2b: List Logic
+bake
+bakeNote: This function isn't specifically a list function but is included in section 2b of the standard library so is documented here for completeness.
Convert wet gate .f to a dry gate by specifying argument mold .a.
+bake is a wet gate that takes a wet gate and produces a dry gate.
Accepts
.f is a $gate.
.a is a $mold.
Produces
A dry $gate whose sample type is .a.
Source
++ bake
|* [f=gate a=mold]
|= arg=a
(f arg)Examples
> =wet-gate |*(a=* [a a])
> (wet-gate 42)
[42 42]
> (wet-gate ['foo' 'bar'])
[['foo' 'bar'] 'foo' 'bar']
> =dry-gate (bake wet-gate @ud)
> (dry-gate 42)
[42 42]
> (dry-gate ['foo' 'bar'])
-need.@ud
-have.[@t @t]
nest-fail+fand
+fandAll indices in +list
Produces the indices of all occurrences of .nedl in .hstk as a +list of atoms.
Accepts
.nedl is a list.
.hstk is a list.
Produces
A +list.
Source
++ fand
~/ %fand
|= [nedl=(list) hstk=(list)]
=| i=@ud
=| fnd=(list @ud)
|- ^+ fnd
=+ [n=nedl h=hstk]
|-
?: |(?=(~ n) ?=(~ h))
(flop fnd)
?: =(i.n i.h)
?~ t.n
^$(i +(i), hstk +.hstk, fnd [i fnd])
$(n t.n, h t.h)
^$(i +(i), hstk +.hstk)Examples
> (fand ~[3] ~[1 2 3])
~[2]> (fand ~[4] ~[1 2 3])
~> (fand ~['a'] "cbabab")
~[2 4]> (fand "ba" "cbabab")
~[1 3]+find
+findFirst index in +list
Produces the index of the first occurrence of .nedl in .hstk as the +unit of an atom.
Accepts
.nedl is a list.
.hstk is a list.
Produces
The +unit of an atom.
Source
++ find
~/ %find
|= [nedl=(list) hstk=(list)]
=| i=@ud
|- ^- (unit @ud)
=+ [n=nedl h=hstk]
|-
?: |(?=(~ n) ?=(~ h))
~
?: =(i.n i.h)
?~ t.n
`i
$(n t.n, h t.h)
^$(i +(i), hstk +.hstk)Examples
> (find [3]~ ~[1 2 3])
[~ u=2]> (find [4]~ ~[1 2 3])
~> (find ['c']~ "cbabab")
[~ u=0]> (find "ab" "cbabab")
[~ u=2]> (find "bab" "cbabab")
[~ u=1]+flop
+flopReverse
Produces the +list .a in reverse order.
Accepts
.a is a +list.
Produces
A +list.
Source
++ flop
~/ %flop
|* a=(list)
=> .(a (homo a))
^+ a
=+ b=`_a`~
|-
?~ a b
$(a t.a, b [i.a b])Examples
> =a [1 2 3 ~]
> (flop a)
~[3 2 1]> (flop (flop a))
~[1 2 3]+gulf
+gulfList from range
Produces a +list composed of each consecutive integer starting from .a and ending with .b. .a and .b are themselves included.
Accepts
.a is an atom.
.b is an atom.
Produces
a +list.
Source
++ gulf
|= [a=@ b=@]
?> (lte a b)
|- ^- (list @)
?:(=(a +(b)) ~ [a $(a +(a))])Examples
> (gulf 1 6)
~[1 2 3 4 5 6]> `(list @t)`(gulf 99 106)
<|c d e f g h i j|>+homo
+homoHomogenize
Produces a +list whose type is a fork of all the contained types in the list .a. Used when you want to make all the types of the elements of a list the same.
Accepts
.a is a +list.
Produces
a +list.
Source
++ homo
|* a=(list)
^+ =< $
|@ ++ $ ?:(*? ~ [i=(snag 0 a) t=$])
--
aExamples
> lyst
[i=1 t=[i=97 t=[i=2 t=[i=98 t=[i=[~ u=10] t=~]]]]]
> (homo lyst)
~[1 97 2 98 [~ u=10]]> =a (limo [1 2 3 ~])
> a
[i=1 t=[i=2 t=[i=3 t=~]]]
> (homo a)
~[1 2 3]+into
+intoInsert item at index
Accepts a +list .a, an atom .b, and a noun .c, producing the list of .a with the item .c inserted at index .b.
