@@ -11,70 +11,73 @@ Network messages
1111Now we've learned enough Hoon to do more interesting things. Let's get
1212our planets to talk to each other.
1313
14−All we've written up until now are just shell commands that produce a
15−value and then disappear. To listen for and receive messages from other
16−planets, we'll need an app. Let's look at a very simple one:
14+All we've written up until now are just shell commands that produce a value and
15+then disappear. To listen for and receive messages from other planets, we'll
16+need an app. Let's look at a very simple one, `echo.hoon`:
1717
1818 :: Accepts any noun from dojo and prints it out
1919 ::
20− :::: /hoon/echo/examples/app
20+ :::: /===/app/echo/hoon
2121 ::
22− /? 314
23− !:
24− |_ {bowl state/$~}
25− ++ poke-noun
26− |= arg/*
27− ^- {(list) _+>.$}
28− ~& [%argument arg]
29− [~ +>.$]
30− --
22+ !: :: enables debug printfs
23+ |% :: forms a core with subject as payload
24+ ++ move {bone card} :: defines echo app's arvo move mold
25+ ++ card $% $~ :: defines card (data) mold as null tagged union
26+ == :: end of mold definition; see $%
27+ -- :: end of card arm definition
28+ :: ::
29+ |_ {bow/bowl $~} :: forms a core with bowl (app state) as sample
30+ ++ poke-noun :: begin definition of poke-noun arm
31+ |= non/* :: forms a gate which accepts any noun
32+ ^- {(list move) _+>.$} :: casts product to mold of moves and context
33+ ~& echo+noun+non :: debug printf, i.e. '[%echo %noun *]'
34+ [~ +>.$] :: produce a cell of empty list and our state
35+ -- :: end of poke-noun arm definition
3136
3237This is a very simple app that does only one thing. If you poke it with
3338a value, it prints that value out. To try this out, you have to start
3439the app, then you can poke it from the command line with the following
3540commands:
3641
37− ~fintud-macrep:dojo> |start %examples-echo
38− 'prep'
42+ ~fintud-macrep:dojo> |start %echo
3943 >=
40− ~fintud-macrep:dojo> :examples-echo 5
41− [%argument 5]
44+ ~fintud-macrep:dojo> :echo 5
45+ [%echo %noun 5]
4246 >=
4347 ~fintud-macrep:dojo> :examples-echo [1 2]
44− [%argument [1 2]]
48+ [%echo %noun [1 2]]
4549 >=
4650
47−> There is currently a bug where the `%argument` lines are printed
48−> *above* the line you entered, so your output may not look exactly like
49−> this. `>=` means that a command was successfully received and
50−> executed.
51+> There is currently a bug where the `[%echo %noun *]` lines are printed *above*
52+> the line you entered, so your output may not look exactly like this. `>=`
53+> means that a command was successfully received and executed.
5154
5255Most of the app code should be simple enough to guess its function. The
5356important part of this code is the definition of `++poke-noun`.
5457
55−Once an app starts, it's always running in the background and you
56−interact with it by sending it messages. The most straightforward way to
57−do that is to poke it from the command line, which we we did with
58−`:echo 5` (`:[app-name] [argument(s)]`).
58+Once an app starts, it's always running in the background and you interact with
59+it by sending it messages. The most straightforward way to do that is to poke it
60+from the command line, which we we did with `:echo 5`
61+(`:[app-name] [argument(s)]`).
5962
60−In this case, `++poke-noun` takes an argument `arg` and prints it out
61−with `~&` ([sigpam](../../hoon/twig/sig-hint/pam-dump/)). This is an unusual
62−rune that formally "does nothing", but the interpreter detects it and
63−printfs the first child, before executing the second as if the first
64−didn't exist. This is a slightly hacky way of printing to the console,
63+In this case, `++poke-noun` takes an argument (*sample*) `arg` and
64+prints it to dojo with `~&` ([sigpam](../../hoon/twig/sig-hint/pam-dump/)).
65+This is an unusual rune that formally "does nothing", but the interpreter
66+detects it and printfs the first child, before executing the second as if the
67+first didn't exist. This is a slightly hacky way of printing to the console,
6568but we'll get to the correct way later on.
