Transaction apps

app/example-tapp-fetch.hoon

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+::  Little app to demonstrate the structure of programs written with the
+::  transaction monad.
+::
+::  Fetches the top comment of each of the top 10 stories from Hacker News
+::
+/+  tapp, stdio
+::
+::  Preamble
+::
+=>
+  |%
+  +$  state
+    $:  top-comments=(list tape)
+    ==
+  +$  in-poke-data   [%noun =cord]
+  +$  out-poke-data  ~
+  +$  in-peer-data   ~
+  +$  out-peer-data
+    $%  [%comments (list tape)]
+    ==
+  ++  tapp   (^tapp state in-poke-data out-poke-data in-peer-data out-peer-data)
+  ++  stdio  (^stdio out-poke-data out-peer-data)
+  --
+=>
+  |%
+  ::  Helper function to print a comment
+  ::
+  ++  comment-to-tang
+    |=  =tape
+    ^-  tang
+    %+  welp
+      %+  turn  (rip 10 (crip tape))
+      |=  line=cord
+      leaf+(trip line)
+    [leaf+""]~
+  ::
+  ::  All the URLs we fetch from
+  ::
+  ++  urls
+    =/  base  "https://hacker-news.firebaseio.com/v0/"
+    :*  top-stories=(weld base "topstories.json")
+        item=|=(item=@ud `tape`:(welp base "item/" +>:(scow %ui item) ".json"))
+    ==
+  --
+=,  trad=trad:tapp
+=,  tapp-trad=tapp-trad:tapp
+=,  stdio
+::
+::  The app
+::
+%-  create-tapp-poke-peer-take:tapp
+^-  tapp-core-poke-peer-take:tapp
+|_  [=bowl:gall state]
+::
+::  Main function
+::
+++  handle-poke
+  |=  =in-poke-data
+  =/  m  tapp-trad
+  ^-  form:m
+  ::
+  ::  If requested to print, just print what we have in our state
+  ::
+  ?:  =(cord.in-poke-data 'print')
+    ~&  'drumroll please...'
+    ;<  now=@da  bind:m  get-time
+    ;<  ~        bind:m  (wait (add now ~s3))
+    ~&  'Top comments:'
+    %-  (slog (zing (turn top-comments comment-to-tang)))
+    (pure:m top-comments)
+  ?:  =(cord.in-poke-data 'poll')
+    ;<  ~  bind:m  (wait-effect (add now.bowl ~s15))
+    (pure:m top-comments)
+  ::
+  ::  Otherwise, fetch the top HN stories
+  ::
+  =.  top-comments  ~
+  ::
+  ::  If this whole thing takes more than 15 seconds, cancel it
+  ::
+  %+  (set-timeout _top-comments)  (add now.bowl ~s15)
+  ;<  =top-stories=json  bind:m  (fetch-json top-stories:urls)
+  =/  top-stories=(list @ud)
+    ((ar ni):dejs:format top-stories-json)
+  ::
+  ::  Loop through the first 5 stories
+  ::
+  =.  top-stories  (scag 5 top-stories)
+  |-  ^-  form:m
+  =*  loop  $
+  ::
+  ::  If done, tell subscribers and print the results
+  ::
+  ?~  top-stories
+    ;<  ~  bind:m  (give-result /comments %comments top-comments)
+    (handle-poke %noun 'print')
+  ::
+  ::  Else, fetch the story info
+  ::
+  ~&  "fetching item #{+>:(scow %ui i.top-stories)}"
+  ;<  =story-info=json  bind:m  (fetch-json (item:urls i.top-stories))
+  =/  story-comments=(unit (list @ud))
+    ((ot kids+(ar ni) ~):dejs-soft:format story-info-json)
+  ::
+  ::  If no comments, say so
+  ::
+  ?:  |(?=(~ story-comments) ?=(~ u.story-comments))
+    =.  top-comments  ["<no top comment>" top-comments]
+    loop(top-stories t.top-stories)
+  ::
+  ::  Else, fetch comment info
+  ::
+  ;<  =comment-info=json  bind:m  (fetch-json (item:urls i.u.story-comments))
+  =/  comment-text=(unit tape)
+    ((ot text+sa ~):dejs-soft:format comment-info-json)
+  ::
+  ::  If no text (eg comment deleted), record that
+  ::
+  ?~  comment-text
+    =.  top-comments  ["<top comment has no text>" top-comments]
+    loop(top-stories t.top-stories)
+  ::
+  ::  Else, add text to state
+  ::
+  =.  top-comments  [u.comment-text top-comments]
+  loop(top-stories t.top-stories)
+::
+++  handle-peer
+  |=  =path
+  =/  m  tapp-trad
+  ^-  form:m
+  ~&  [%tapp-fetch-take-peer path]
+  (pure:m top-comments)
+::
+++  handle-take
+  |=  sign:tapp
+  =/  m  tapp-trad
+  ^-  form:m
+  ;<  =state  bind:m  (handle-poke %noun 'fetch')
+  =.  top-comments  state
+  (pure:m top-comments)
+--

app/example-tapp-subscribe.hoon

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+/+  tapp, stdio
+=>
+  |%
+  +$  subscription-state
+    $:  target=[her=ship app=term]
+        =path
+    ==
+  +$  state
+    $:  subscription=(unit subscription-state)
+    ==
+  +$  in-poke-data   [%noun =cord]
+  +$  out-poke-data  [%noun =cord]
+  +$  out-peer-data  ~
+  +$  in-peer-data
+    $%  [%comments comments=(list tape)]
+    ==
+  ++  tapp   (^tapp state in-poke-data out-poke-data in-peer-data out-peer-data)
+  ++  stdio  (^stdio out-poke-data out-peer-data)
+  --
+=,  trad=trad:tapp
+=,  tapp-trad=tapp-trad:tapp
+=,  stdio
+%-  create-tapp-poke-diff:tapp
+^-  tapp-core-poke-diff:tapp
+|_  [=bowl:gall state]
+++  handle-poke
+  |=  =in-poke-data
+  =/  m  tapp-trad
+  ^-  form:m
+  ?:  =(cord.in-poke-data 'pull')
+    ?~  subscription
+      (trad-fail %no-subscription ~)
+    ;<  ~  bind:m  (pull-app [target path]:u.subscription)
+    (pure:m ~)
+  =/  target  [our.bowl %example-tapp-fetch]
+  ;<  ~  bind:m  (poke-app target %noun 'print')
+  ;<  ~  bind:m  (peer-app target /comments)
+  =.  subscription  `[target /comments]
+  ;<  ~  bind:m  (wait (add now.bowl ~s3))
+  (pure:m subscription)
+::
+++  handle-diff
+  |=  [[her=ship app=term] =path data=in-peer-data]
+  =/  m  tapp-trad
+  ^-  form:m
+  ?>  ?=(%comments -.data)
+  ~&  subscriber-got-data=(lent comments.data)
+  (pure:m subscription)
+--