Constructs an app from a blueprint map with keys:

• :initial-model - Initial model value, must be a map.
• :on-signal - Signal handler. Function of args: [model signal dispatch-signal dispatch-action]. It performs side effects, can dispatch actions and new signals. By convention, it must be able to handle :on-start and :on-stop signals in order to be wrappable by middleware. Read-only model atom is useful for reading actual model values in async code and to subscribe to model changes. Function dispatch-signal returns the result of the underlying on-signal call. Function dispatch-action always returns nil.
• :on-action - Action handler. Pure function of args: [model action]. Given an action and current model value, it must return the new model value.

Returns a map with keys:

• :model - An object that supports IDeref and IWatchable protocols.
• :dispatch-signal - Function with a single arg: a signal to be sent to an app. Returns the result of the underlying on-signal call.

Creates a read-only reference which automatically syncs its value with (f @r). Returned object supports deref, add-watch and remove-watch. Arguments:

• r - source reference, it must support deref, add-watch and remove-watch (e.g. an atom or another read-only reference)
• f - pure function