6669
67−But what does `++poke-noun` produce? Recall that `^-` casts to a type.
68−In this case, it's declaring that the end result of the function will be of
69−type `{(list) _+>.$}`. But what does this mean?
70+But what does `++poke-noun` produce? Recall that `^-` casts to a type. In this
71+case, it's declaring that the end result (*product*) of the function
72+(`++poke-noun`'s *gate*) will be of type `{(list) _+>.$}`. But what does this
73+mean?
7074
71−The phrase to remember is "a list of moves and our state". Urbit is a
72−message passing system, so whenever we want to do something that
73−interacts with the rest of the system, we send a message. Thus, a move
74−is Arvo's equivalent of a syscall. The first thing that `++poke-noun`
75−produces is a list of messages, called "moves". In this case, we don't
76−actually want the system to do anything, so we produce the empty list,
77−`~` (in the `[~ +>.$]` line).
75+The phrase to remember is "a list of moves and our state". Urbit is a message
76+passing system, so whenever we want to do something that interacts with the rest
77+of the system, we send a message. Thus, a move is Arvo's equivalent of a
78+syscall. The first thing that `++poke-noun` produces is a list of messages,
79+called "moves". In this case, we don't actually want the system to do anything,
80+so we produce the empty list, `~` (in the `[~ +>.$]` line).
7881
7982The second thing `++poke-noun` produces is our state. `+>.$` refers to a
8083particular address in our subject where our formal app state is stored.
@@ -85,21 +88,28 @@ Let's look at another example (edit your code in
8588`/app/examples/echo/hoon` to reflect the code below). Say we want to
8689only accept a number, and then print out the square of that number.
8790
88− /? 314
89− !:
90− |_ {bowl state/$~}
91+ :: Accepts an atom from the dojo and squares it.
9192 ::
93+ :::: /===/app/square/hoon
94+ ::
95+ !:
96+ |% ::> no moves in :square
97+ ++ move {bone card} ::> no cards in :square
98+ ++ card $% $~
99+ ==
100+ --
101+ :: ::< stateless
102+ |_ {bow/bowl $~}
92103 ++ poke-atom
93− |= arg/@
94− ^- {(list) _+>.$}
95− ~& [%square (mul arg arg)]
96− [~ +>.$]
97− --
104+ |= tom/@
105+ ^- {(list move) _+>.$}
106+ ~& square+(mul tom tom)
107+ [~ +>.$]
108+ --
98109
99−A few things have changed. Firstly, we no longer accept arbitrary nouns
100−because we can only square atoms (integers, in this case an unsigned
101−one). Thus, our argument is now `arg/@`. Secondly, it's `++poke-atom`
102−rather than `++poke-noun`.
110+A few things have changed. Firstly, we no longer accept arbitrary nouns because
111+we can only square atoms (integers, in this case an unsigned one). Thus, our
112+argument is now `tom/@`. Secondly, it's `++poke-atom` rather than `++poke-noun`.
103113
104114Intro to marks
105115==============
@@ -124,9 +134,9 @@ using `&[mark]`. Try the following commands:
124134
125135 ~fintud-macrep:dojo> |start %square
126136 >=
127− ~fintud-macrep:dojo> :examples-square 6
137+ ~fintud-macrep:dojo> :square 6
128138 gall: %square: no poke arm for noun
129− ~fintud-macrep:dojo> :examples-square &atom 6
139+ ~fintud-macrep:dojo> :square &atom 6
130140 [%square 36]
131141 >=
132142
@@ -143,68 +153,79 @@ so we'll be getting quite used to them.
143153Sending a message to another urbit
144154==================================
145155
146−Let's write our first network message! Here's `/app/examples/pong.hoon`:
156+Let's write our first network message! Here's `examples/app/pong.hoon`:
147157
148− /? 314
158+ :: Allows one urbit to send the string 'Pong' to
159+ :: another urbit.
