expression with Beside `(∘)`

and Commute `(⍨)`

g∘h⍨∘f⍨

g⍨∘f⍨∘h⍨⍨

For example:

÷⍨∘(+/)⍨∘≢⍨⍨ ⍳10 4.5

Whilst these expressions will return the same results (if the functions f,g, & h are pure) the evaluation order is not identical.

And (most commonly) as a fork:

f⍤⊣ g h⍤⊢

## See also