Accepts
.a is a list.
.b is a atom.
.c is a noun.
Produces
the list of .a with the item .c inserted at index .b.
Source
++ into
~/ %into
|* [a=(list) b=@ c=*]
^+ a
(weld (scag b a) [c (slag b a)])Examples
> (into (limo ~[2 3 4]) 1 11)
~[2 11 3 4]+join
+joinConstructs a new +list, placing sep between every element of lit.
Accepts
sep is a $noun.
lit is a +list.
Produces
a +list.
Source
++ join
|* [sep=* lit=(list)]
=. sep `_?>(?=(^ lit) i.lit)`sep
?~ lit ~
=| out=(list _?>(?=(^ lit) i.lit))
|- ^+ out
?~ t.lit
(flop [i.lit out])
$(out [sep i.lit out], lit t.lit)Examples
> (join ' ' "hoon")
"h o o n"> (join 0 `(list @)`~[1 2 3])
~[1 0 2 0 3]+lent
+lentList length
Produces the length of any +list .a as an atom.
Accepts
.a is a +list.
Produces
an atom.
Source
++ lent
~/ %lent
|= a=(list)
^- @
=+ b=0
|-
?~ a b
$(a t.a, b +(b))Examples
> (lent [1 2 3 4 ~]))
4> (lent [1 'a' 2 'b' (some 10) ~])
5+levy
+levyLogical "and" on list
Computes the Boolean logical "and" on the results of gate .b applied to each individual element in +list .a.
Accepts
.a is a list.
.b is a gate.
Produces
A boolean.
Source
++ levy
~/ %levy
|* [a=(list) b=$-(* ?)]
|- ^- ?
?~ a &
?. (b i.a) |
$(a t.a)Examples
> =a |=(a=@ (lte a 1))
> (levy `(list @)`[0 1 2 1 ~] a)
%.n> =a |=(a=@ (lte a 3))
> (levy `(list @)`[0 1 2 1 ~] a)
%.y+lien
+lienLogical "or" on list
Computes the Boolean logical "or" on the results of applying $gate .b to every element of +list .a.
Accepts
.a is a list.
.b is a gate.
Source
++ lien
~/ %lien
|* [a=(list) b=$-(* ?)]
|- ^- ?
?~ a |
?: (b i.a) &
$(a t.a)Examples
> =a |=(a=@ (gte a 1))
> (lien `(list @)`[0 1 2 1 ~] a)
%.y> =a |=(a=@ (gte a 3))
> (lien `(list @)`[0 1 2 1 ~]) a)
%.n+limo
+limoList Constructor
Turns a null-terminated tuple into a +list.
Accepts
.a is a null-terminated tuple.
Produces
A +list.
Source
++ limo
|* a=*
^+ =< $
|@ ++ $ ?~(a ~ ?:(*? [i=-.a t=$] $(a +.a)))
--
aExamples
> (limo [1 2 3 ~])
[i=1 t=[i=2 t=[i=3 t=~]]]+murn
+murnMaybe transform
Passes each member of +list .a to gate .b, which must produce a +unit. Produces a new list with all the results that do not produce ~.
Accepts
.a is a list.
.b is a gate that produces a unit.
Produces
A list.
Source
++ murn
~/ %murn
|* [a=(list) b=$-(* (unit))]
=> .(a (homo a))
|- ^- (list _?>(?=(^ a) (need (b i.a))))
?~ a ~
=/ c (b i.a)
?~ c $(a t.a)
[+.c $(a t.a)]Examples
> =a |=(a=@ ?.((gte a 2) ~ (some (add a 10))))
> (murn `(list @)`[0 1 2 3 ~] a)
[i=12 t=[i=13 t=~]]+oust
+oustRemove
Removes elements from list .c beginning at inclusive index .a, removing .b number of elements.
Accepts
.c is a list.
Produces
A +list.
Source
++ oust
~/ %oust
|* [[a=@ b=@] c=(list)]
(weld (scag +<-< c) (slag (add +<-< +<->) c))Examples
> (oust [4 5] "good day, urbit!")
