@@ -1,6 +1,8 @@
2navhome: /docs/
2navhome: /docs/
6# Arvo internals
8# Arvo internals
@@ -11,13 +13,13 @@ Arvo is composed of modules called vanes:
14−At a high level `%arvo` takes a mess of unix io events and turns them
16+At a high level `%arvo` takes a mess of Unix I/O events and turns them
15into something clean and structured for the programmer.
17into something clean and structured for the programmer.
17`%arvo` is designed to avoid the usual state of complex event networks:
19`%arvo` is designed to avoid the usual state of complex event networks:
18event spaghetti. We keep track of every event's cause so that we have a
20event spaghetti. We keep track of every event's cause so that we have a
19clear causal chain for every computation. At the bottom of every chain
21clear causal chain for every computation. At the bottom of every chain
20−is a unix io event, such as a network request, terminal input, file
22+is a Unix I/O event, such as a network request, terminal input, file
21sync, or timer event. We push every step in the path the request takes
23sync, or timer event. We push every step in the path the request takes
22onto the chain until we get to the terminal cause of the computation.
24onto the chain until we get to the terminal cause of the computation.
23Then we use this causal stack to route results back to the caller.
25Then we use this causal stack to route results back to the caller.
@@ -29,7 +31,7 @@ The `%arvo` causal stack is called a `++duct`. This is represented
29simply as a list of paths, where each path represents a step in the
31simply as a list of paths, where each path represents a step in the
30causal chain. The first element in the path is the first letter of
32causal chain. The first element in the path is the first letter of
31whichever vane handled that step in the computation, or the empty span
33whichever vane handled that step in the computation, or the empty span
34Here's a duct that was recently observed in the wild:
36Here's a duct that was recently observed in the wild:
@@ -44,20 +46,20 @@ Here's a duct that was recently observed in the wild:
44This is the duct the timer vane receives when "timer" sample app asks
46This is the duct the timer vane receives when "timer" sample app asks
45the timer vane to set a timer. This is also the duct over which the
47the timer vane to set a timer. This is also the duct over which the
46response is produced at the specified time. Unix sent a terminal
48response is produced at the specified time. Unix sent a terminal
47−keystroke event (enter), and arvo routed it to %dill(our terminal),
49+keystroke event (enter), and Arvo routed it to `%dill` (our terminal),
48−which passed it on to the %gall app terminal, which sent it to shell,
50+which passed it on to the `%gall` app terminal, which sent it to shell,
49its child, which created a new child (with process id 4), which on
51its child, which created a new child (with process id 4), which on
50startup asked the timer vane to set a timer.
52startup asked the timer vane to set a timer.
52The timer vane saves this duct, so that when the specified time arrives
54The timer vane saves this duct, so that when the specified time arrives
53−and unix sends a wakeup event to the timer vane, it can produce the
55+and Unix sends a wakeup event to the timer vane, it can produce the
54response on the same duct. This response is routed to the place we
56response on the same duct. This response is routed to the place we
55popped off the top of the duct, i.e. the time app. This app produces the
57popped off the top of the duct, i.e. the time app. This app produces the
56text "ding", which falls down to the shell, which drops it through to
58text "ding", which falls down to the shell, which drops it through to
57the terminal. Terminal drops this down to dill, which converts it into
59the terminal. Terminal drops this down to dill, which converts it into
58−an effect that unix will recognize as a request to print "ding" to the
60+an effect that Unix will recognize as a request to print "ding" to the
59screen. When dill produces this, the last path in the duct has an
61screen. When dill produces this, the last path in the duct has an
60−initial element of the empty span, so this is routed to unix, which
62+initial element of the empty span, so this is routed to Unix, which
61applies the effects.
63applies the effects.
63This is a call stack, with a crucial feature: the stack is a first-class
65This is a call stack, with a crucial feature: the stack is a first-class
@@ -90,42 +92,42 @@ caller.