160+ ::
161+ :::: /===/app/pong/hoon
162+ ::
163+ !:
149164 |%
150− ++ move {bone term wire *}
165+ ++ move {bone card}
166+ ++ card $% {$poke wire dock poke-contents}
167+ ==
168+ ++ poke-contents $% {$atom @}
169+ ==
151170 --
152− !:
153− |_ {bowl state/$~}
171+ |_ {bow/bowl $~} ::< stateless
154172 ::
155173 ++ poke-urbit
156− |= to/@p
174+ |= to/ship
157175 ^- {(list move) _+>.$}
158− [[[ost %poke /sending [to dap] %atom 'howdy'] ~] +>.$]
176+ ~& pong+'Outgoing pong!'
177+ :_ +>.$
178+ ~[[ost.bow %poke /sending [to dap.bow] %atom 'Pong']]
159179 ::
160180 ++ poke-atom
161− |= arg/@
181+ |= tom/@
162182 ^- {(list move) _+>.$}
163− ~& [%receiving (@t arg)]
183+ ~& pong+'Incoming pong!'
184+ ~& pong+received+`@t`tom
164185 [~ +>.$]
165186 ::
166187 ++ coup |=(* [~ +>.$])
188+ ::
167189 --
168−
190+
169191Run it with these commands:
170192
171− ~fintud-macrep:dojo> |start %examples-pong
193+ ~fintud-macrep:dojo> |start %pong
172194 >=
173− ~fintud-macrep:dojo> :examples-pong &urbit ~sampel-sipnym
195+ ~fintud-macrep:dojo> :pong &urbit ~sampel-sipnym
174196 >=
175197
176−Replace `~sampel-sipnym` with another urbit. The easiest thing to do is
177−to start a moon, a sub-identity of your urbit. If you don't know how to
178−start a moon, see [the user admin section](/docs/using/admin/). Don't
179−forget to start the `%examples-pong` app on that urbit, too. You should
180−see, on the foreign urbit, this output:
181−
182− [%receiving 'howdy']
183−
184−Most of the code should be straightforward. In `++poke-atom`, the only
185−new thing is the expression `(@t arg)`, which is the type `@t` being
186−called as a function with argument `arg`. As we already know, `@t` is
187−the type of "cord" text strings. In Hoon, when types are called as
188−functions, they serve as a validator function called a "clam" -- that
189−is, a function whose domain is all nouns, and range is the given type
190−(in this case, `@t`).
191−
192−In simpler terms, if a clam is passed a value of its own type, it
193−produces that value. Otherwise, it produces the default value (aka the
194−"bunt") of its type. Here we call this `@t` function on the argument.
195−This coerces the argument to text, so that we can print it out prettily
196−no matter what we're passed.
197−
198−The more interesting part is in `++poke-urbit`. The `urbit` mark is an
199−urbit identity, and the Hoon type associated with it is `@p` (the "p"
198+Replace `~sampel-sipnym` with another urbit. The easiest thing to do is to start
199+a comet, a free and disposable Urbit identity. If you don't know how to start a
200+comet, see [the user setup section](/docs/using/setup/). Don't forget to start
201+the `%pong` app on that urbit, too. You should see, on the foreign
202+urbit, this output:
203+
204+ [%pong 'Incoming pong!']
205+ [%pong %received 'Pong']
206+
207+Most of the code should be straightforward. In `++poke-atom`, the only new thing
208+is the expression `` `@t`tom ``, which is *casting* the argument `tom` to type
209+`@t`. As we already know, `@t` is the type of "cord" (text string). In Hoon,
210+another way to perform a kind of casting is to use a type as a function, like
211+this: `(@t tom)`. When types are called like this, they are called "clams",
212+and they serve as validator functions-- that is, functions whose domain is all
213+nouns, and range is the given type (in this case, `@t`). Clams will "bunt" the
214+default value of the mold whereas casts (`@t`tom) may `nest-fail` if the
215+argument passed to it does not fit. An example of such a failure case is
216+passing a cell to an atom: `` `@`[1 2] ``. Using a clam here instead
217+(`(@ [1 2])`) will bunt the default value of `@`, which is `0`. Try it in dojo!
218+
219+The more interesting part is in `++poke-urbit`. The `urbit` mark is an urbit
220+identity, and the Hoon type associated with it is `ship` or `@p` (the "p"
200221stands for "phonetic base").
