. dot · Nock

Anything Nock can do, Hoon can do also. These runes are used for carrying out Nock operations in Hoon.

.^ "dotket"

Load from the Arvo namespace (scry) with a fake Nock instruction: Nock 12.

Syntax

Two arguments, with the second optionally split into an arbitrary number of elements.

While this rune technically takes a fixed number of arguments, q is usually split into at least two parts, and the tall form of this rune must be terminated with a ==. Note also that the == does not make the arguments into a list as you might expect, so q must be explicitly null-terminated if its elements are specified separately.

.^  p
  q1
  q2
  q3
  qn
==

.^(p q1 q2)

AST

[%dtkt p=spec q=hoon]

Produces

The noun q, cast to the type p.

Discussion

Nock has no 12 instruction! But the virtual Nock used to run userspace code does. Nock 12 loads from a typed immutable namespace defined by its virtual context.

Ordinarily a Hoon expression has access to no information but whatever can be found in the subject. The one exception is with the .^ rune. It essentially allows you to request information from one of the Arvo vanes (modules).

.^ checks that the type of the value retrieved from Arvo nests under p. q is a path which includes information about which vane is being queried, and what sort of information is requested.

In principle .^ takes two subexpressions, but in practice q is often given in two parts: the first part includes the vane to be queried (e.g., %a for Ames, %b for Behn, %c for Clay, etc.) and the kind of request. The second part is a path that corresponds to the kind of request.

Examples

In the dojo we can ask Clay -- the Arvo filesystem -- for a listing of the files at our current path, %:

> .^(arch %cy %)
[ fil=~
    dir
  { [p=~.app q=~]
    [p=~.sur q=~]
    [p=~.gen q=~]
    [p=~.lib q=~]
    [p=~.mar q=~]
    [p=~.ted q=~]
    [p=~.desk q=~]
    [p=~.sys q=~]
  }
]

The %c is for Clay, and the y is for the request type. arch is the type of the listing. See gen/cat.hoon to see how this information is printed more prettily.

The % is for the current path in the dojo:

> `path`%
/~zod/base/~2018.9.20..23.05.35..0231

You can modify the time of the file listing quite simply and ask for a listing from 5 hours ago. (Remember that Clay is a revision-controlled file system.)

> .^(arch %cy /(scot %p our)/base/(scot %da (sub now ~h5)))
[ fil=~
    dir
  { [p=~.app q=~]
    [p=~.sur q=~]
    [p=~.gen q=~]
    [p=~.lib q=~]
    [p=~.mar q=~]
    [p=~.ted q=~]
    [p=~.desk q=~]
    [p=~.sys q=~]
  }
]

our is the value for your ship's name.

.+ "dotlus"

Increment an atom with Nock 4.

Syntax

One argument, fixed.

.+  p

.+(p)

  +(p)

AST

[%dtls p=hoon]

Produces

p plus 1 if p is an atom; otherwise, crashes. The product atom has no aura.

Examples

> .+(6)
7

> +(6)
7

> +(%foo)
7.303.015

> +([1 2])
nest-fail

.* "dottar"

Evaluate with Nock 2.

Produces

Nock of formula q and subject p, with type %noun.

Syntax

Two arguments, fixed.

.*  p
q

.*(p q)

AST

[%dttr p=hoon q=hoon]

Discussion

.*(p q) is used to run Nock formula q on the subject p from within Hoon.

Keep in mind that p and q can be arbitrary Hoon expressions, as long as they evaluate to the appropriate nouns for Nock evaluation.

Note also that .* ("dottar") can be used to bypass the type system. It's therefore possible to use Hoon as a typeless language.

Examples

> .*([20 30] [0 2])
20

> .*(33 [4 0 1])
34

> .*(|.(50) [9 2 0 1])
50

> .*(12 [7 [`1 [4 `1]] [`2 `3 `2]])
[12 13 12]

> .*(~ [5 1^4 [4 1^3]])
0

> .*(~ [5 1^5 [4 1^3]])
1

.= "dottis"

Test for equality with Nock 5.

Syntax

Two arguments, fixed.

.=  p
q

.=(p q)

  =(p q)

AST

[%dtts p=hoon q=hoon]

Produces

%.y if p equals q; otherwise %.n.

Discussion

Like Nock equality, .= ("dottis") tests whether two nouns are the same, ignoring invisible pointer structure. Because in a conventional noun implementation each noun has a lazy short hash, comparisons are fast unless the hash needs to be computed, or we are comparing separate copies of identical nouns. (Comparing large duplicates is a common cause of performance bugs.)

Examples

> .=(0 0)
%.y

> =(0 0)
%.y

> .=(1 2)
%.n

> =(1 2)
%.n

> =(12 [12 14])
%.n

.? "dotwut"

Test for cell or atom with Nock 3.

Syntax

One argument, fixed.

.?  p

.?(p)

AST

[%dtwt p=hoon]

Produces

%.y if p is a cell; otherwise %.n.

Examples

> .?(42)
%.n

> .?([42 43])
%.y