Having looked at
pure, we'll now look at the last
bind. Bind is typically used in combination with micgal (
Micgal takes four arguments like
spec hoon hoon hoon. Given
;< a b c d, it composes them like
((b ,a) c |=(a d)). So, for example, these two expressions are equivalent:
;< ~ bind:m (sleep:strandio ~s2)(pure:m !>(~))
((bind:m ,~) (sleep:strandio ~s2) |=(~ (pure:m !>(~))))
Micgal exists simply for readability. The above isn't too bad, but consider this:
;< a b c;< d e f;< g h ij
...as opposed to this monstrosity:
((b ,a) c |=(a ((e ,d) f |=(d ((h ,g) i |=(g j))))))
Bind by itself must be specialised like
(bind:m ,<type>) and it takes two arguments:
- The first argument is a function that returns the
formof a strand which produces
- The second argument is a gate whose sample is
<type>and which returns a
Since you'll invariably use it in conjunction with micgal, the
;< <type> bind:m ... will both specialise
bind and specify the gate's sample.
Bind calls the first function then, if it succeeded, calls the second gate with the result of the first as its sample. If the first function failed, it will instead just return an error message and not bother calling the next gate. So it's essentially "strand A then strand B".
Since the second gate may itself contain another
;< <type> bind:m ..., you can see how this allows you to glue together an arbitrarily large pipeline, where subsequent gates depend on the previous ones.
/lib/strandio/hoon contains a large collection of useful, ready-made functions for use in threads. For example:
sleepwaits for the specified time.
get-timegets the current time.
pokepokes an agent.
watchsubscribes to an agent.
fetch-jsonproduces the JSON at a particular URL.
retrytries a strand repeatedly with exponential backoff until it succeeds.
start-threadstarts another thread.
send-raw-cardsends any card.
...and many more.
Putting it together
Here's a simple thread with a couple of
/- spider/+ strandio=, strand=strand:spider^- thread:spider|= arg=vase=/ m (strand ,vase)^- form:m;< t=@da bind:m get-time:strandio;< s=ship bind:m get-our:strandio(pure:m !>([s t]))
Save it as
|commit it and run it with
-mythread. You should see something like:
> -mythread[~zod ~2021.3.8..14.52.15..bdfe]
strandio functions we've imported the library with
get-our get the current time & ship from the bowl in
strand-input. We'll discuss
strand-input in more detail later.
Note how we've specified the face and return type of each strand like
You can see how
pure has access to the results of previous strands in the pipeline. Note how we've wrapped
pure's argument in a
!> because the thread must produce a
Next we'll look at
strand-input in more detail.