201222
202−Recall that in a `++poke` arm we produce "a list of moves and our
203−state". Until now, we've left the list of moves empty, since we haven't
204−wanted to tell Arvo to do anything in particular. Now we want to send a
205−message to another urbit. Thus, we produce a list with one element:
223+Recall that in a `++poke` arm we produce "a list of moves and our state". Until
224+now, we've left the list of moves empty, since we haven't wanted to tell Arvo to
225+do anything in particular. Now we want to send a message to another urbit. Thus,
226+we produce a list with one element:
206227
207− [ost %poke /sending [to-urbit-address %pong] %atom 'howdy']
228+ ~[[ost.bow %poke /sending [to dap.bow] %atom 'Pong]]
208229
209230### Moves
210231
@@ -218,73 +239,68 @@ Let's walk through each of these elements step by step.
218239
219240#### Bones ("cause")
220241
221−If you look up `++bone` in `hoon.hoon`, you'll see that it's a number
222−(`@ud`), and that it's an opaque reference to a duct. `++duct` in
223−hoon.hoon is a list of `wire`s, where `++wire` is an alias for `++path`.
224−`++path` is a list of `++knot`s, which are ASCII text. Thus, a duct is a
225−list of paths, and a bone is an opaque reference to it (in the same way
226−that a Unix file descriptor is an opaque reference to a file structure).
227−Thus, to truly understand bones, we must understand ducts.
228−
229−A duct is stack of causes, again, represented as paths, which are called
230−wires. At the bottom of every duct is a unix event, such as a keystroke,
231−network packet, file change, or timer event. When Arvo is given this
232−event, it routes the event to appropriate kernel module for handling.
233−
234−Sometimes, the module can immediately handle the event and produce any
235−necessary results. For example, when we poked the `++poke-atom` arm
236−above, we poked %gall, our application server, which was able to respond
237−to our poke directly. When the module cannot service the request itself,
238−it sends instructions to another kernel module or application (through the
239−%gall module) to do a specified action, and produces the result from
240−that.
242+If you look up `++bone` in `hoon.hoon`, you'll see that it's a number (`@ud`),
243+and that it's an opaque reference to a duct. `++duct` in `hoon.hoon` is a list
244+of `wire`s, where `++wire` is an alias for `++path`. `++path` is a list of
245+`++knot`s, which are ASCII text. Thus, a duct is a list of paths, and a bone is
246+an opaque reference to it (in the same way that a Unix file descriptor is an
247+opaque reference to a file structure). Thus, to truly understand bones, we must
248+understand ducts.
249+
250+A duct is a stack of causes, again, represented as paths, which are called wires.
251+At the bottom of every duct is a unix event, such as a keystroke, network
252+packet, file change, or timer event. When Arvo is given this event, it routes
253+the event to appropriate kernel module for handling.
254+
255+Sometimes, the module can immediately handle the event and produce any necessary
256+results. For example, when we poked the `++poke-atom` arm above, we poked %gall,
257+our application server, which was able to respond to our poke directly. When the
258+module cannot service the request itself, it sends instructions to another
259+kernel module or application (through the %gall module) to do a specified
260+action, and produces the result from that.
241261
242262Furthermore, when one module sends a message to another kernel module or
243−application, it also sends along the duct it was given with its new wire
244−tacked onto the end. Now the duct has two entries, with the unix event on
245−the bottom and the kernel module that handled it next. This process can
246−continue indefinitely, adding more and more layers onto the duct. When
247−an entity finally produces a result, a layer is popped off the duct, and
248−the result is passed all the way back down.
249−
250−In effect, a duct is an Arvo-level call stack. It's worth noting that
251−while in traditional call stacks a function call happens synchronously
252−and returns exactly once. In Arvo, multiple moves can be sent at once,
253−are evaluated asynchronously, and each one may be responded to zero or
254−more times.
255−
256−The point to take home is that whatever caused `++poke-urbit` to be
257−called is also the root cause for the network message we're trying to
258−send. Thus, we say to send the network message along the given bone
259−`ost`.
