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                                                    • 1a: Basic Arithmetic
                                                    • 1b: Tree Addressing
                                                    • 1c: Molds and Mold-Builders
                                                    • 2a: Unit Logic
                                                    • 2b: List Logic
                                                    • 2c: Bit Arithmetic
                                                    • 2d: Bit Logic
                                                    • 2e: Insecure Hashing
                                                    • 2f: Noun Ordering
                                                    • 2g: Unsigned Powers
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                                                    • 2l: Container from Container
                                                    • 2m: Container from Noun
                                                    • 2n: Functional Hacks
                                                    • 2o: Normalizing Containers
                                                    • 2p: Serialization
                                                    • 2q: Molds and Mold-Builders
                                                    • 3a: Modular and Signed Ints
                                                    • 3b: Floating Point
                                                    • 3c: Urbit Time
                                                    • 3d: SHA Hash Family
                                                    • 3e: AES encryption (Removed)
                                                    • 3f: Scrambling
                                                    • 3g: Molds and Mold-Builders
                                                    • 4a: Exotic Bases
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                                                    • 4f: Parsing (Rule-Builders)
                                                    • 4g: Parsing (Outside Caller)
                                                    • 4h: Parsing (ASCII Glyphs)
                                                    • 4i: Parsing (Useful Idioms)
                                                    • 4j: Parsing (Bases and Base Digits)
                                                    • 4k: Atom Printing
                                                    • 4l: Atom Parsing
                                                    • 4m: Formatting Functions
                                                    • 4n: Virtualization
                                                    • 4o: Molds
                                                    • 5a: Compiler Utilities
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                                                    • 5c: Compiler Backend & Prettyprinter
                                                    • 5d: Parser
                                                    • 5e: Molds and mold builders
                                                    • 5f: Profiling support
                                                    • Runes

                                                      • Constants (Atoms and Strings)
                                                      • + lus · Arms
                                                      • | bar · Cores
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                                                      • ~ sig · Hints
                                                      • = tis · Subject
                                                      • ? wut · Conditionals
                                                      • ! zap · Wild
                                                      • --, == Terminators
                                                      • Limbs and wings

                                                        • Limbs
                                                        • Wings
                                                        • Zuse

                                                          • 2d(1-5): To JSON, Wains
                                                          • 2d(6): From JSON
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                                                                                              Reference/Hoon/Runes

                                                                                              ^ ket · Casts

                                                                                              ^- ("kethep"), ^+ ("ketlus"), and ^= ("kettis") let us adjust types without violating type constraints.

                                                                                              The nest algorithm which tests subtyping is conservative; it never allows invalid nests, it sometimes rejects valid nests.

                                                                                              ^| "ketbar"

                                                                                              Convert a gold core to an iron core (contravariant).

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^| p
                                                                                              Wide
                                                                                              ^|(p)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktbr p=hoon]

                                                                                              Produces

                                                                                              p as an iron core; crash if not a gold core.

                                                                                              Discussion

                                                                                              An iron core is an opaque function (gate or door).

                                                                                              Theorem: if type x nests within type a, and type y nests within type b, a core accepting b and producing x nests within a iron core accepting y and producing a.

                                                                                              Informally, a function fits an interface if the function has a more specific result and/or a less specific argument than the interface.

                                                                                              Examples

                                                                                              The prettyprinter shows the core metal (. gold, | iron):

                                                                                              ~zod:dojo> |=(@ 1)
                                                                                              <1.gcq [@ @n <250.yur 41.wda 374.hzt 100.kzl 1.ypj %151>]>
                                                                                              ~zod:dojo> ^|(|=(@ 1))
                                                                                              <1|gcq [@ @n <250.yur 41.wda 374.hzt 100.kzl 1.ypj %151>]>

                                                                                              ^: "ketcol"

                                                                                              Mold gate for type p.

                                                                                              Note this rune is now redundant.

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^: p
                                                                                              Wide
                                                                                              ^:(p)
                                                                                              Irregular
                                                                                              ,p

                                                                                              AST

                                                                                              [%ktcl p=spec]

                                                                                              Produces

                                                                                              A gate that returns the sample value if it's of the correct type, but crashes otherwise.

                                                                                              Discussion

                                                                                              ^: is used to produce a mold that crashes if its sample is of the wrong type.

