That's basically all you need to know to write threads. The best way to get a good handle on them is just to experiment with some strandio functions. For information on running threads from gall agents, see here and for some examples see here.

Now here's a quick recap of the main points covered:


  • is the gall agent that manages threads.
  • Details of interacting with threads via spider can be seen here.


  • are like transient gall agents
  • are used mostly to chain a series of IO operations
  • can be used by gall agents to spin out IO operations
  • live in the ted directory
  • are managed by the gall agent spider
  • take a vase and produce a strand which produces a vase


/- spider
=, strand=strand:spider
^- thread:spider
|= arg=vase
=/ m (strand ,vase)
^- form:m
(pure:m arg)


  • are the building blocks of threads
  • take this input and produce this output.
  • must be specialised to produce a particular type like (strand ,@ud).
  • are conventionally given the face m.
  • are a core that has three main arms - form, pure and bind:


  • is the mold of the strand suitable for casting
  • is the type returned by the other arms


  • simply returns the form of a strand that produces pure's argument without doing any IO


  • is used to chain strands together like javascript promises
  • is used in conjunction with micgal (;<)
  • must be specialised to a type like ;< <type> bind:m ...
  • takes two arguments. The first is a function that returns the form of a strand that produces <type>. The second is a gate whose sample is <type> and which returns a form.
  • calls the first and then, if it succeeded, calls the second with the result of the first as its sample.

Strand input

  • looks like [=bowl in=(unit input)]
  • bowl has things like our, now, eny and so forth
  • bowl is populated once when the thread is first called and then every time it receives new input
  • input contains any incoming pokes, signs and watches.

Strand output

  • contains [cards=(list card:agent:gall) <response>]
  • cards are any cards to be sent immediately
  • <response> is something like [%done value], [%fail err], etc.
  • %done will contain the result
  • responses are only used internally to manage the flow of the thread and are not returned to subscribers.


  • is located in /lib/strandio/hoon
  • contains a collection of ready-made functions for use in threads
  • eg. sleep, get-bowl, take-watch, poke, fetch-json, etc.