260−
261−##### Wire ('tack on new layer to duct')
262−
263−Of course, we have to push a new layer onto our duct before passing it
264−along (or responding to it directly) anywhere. This layer can have any
265−data we want in it, but we don't need anything specific here, so we just
266−use the wire `/sending` (`/elem1/elem2/elemN` is one syntax used to
267−create `++path`s and `++wire`s of N elements). If we were expecting a
268−response (which we're not), it would come back along the `/sending`
269−wire, meaning that the path `/sending` will be passed back to the
270−response handler as an argument. Although it's not required, it's
271−generally a good idea to make the wire human-readable for bug-handling
272−purposes.
263+application, it also sends along the duct it was given with its new wire tacked
264+onto the top. Now the duct has two entries, with the unix event on the bottom
265+and the kernel module that handled it on top. This process can continue
266+indefinitely, pushing more and more wires onto the top of the duct. When an
267+entity finally produces a result, a wire is popped off the duct, and the result
268+is passed all the way back down, repeating the process of wire popping
269+sequentially until the bottom of the duct is reached.
270+
271+In effect, a duct is an Arvo-level call stack. It's worth noting that while in
272+traditional call stacks a function call happens synchronously and returns
273+exactly once. In Arvo, multiple moves can be sent at once, are evaluated
274+asynchronously, and each one may be responded to zero or more times.
275+
276+The point to take home is that whatever caused `++poke-urbit` to be called is
277+also the root cause for the network message we're trying to send. Thus, we say
278+to send the network message along the given bone `ost`.
279+
280+##### Wire (path)
281+
282+Of course, we have to push a new wire onto our duct before passing it along (or
283+responding to it directly) anywhere. This wire can have any data we want in it,
284+but we don't need anything specific here, so we just use the wire `/sending`
285+(`/elem1/elem2/elemN` is one syntax used to create `++path`s and `++wire`s of N
286+elements). If we were expecting a response (which we're not), it would come back
287+along the `/sending` wire, meaning that the path `/sending` will be passed back
288+to the response handler as an argument. Although it's not required, it's
289+generally a good idea to make the wire human-readable for bug-handling purposes.
273290
274291##### Term (sys-call)
275292
276−Each move also has a `term`, composed of lowercase ASCII and/or `-`.
277−This `term` has the sign `@tas`. In this case, out `term` is `%poke`,
278−which is the name of the particular kind of move we're sending. You can
279−always use `%poke` to message an app. Other common names include
280−`%warp`, to read from the filesystem; `%wait`, to set a timer; and
281−`%them`, to send an http request.
293+Each move also has a `term`, composed of lowercase ASCII and/or `-`. This `term`
294+has the sign `@tas`. In this case, our `term` is `%poke`, which is the name of
295+the particular kind of move we're sending. You can always use `%poke` to message
296+an app. Other common names include `%warp`, to read from the filesystem;
297+`%wait`, to set a timer; and `%them`, to send an http request.
282298
283299The move ends with `*` (that is, any noun) since each type of move takes
284−different data. In our case, a `%poke` move takes a target (urbit and
285−app) and marked data, then pokes the arm of the corresponding mark on
286−that app on that urbit with that data. `[to-urbit-address %pong]` is the
287−target urbit and app, `%atom` is the `mark`, and`'howdy'` is the data.
300+different data. In our case, a `%poke` move takes a target (urbit and app) and
301+marked data, then pokes the arm of the corresponding mark on that app on that
302+urbit with that data. `[to-urbit-address %pong]` is the target urbit and app,
303+`%atom` is the `mark`, and`'Pong'` is the data.
288304
289305When Arvo receives a `%poke` move, it calls the appropriate `++poke`.
290306The same mechanism is used for sending messages between apps on the same
@@ -300,7 +316,7 @@ urbit as for sending messages between apps on different urbits.
300316- Extend either of the apps in the first two exercises to accept input
301317 over the network in the same way as `pong`.
302318
303−- Modify `examples-pong` to print out a message when it receives
319+- Modify `pong.hoon` to print out a message when it receives
304320 acknowledgement.
305321
306322- Write two apps, `even` and `odd`. When you pass an atom to `even`,