93−As shown above, we use arvo proper to route and control the flow of
95+As shown above, we use Arvo proper to route and control the flow of
94−moves. However, arvo proper is rarely directly responsible for
96+moves. However, Arvo proper is rarely directly responsible for
95processing the event data that directly causes the desired outcome of a
97processing the event data that directly causes the desired outcome of a
96move. This event data is contained within a card, which is simply a
98move. This event data is contained within a card, which is simply a
97−`(pair term noun)`. Instead, arvo proper passes the card off to one of
99+`(pair term noun)`. Instead, Arvo proper passes the card off to one of
98its vanes, which each present an interface to clients for a particular
100its vanes, which each present an interface to clients for a particular
99well-defined, stable, and general-purpose piece of functionality.
101well-defined, stable, and general-purpose piece of functionality.
101As of this writing, we have seven vanes, which each provide the
103As of this writing, we have seven vanes, which each provide the
102following services:
104following services:
104−- `%ames` name of both our network and the vane that communicates over
106+- `%ames`: the name of both our network and the vane that communicates over
106−- `%behn` a simple timer
108+- `%behn`: a simple timer.
107−- `%clay` version-controlled, referentially- transparent, and global
109+- `%clay`: our version-controlled, referentially- transparent, and global
108− filesystem
110+ filesystem.
109−- `%dill` terminal driver. Unix sends keyboard events to `%dill` from
111+- `%dill`: a terminal driver. Unix sends keyboard events to `%dill` from
110 either the console or telnet, and `%dill` produces terminal output.
112 either the console or telnet, and `%dill` produces terminal output.
111−- `%eyre` http server. Unix sends http messages to `%eyre`, and
113+- `%eyre`: an http server. Unix sends http messages to `%eyre`, and
112− `%eyre` produces http messages in response
114+ `%eyre` produces http messages in response.
113−- `%ford` handles resources and publishing
115+- `%ford`: handles resources and publishing.
114−- `%gall` manages our userspace applications. `%gall` keeps state and
116+- `%gall`: manages our userspace applications. `%gall` keeps state and
115− manages subscribers
117+ manages subscribers.
120Cards are the vane-specific portion of a move. Each vane defines a
122Cards are the vane-specific portion of a move. Each vane defines a
121−protocol for interacting with other vanes (via arvo) by defining four
123+protocol for interacting with other vanes (via Arvo) by defining four
122types of cards: kisses, gifts, notes, and signs.
124types of cards: kisses, gifts, notes, and signs.
124−When one vane is `%pass`ed a card in its `++kiss`, arvo activates the
126+When one vane is `%pass`ed a card in its `++kiss`, Arvo activates the
125`++call` gate with the card as its argument. To produce a result, the
127`++call` gate with the card as its argument. To produce a result, the
126vane `%give`s one of the cards defined in its `++gift`. If the vane
128vane `%give`s one of the cards defined in its `++gift`. If the vane
127needs to request something of another vane, it `%pass`es it a `++note`
129needs to request something of another vane, it `%pass`es it a `++note`
128−card. When that other vane returns a result, arvo activates the `++take`
130+card. When that other vane returns a result, Arvo activates the `++take`
129gate of the initial vane with one of the cards defined in its `++sign`.
131gate of the initial vane with one of the cards defined in its `++sign`.
131In other words, there are only four ways of seeing a move: (1) as a
133In other words, there are only four ways of seeing a move: (1) as a
@@ -134,12 +136,12 @@ seen by the callee, a `++kiss`. (3) the response to that first request
134as seen by the callee, a `++gift`. (4) the response to the first request
136as seen by the callee, a `++gift`. (4) the response to the first request
135as seen by the caller, a `++sign`.
137as seen by the caller, a `++sign`.
137−When a `++kiss` card is passed to a vane, arvo calls its `++call` gate,
139+When a `++kiss` card is passed to a vane, Arvo calls its `++call` gate,
138passing it both the card and its duct. This gate must be defined in
140passing it both the card and its duct. This gate must be defined in
139every vane. It produces two things in the following order: a list of
141every vane. It produces two things in the following order: a list of
140−moves and a possibly-modified copy of its context. The moves are used to
142+moves and a possibly modified copy of its context. The moves are used to
141interact with other vanes, while the new context allows the vane to save
143interact with other vanes, while the new context allows the vane to save
142−its state. The next time arvo activates the vane it will have this
144+its state. The next time Arvo activates the vane it will have this
143context as its subject.
145context as its subject.
145This overview has detailed how to pass a card to a particular vane. To
147This overview has detailed how to pass a card to a particular vane. To