"good urbit!"> (oust [2 2] `(list @)`[1 2 3 4 ~])
~[1 2]+reap
+reapReplicate
Replicate: produces a +list containing .a copies of .b.
Accepts
.a is an atom.
.b is a noun.
Produces
A list.
Source
++ reap
~/ %reap
|* [a=@ b=*]
|- ^- (list _b)
?~ a ~
[b $(a (dec a))]Examples
> (reap 20 %a)
~[%a %a %a %a %a %a %a %a %a %a %a %a %a %a %a %a %a %a %a %a]> (reap 5 ~s1)
~[~s1 ~s1 ~s1 ~s1 ~s1]
> `@dr`(roll (reap 5 ~s1) add)
~s5+rear
+rearLast item of list
Produces the last item in list .a, crashing if .a is null.
Accepts
.a is a +list.
Produces
The type of the last element in .a.
Source
++ rear
~/ %rear
|* a=(list)
^- _?>(?=(^ a) i.a)
?> ?=(^ a)
?: =(~ t.a) i.a
$(a t.a)Examples
> (rear ~[1 2 3])
3> (rear ~)
dojo: hoon expression failed+reel
+reelRight fold
Right fold: moves right to left across a +list .a, recursively slamming a binary gate .b with an element from .a and an accumulator, producing the final value of the accumulator.
(To "slam" means to call a gate and give it a sample/samples. In this instance, .a is the list of samples that are given to the gate b.)
The initial value of the accumulator is the bunt of .b's second argument (+<+). This can occasionally produce undesired behavior (see examples). If you need more control over the initial value, try making use of $_ and |:, or perhaps +spin or +spun.
Accepts
.a is a list.
.b is a binary gate.
Produces
The accumulator, which is a noun.
Source
++ reel
~/ %reel
|* [a=(list) b=_=>(~ |=([* *] +<+))]
|- ^+ ,.+<+.b
?~ a
+<+.b
(b i.a $(a t.a))Examples
> (reel `(list @)`[1 2 3 4 5 ~] add)
15
> (reel `(list @)`[6 3 1 ~] sub)
4
> (reel `(list @)`[3 6 1 ~] sub)
! subtract-underflow
! exit+mul's default sample is 1, so calling +reel with +mul yields the expected behavior:
> *mul
1
> (reel `(list @)`~[1 2 3 4] mul)
24However, if you build a gate that uses +mul like so, the sample defaults to 0 since that is the bunt of @:
> (reel `(list @)`~[1 2 3 4] |=([a=@ b=@] (mul a b)))
0We can fix this with |::
> (reel `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))
24If you check the definition of +mul, you'll see that it also utilizes this pattern.
We can check explicitly what sequence of operations +reel performs like this:
> =f |: [l='e_l' r='e_r']
^- @t
:((cury cat 3) '(' l '*' r ')')
> (reel "abcde" f)
'(a*(b*(c*(d*(e*e_r)))))'+roll
+rollLeft fold
Left fold: moves left to right across a list .a, recursively slamming a binary gate .b with an element from the +list and an accumulator, producing the final value of the accumulator.
(To "slam" means to call a gate and give it a sample/samples. In this instance, .a is the list of samples that are given to the gate b.)
The initial value of the accumulator is .b's second argument (+<+). This can occasionally produce undesired behavior (see examples). If you need more control over the initial value, try making use of $_ and |:, or perhaps +spin or +spun.
Accepts
.a is a list.
.b is a binary gate.
Produces
The accumulator, which is a noun.
Source
++ roll
~/ %roll
|* [a=(list) b=_=>(~ |=([* *] +<+))]
|- ^+ ,.+<+.b
?~ a
+<+.b
$(a t.a, b b(+<+ (b i.a +<+.b)))Examples
> (roll `(list @)`[1 2 3 4 5 ~] add)
q=15
> (roll `(list @)`[6 3 1 ~] sub)
! subtract-underflow
! exit
> (roll `(list @)`[1 3 6 ~] sub)
q=4+mul's default sample is 1, so calling +roll with +mul yields the expected behavior:
> *mul
1
> (roll `(list @)`~[1 2 3 4] mul)
24However, if you build a gate that uses +mul like so, the sample defaults to 0 since that is the bunt of @:
> (roll `(list @)`~[1 2 3 4] |=([a=@ b=@] (mul a b)))
0We can fix this with |::
> (roll `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))
24If you check the definition of +mul, you'll see that it also utilizes this pattern.
