Module handler_compose 

Effect-handler composition primitive (P-1.0-V1.2).

Builds a single handler from two: the composed handler discharges the union of the two handlers’ effect rows.

Algebraic laws (proven by tests below):

• Associativity: compose(a, compose(b, c)) == compose(compose(a, b), c).
• Commutativity: compose(a, b) == compose(b, a) (handlers are modeled as effect rows; row-union is commutative).
• Identity: compose(a, identity) == a where identity is the empty-row handler.
• Idempotence on equal handlers: compose(a, a) == a.
• Apply-compose distributivity: handler_apply(row, compose(a, b)) == handler_apply(handler_apply(row, a), b).

Functions

handler_compose

Compose two handlers. The result discharges every effect kind in either input handler.