Module Duppy.Monad

module Monad: sig .. end

Monadic interface to Duppy.Io.

This module can be used to write code that runs in various Duppy's tasks and raise values in a completely transparent way.

You can see examples of its use in the examples/ directory of the source code and in the files src/tools/{harbor.camlp4,server.camlp4} in liquidsoap's code.

When a server communicates with a client, it performs several computations and, eventually, terminates. A computation can either return a new value or terminate. For instance:

Client connects.
Server tries to authenticate the client.
If authentication is ok, proceed with the next step.
Otherwise terminate.

The purpose of the monad is to embed computations which can either return a new value or raise a value that is used to terminate.

type ('a, 'b) t

Type representing a computation which returns a value of type 'a or raises a value of type 'b

val return : 'a -> ('a, 'b) t

return x create a computation that returns value x.

val raise : 'b -> ('a, 'b) t

raise x create a computation that raises value x.

val bind : ('a, 'b) t ->
       ('a -> ('c, 'b) t) -> ('c, 'b) t

Compose two computations. bind f g is equivalent to: let x = f in g x where x has f's return type.

val (>>=) : ('a, 'b) t ->
       ('a -> ('c, 'b) t) -> ('c, 'b) t

>>= is an alternative notation for bind

val run : return:('a -> unit) -> raise:('b -> unit) -> ('a, 'b) t -> unit

run f ~return ~raise () executes f and process returned values with return or raised values with raise.

val catch : ('a, 'b) t ->
       ('b -> ('a, 'c) t) -> ('a, 'c) t

catch f g redirects values x raised during f's execution to g. The name suggests the usual try .. with .. exception catching.

val (=<<) : ('b -> ('a, 'c) t) ->
       ('a, 'b) t -> ('a, 'c) t

=<< is an alternative notation for catch.

val fold_left : ('a -> 'b -> ('a, 'c) t) ->
       'a -> 'b list -> ('a, 'c) t

fold_left f a [b1; b2; ..] returns computation (f a b1) >>= (fun a -> f a b2) >>= ...

val iter : ('a -> (unit, 'b) t) -> 'a list -> (unit, 'b) t

iter f [x1; x2; ..] returns computation f x1 >>= (fun () -> f x2) >>= ...

module Mutex: sig .. end

This module implements monadic mutex computations.

module Condition: sig .. end

This module implements monadic condition computations.

module Io: sig .. end

This module implements monadic computations using Duppy.Io.