We can check explicitly what sequence of operations +roll performs like this:
> =f |: [l='e_l' r='e_r']
^- @t
:((cury cat 3) '(' l '*' r ')')
> (roll "abcde" f)
'(e*(d*(c*(b*(a*e_r)))))This is in contrast to what one might expect:
> =foldl
|* [l=(list) f=$-([* *] *)]
^- f
?~ l +<-.f
%= $
+<-.f (f +<-.f i.l)
l t.l
==
> (foldl "abcde" f)
'(((((e_l*a)*b)*c)*d)*e)'+scag
+scagPrefix
Accepts an atom .a and +list .b, producing the first .a elements of the front of the list.
Accepts
.a is an atom.
.b is a list.
Produces
A list of the same type as .b.
Source
++ scag
~/ %scag
|* [a=@ b=(list)]
|- ^+ b
?: |(?=(~ b) =(0 a)) ~
[i.b $(b t.b, a (dec a))]Examples
> (scag 2 `(list @)`[1 2 3 4 ~])
[i=1 t=~[2]]> (scag 10 `(list @)`[1 2 3 4 ~])
[i=1 t=~[2 3 4]]+skid
+skidSeparate
Separates a +list .a into two lists - Those elements of .a who produce true when slammed to gate .b and those who produce %.n.
(To "slam" means to call a gate and give it a sample/samples. In this instance, .a is the list of samples that are given to the gate .b.)
Accepts
.a is a list.
.b is a gate that accepts one argument and produces a flag.
Produces
A cell of two lists.
Source
++ skid
~/ %skid
|* [a=(list) b=$-(* ?)]
|- ^+ [p=a q=a]
?~ a [~ ~]
=+ c=$(a t.a)
?:((b i.a) [[i.a p.c] q.c] [p.c [i.a q.c]])Examples
> =a |=(a=@ (gth a 1))
> (skid `(list @)`[0 1 2 3 ~] a)
[p=[i=2 t=~[3]] q=[i=0 t=~[1]]]+skim
+skimFilter
Cycles through the members of a list .a, passing them to a gate .b and producing a list of all of the members that produce %.y. Inverse of +skip.
Accepts
.a is a list.
.b is a gate that accepts one argument and produces a boolean.
Produces
A list.
Source
++ skim
~/ %skim
|* [a=(list) b=$-(* ?)]
|-
^+ a
?~ a ~
?:((b i.a) [i.a $(a t.a)] $(a t.a))Examples
> =a |=(a=@ (gth a 1))
> (skim `(list @)`[0 1 2 3 ~] a)
[i=2 t=~[3]]+skip
+skipExcept
Cycles through the members of +list .a, passing them to a gate .b. Produces a list of all of the members that produce %.n. Inverse of +skim.
Accepts
.a is a list.
.b is a gate that accepts one argument and produces a flag.
Produces
A list of the same type as .a.
Source
++ skip
~/ %skip
|* [a=(list) b=$-(* ?)]
|-
^+ a
?~ a ~
?:((b i.a) $(a t.a) [i.a $(a t.a)])Examples
> =a |=(a=@ (gth a 1))
> (skip `(l)`[0 1 2 3 ~]) a)
[i=0 t=[i=1 t=~]]+slag
+slagSuffix
Accepts an atom .a and list .b, producing the remaining elements from .b starting at .a.
Accepts
.a is an atom.
.b is a list.
Produces
A list of the same type as .b.
Source
++ slag
~/ %slag
|* [a=@ b=(list)]
|- ^+ b
?: =(0 a) b
?~ b ~
$(b t.b, a (dec a))Examples
> (slag 2 (limo [1 2 3 4 ~]))
[i=3 t=[i=4 t=~]]
> (slag 1 (limo [1 2 3 4 ~]))
[i=2 t=[i=3 t=[i=4 t=~]]]+snag
+snagIndex
Accepts an atom .a and a +list .b, producing the element at the index of .aand failing if the list is null. Lists are 0-indexed.
Accepts
.a is an atom.
.b is a list.
Produces
Produces an element of .b, or crashes if no element exists at that index.
