package middleware

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Module MiddlewareSource

A "middleware" function is one which runs before, after, and possibly instead of another function.

Middleware can be composed, in order to create a chain of wrapping invocations.

Note that a middleware function can not be called on its own. It is required to be "terminated" by a conventional function.

Sourcemodule type MONAD = sig ... end

Minimal monad definition required by a Middleware.

Sourcemodule type MONAD2 = sig ... end

Monads of two type parameters.

Sourcemodule Monads : sig ... end

Some common monads.

Sourcemodule Make (M : MONAD) : sig ... end

Creates a Middleware module, providing effects with the given Monad.

Sourcemodule Make2 (M : MONAD2) : sig ... end

Creates a Middleware module, providing effects with the given two-parameter Monad.

Middleware backed by the identity monad.

include sig ... end
Sourcemodule Diverter : sig ... end
Sourceval stop : 'output Monads.Identity.t -> ('a, 'b, 'output) Diverter.t

stop x creates a Stop Diverter with the return value x.

Sourceval continue : 'next_input -> ('next_output -> 'output Monads.Identity.t) -> ('next_input, 'next_output, 'output) Diverter.t

continue next_input fn creates a Continue diverter, passing next_input to the subsequent Middleware g. fn is applied to the value returned by g.

Sourcetype (!'input, !'next_input, !'next_output, !'output) t = 'input -> ('next_input, 'next_output, 'output) Diverter.t

A function which composes with other Middleware functions. Composed Middleware can respond to the return value of Middleware running later. When a Middleware function f runs, it either:

  • Stops, and returns a result
  • Continues by allowing the next middleware function g to run
  • After g runs, control returns to f, where f can respond to g's result and change its own return value.
Sourceval terminate : ('ai, 'bi, 'bo, 'ao) t -> ('bi -> 'bo Monads.Identity.t) -> 'ai -> 'ao Monads.Identity.t

terminate ma fb terminates Middleware ma by providing a function fb which does not delegate. In order to turn a Middleware chain into a function, it must be terminated by a non-delegating function using terminate.

Sourceval compose : ('ai, 'bi, 'bo, 'ao) t -> ('bi, 'ci, 'co, 'bo) t -> ('ai, 'ci, 'co, 'ao) t

compose ma mb composes two Middleware functions. When run, ma first runs, giving mb the option to continue later on. Note that a composed Middleware still need to be terminated via terminate to be called.

Sourcemodule Infix : sig ... end