!, "zapcom"

Produce the Hoon AST of an expression.

Syntax

Two arguments, fixed.

!,  p
q

!,(p q)

AST

[%zpcm p=hoon q=hoon]

Discussion

This produces the $hoon AST of expression q. The first argument, p, is always an example of the $hoon type, typically just the *hoon bunt value, and is used for type inference. The reason for p is just to handle transitions if the $hoon type changes.

Examples

> !,  *hoon  [1 1]
[%cltr p=~[[%sand p=%ud q=1] [%sand p=%ud q=1]]]

> !,  *hoon  (add 1 1)
[%cncl p=[%wing p=~[%add]] q=~[[%sand p=%ud q=1] [%sand p=%ud q=1]]]

!> "zapgar"

Wrap a noun in its type (form a vase).

Syntax

One argument, fixed.

!>  p

!>(p)

AST

[%zpgr p=hoon]

Produces

A cell whose tail is the product of p, and whose head is the static type of p.

Discussion

In Hoon, a dynamic type is a static type compiled at runtime. This type-noun cell is generally called a vase.

Examples

> !>(1)
[#t/@ud q=1]

If you want just the type value, use a 'type spear'. This is -:!>, i.e., the head of the cell produced by !>:

> -:!>(1)
#t/@ud

!< "zapgal"

Extracts a vase to the given mold if its type nests.

Syntax

Two arguments, fixed.

!<  p
q

!<(p q)

AST

[%zpgl p=spec q=hoon]

Produces

The value of vase q typed with the type of mold p if possible, else a nest-fail.

Discussion

This is something like a partial inverse to the !> rune and can be used to extract a typed value from a vase.

Examples

> !<  @  !>  ~zod
0

> !<  @p  !>  0
nest-fail

> !<  tape  !>("foobar")
"foobar"

!; "zapmic"

Wrap a noun in its type (raw).

Syntax

Two arguments, fixed.

!;  p
q

!;(p q)

AST

[%zpmc p=hoon q=hoon]

Discussion

This wraps the product of q in its inferred type. It's a raw version of !>. Unlike zapgar, q is not given a p face and its type information is not stripped to a raw noun.

The first field, p, must be an example of the $type type, typically just *type (the bunt of $type). The p argument is just so transitions can be handled if the $type type changes.

It's unlikely you'd use this rune directly; !> is much more typical.

Examples

> !;  *type  [1 1]
[#t/[@ud @ud] 1 1]

> !;  *type  'foo'
[#t/@t 'foo']

!= "zaptis"

Make the Nock formula for a Hoon expression.

Syntax

One argument, fixed.

!=  p

!=(p)

AST

[%zpts p=hoon]

Produces

The Nock generated by p.

Discussion

Don't confuse != with a negation, !, followed by a test for equality, =(10 11).

Examples

> !=(20)
[1 20]

> !=(~zod)
[1 0]

> !=((add 2 2))
[8 [9 3.110.356 0 31] 9 2 [0 4] [7 [0 3] 1 2 2] 0 11]

Don't confuse the != rune with:

> !=(10 11)
%.y

> !=(10 10)
%.n

The syntax difference is that a test for equality takes two subexpressions, and the != rune only one.

!? "zapwut"

Restrict Hoon version.

Syntax

Two arguments, fixed.

!?  p
q

!?(p q)

AST

[%zpwt p=$@(p=@ [p=@ q=@]) q=hoon]

Produces

When p is an atom:

• q if p ≥ Hoon kelvin version, otherwise crash.

When p is a cell:

• q, if p.p ≥ Hoon kelvin version ≥ q.p, otherwise crash.

(Versions count down; the current version is 140.)

Examples

> !?  [142 140]  (add 2 2)
4

> !?  142  (add 2 2)
4

> !?  64  (add 2 2)
! exit

!@ "zappat"

Branch on whether a wing exists.

Syntax

Three arguments, fixed.

!@  p
  q
r

!@(p q r)

AST

[%zppt p=(list wing) q=hoon r=hoon]

Discussion

p is a wing reference like foo, bar.foo, etc. If p exists, q. If p does not exist, r. Essentially, this is like ?: for wing existence.

Examples

> =foo 42

> !@(foo 'exists' 'does not exist')
'exists'

> !@(baz 'exists' 'does not exist')
'does not exist'

!! "zapzap"

Crash.

Syntax

No arguments.

!!

!!

AST

[%zpzp ~]

Produces

Nothing. Always crashes, with type %void.

Discussion

%void nests in every other type, so you can stub out anything with !!.

Examples

> !!
dojo: hoon expression failed

!: "zapcol"

Turn on stack trace.

Syntax

One argument, fixed

!:  p

!:(p)

Produces

The product of p unless p crashes, in which case a stack trace is given.

Discussion

!: is used to turn on a debugging stack trace option for any code you have in p.

Examples

> ?:(=(0 1) 123 !!)
dojo: hoon expression failed

> !:  ?:(=(0 1) 123 !!)
/~zod/base/~2022.4.2..08.54.53..07d7:<[1 5].[1 22]>
/~zod/base/~2022.4.2..08.54.53..07d7:<[1 19].[1 21]>
dojo: hoon expression failed

!. "zapdot"

Turn off stack trace for a subexpression p

Syntax

One argument, fixed.

!.  p

!.(p)

Produces

The product of p. If p crashes, no stack trace entries are given for that code.

Discussion

!. is used to turn off a debugging stack trace option for any code you have in p. This rune can be embedded under a !: rune for inner loops of your code that you don't want or need to trace. This is especially useful if a trace overflows the stack.

Examples

> %.(1 |=(a=@ ^-(@ ?:(=(a 10) !! $(a +(a))))))
dojo: hoon expression failed

> !:  %.(1 |=(a=@ ^-(@ ?:(=(a 10) !! $(a +(a))))))
/~zod/base/~2022.4.2..08.56.45..5ecc:<[1 5].[1 49]>
/~zod/base/~2022.4.2..08.56.45..5ecc:<[1 17].[1 47]>
/~zod/base/~2022.4.2..08.56.45..5ecc:<[1 22].[1 46]>
...skipping some lines...
/~zod/base/~2022.4.2..08.56.45..5ecc:<[1 22].[1 46]>
/~zod/base/~2022.4.2..08.56.45..5ecc:<[1 33].[1 35]>
dojo: hoon expression failed

> !:  %.(1 !.(|=(a=@ ^-(@ ?:(=(a 10) !! $(a +(a)))))))
/~zod/base/~2022.4.2..08.57.07..d40b:<[1 5].[1 53]>
dojo: hoon expression failed