Source
++ snag
~/ %snag
|* [a=@ b=(list)]
|- ^+ ?>(?=(^ b) i.b)
?~ b
~_ leaf+"snag-fail"
!!
?: =(0 a) i.b
$(b t.b, a (dec a))Examples
> (snag 2 "asdf")
'd'> (snag 0 `(list @ud)`~[1 2 3 4])
1+snap
+snapReplace item at index
Accepts a +list .a, an atom .b, and a noun .c, producing the list of .a with the item at index .b replaced with .c.
Accepts
.a is a list.
.b is a atom.
.c is a noun.
Produces
the list of .a with the item at index .b replaced with .c.
Source
++ snap
~/ %snap
|* [a=(list) b=@ c=*]
^+ a
(weld (scag b a) [c (slag +(b) a)])Examples
> (snap (limo ~[2 3 4]) 1 11)
~[2 11 4]+snip
+snipDrop tail off list
Removes the last element from list .a.
Accepts
.a is a +list.
Produces
A +list.
Source
++ snip
~/ %snip
|* a=(list)
^+ a
?~ a ~
?: =(~ t.a) ~
[i.a $(a t.a)]Examples
> `tape`(snip "foobar")
"fooba"> (snip ~)
~+snoc
+snocAppend
Accepts a +list .a and a noun .b, producing the list of .b appended to .a.
Accepts
.a is a list.
.b is a noun.
Produces
Produces a list of .b appended to .a.
Source
++ snoc
|* [a=(list) b=*]
(weld a ^+(a [b]~))Examples
> `tape`(zing (snoc `(list tape)`~["a" "bc" "def"] "g"))
"abcdefg"
> (snoc `(list @ud)`~[1 2 3] 4)
~[1 2 3 4]+sort
+sortQuicksort
Quicksort: accepts a +list .a and a gate .b which accepts two nouns and produces a flag. +sort then produces a list of the elements of .a, sorted according to .b.
Accepts
.a is a list.
.b is a gate that accepts two nouns and produces a boolean.
Produces
A list
Source
++ sort !.
~/ %sort
|* [a=(list) b=$-([* *] ?)]
=> .(a ^.(homo a))
|- ^+ a
?~ a ~
=+ s=(skid t.a |:(c=i.a (b c i.a)))
%+ weld
$(a p.s)
^+ t.a
[i.a $(a q.s)]Examples
> (sort `(list @)`[0 1 2 3 ~] gth)
~[3 2 1 0]+spin
+spinGate to list, with state
Accepts a +list .a, some state .b, and a gate .c. .c is called with a tuple -- the head is an element of .a and the tail is the state .b, and should produce a tuple of the transformed element and the (potentially modified) state .b. Produces a pair where the first element is a list of the transformed elements of .a, and the second element is the final value of .b.
Accepts
.a is a +list.
.b is a noun.
.c is a gate.
Produces
A pair of a list and a noun.
Source
++ spin
~/ %spin
|* [a=(list) b=* c=_|=(^ [** +<+])]
=> .(c `$-([_?>(?=(^ a) i.a) _b] [_-:(c) _b])`c)
=/ acc=(list _-:(c)) ~
|- ^- (pair _acc _b)
?~ a
[(flop acc) b]
=^ res b (c i.a b)
$(acc [res acc], a t.a)Examples
> %^ spin (limo ~[4 5 6]) :: Trivial example -- does nothing with the state
0
|=([n=@ a=@] [n a])
[p=~[4 5 6] q=0]> %^ spin (limo ~[4 5 6]) :: Form a pair with `p` as the index and `q` as the list element
0
|=([n=@ a=@] [`(pair)`[a n] +(a)])
[p=~[[p=0 q=4] [p=1 q=5] [p=2 q=6]] q=3]> %^ spin (reap 10 0) :: Create 10 random numbers less than `10`
~(. og eny)
|=([n=@ rng=_og] (rads:rng 10))
[p=~[7 8 6 0 1 5 4 7 9 3] q=<4.rvi {a/@uvJ <51.qyl 129.pdd 41.mac 1.ane $141>}>]Discussion
(~(rads og eny) 2) creates a random number less than 2, seeding the RNG with entropy (eny). The head of the product is the random number, the tail is the continuation of the RNG.
+spun
+spunGate to list, with state
Accepts a +list .a and a gate .b. .c is internal state, initially derived by bunting the tail of the sample of gate .b, instead of being passed in explicitly as in +spin. Produces a list with the gate applied to each element of the original list. .b is called with a tuple -- the head is an element of .a and the tail is the state .c, and should produce a tuple of the transformed element and the (potentially modified) state .c.
Accepts
.a is a +list.
.b is a gate.
Produces
A list.
Source
++ spun
~/ %spun
|* [a=(list) b=_|=(^ [** +<+])]
p:(spin a +<+.b b)Examples
> %+ spun (limo ~[4 5 6]) :: `p` as the index and `q` as the list element
|=([n=@ a=@] [`(pair)`[a n] +(a)])
~[[p=0 q=4] [p=1 q=5] [p=2 q=6]]> =l (limo ~[7 8 9])
> %+ spun (limo ~[4 5 6]) :: joins two lists into a list of pairs
|=([n=@ a=@] [`(pair)`[(snag a l) n] +(a)])
~[[p=7 q=4] [p=8 q=5] [p=9 q=6]]+swag
+swagInfix
Similar to substr in Javascript: extracts a string infix, beginning at inclusive index .a, producing .b number of characters.
Accepts
.a is an atom.
.b is an atom.
.c is a list.
Produces
A list of the same type as .c.
Source
++ swag
|* [[a=@ b=@] c=(list)]
(scag +<-> (slag +<-< c))Examples
> (swag [2 5] "roly poly")
"ly po"> (swag [2 2] (limo [1 2 3 4 ~]))
[i=3 t=[i=4 t=~]]+turn
+turnGate to list
Accepts a +list .a and a gate .b. Produces a list with the gate applied to each element of the original list.
Accepts
.a is a list.
.b is a gate.
Produces
A list.
Source
++ turn
~/ %turn
|* [a=(list) b=gate]
=> .(a (homo a))
^- (list _?>(?=(^ a) (b i.a)))
|-
?~ a ~
[i=(b i.a) t=$(a t.a)]Examples
> (turn (limo [104 111 111 110 ~]) @t)
<|h o o n|>> =a |=(a=@ (add a 4))
> (turn (limo [1 2 3 4 ~]) a)
~[5 6 7 8]Discussion
+turn is Hoon's version of 'map' in Haskell.
+weld
+weldConcatenate
Concatenate two +lists .a and .b.
Accepts
.a and .b are lists.
Source
++ weld
~/ %weld
|* [a=(list) b=(list)]
=> .(a ^.(homo a), b ^.(homo b))
|- ^+ b
?~ a b
[i.a $(a t.a)]Examples
> (weld "urb" "it")
"urbit"> (weld (limo [1 2 ~]) (limo [3 4 ~]))
~[1 2 3 4]+welp
+welpPerfect weld
Concatenate two +lists a and b without losing their type information to homogenization.
Accepts
a is a list.
b is a list.
Produces
A list.
Source
++ welp
~/ %welp
=| [* *]
|@
++ $
?~ +<-
+<-(. +<+)
+<-(+ $(+<- +<->))
--Examples
> (welp "foo" "bar")
"foobar"> (welp ~[60 61 62] ~[%a %b %c])
[60 61 62 %a %b %c ~]
> ? (welp ~[60 61 62] ~[%a %b %c])
[@ud @ud @ud %a %b %c %~]
[60 61 62 %a %b %c ~]> (welp [sa+1 so+2 ~] si=3)
[[%sa 1] [%so 2] si=3]+zing
+zingTurns a +list of lists into a single list by promoting the elements of each sublist into the higher.
Accepts
A list of lists.
Produces
A list.
Source
++ zing
~/ %zing
=| *
|@
++ $
?~ +<
+<
(welp +<- $(+< +<+))
--Examples
> (zing (limo [(limo ['a' 'b' 'c' ~]) (limo ['e' 'f' 'g' ~]) (limo ['h' 'i' 'j' ~]) ~]))
~['a' 'b' 'c' 'e' 'f' 'g' 'h' 'i' 'j']> (zing (limo [(limo [1 'a' 2 'b' ~]) (limo [3 'c' 4 'd' ~]) ~]))
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