                                                                                              Molds used to produced their bunt value if they couldn't mold their sample. This is no longer the case: molds now crash if molding fails, so this rune is redundant.

                                                                                              One may expect that ^:(path /foo) would result in a syntax error since ^: only takes one child, but instead it will parse as =< ^ %:(path /foo). Since : is the irregular syntax for =< this is is parsed as "get ^ (i.e. the mold for cells) from a subject of (path /foo)", with : being the irregular syntax for =<.

                                                                                              Examples

                                                                                              > ^: @
                                                                                              < 1.goa
                                                                                              { *
                                                                                              {our/@p now/@da eny/@uvJ}
                                                                                              <19.hqf 23.byz 5.mzd 36.apb 119.zmz 238.ipu 51.mcd 93.glm 74.dbd 1.qct $141>
                                                                                              }
                                                                                              >
                                                                                              > (^:(@) 22)
                                                                                              22
                                                                                              > (^:(@) [22 33])
                                                                                              ford: %ride failed to execute:

                                                                                              ^. "ketdot"

                                                                                              Typecast on value produced by passing q to p.

                                                                                              Syntax

                                                                                              Two arguments, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^. p
                                                                                              q
                                                                                              Wide
                                                                                              ^.(p q)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktdt p=hoon q=hoon]

                                                                                              Expands to

                                                                                              ^+(%:(p q) q)

                                                                                              Discussion

                                                                                              p produces a gate and q is any Hoon expression.

                                                                                              ^. is particularly useful when p is a gate that 'cleans up' the type information about some piece of data. For example, limo is used to turn a raw noun of the appropriate shape into a genuine list. Hence we can use ^. to cast with limo and similar gates, ensuring that the product has the desired type.

                                                                                              Examples

                                                                                              > =mylist [11 22 33 ~]
                                                                                              > ?~(mylist ~ i.mylist)
                                                                                              mint-vain
                                                                                              > =mylist ^.(limo mylist)
                                                                                              > ?~(mylist ~ i.mylist)
                                                                                              11
                                                                                              > ?~(mylist ~ t.mylist)
                                                                                              ~[22 33]

                                                                                              ^- "kethep"

                                                                                              Typecast by explicit type label.

                                                                                              Syntax

                                                                                              Two arguments, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^- p
                                                                                              q
                                                                                              Wide
                                                                                              ^-(p q)
                                                                                              Irregular
                                                                                              `p`q

                                                                                              AST

                                                                                              [%kthp p=spec q=hoon]

                                                                                              Expands to

                                                                                              ^+(^*(p) q)

                                                                                              Discussion

                                                                                              It's a good practice to put a ^- ("kethep") at the top of every arm (including gates, loops, etc). This cast is strictly necessary only in the presence of head recursion (otherwise you'll get a rest-loop error, or if you really screw up spectacularly an infinite loop in the compiler).

                                                                                              Examples

                                                                                              ~zod:dojo> (add 90 7)
                                                                                              97
                                                                                              ~zod:dojo> `@t`(add 90 7)
                                                                                              'a'
                                                                                              ~zod:dojo> ^-(@t (add 90 7))
                                                                                              'a'
                                                                                              /~zod:dojo> =foo |= [email protected]
                                                                                              ^- (unit @ta)
                                                                                              `a
                                                                                              /~zod:dojo> (foo 97)
                                                                                              [~ ~.a]

                                                                                              ^+ "ketlus"

                                                                                              Typecast by inferred type.

                                                                                              Syntax

                                                                                              Two arguments, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^+ p
                                                                                              q
                                                                                              Wide
                                                                                              ^+(p q)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktls p=hoon q=hoon]

                                                                                              Produces

                                                                                              The value of q with the type of p, if the type of q nests within the type of p. Otherwise, nest-fail.

                                                                                              Examples

                                                                                              ~zod:dojo> ^+('text' %a)
                                                                                              'a'

                                                                                              ^& "ketpam"

                                                                                              Convert a core to a zinc core (covariant).

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^& p
                                                                                              Wide
                                                                                              ^&(p)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktpm p=hoon]

                                                                                              Produces

                                                                                              p as a zinc core; crash if p isn't a gold or zinc core.

                                                                                              Discussion

                                                                                              A zinc core has a read-only sample and an opaque context. See Advanced types.

                                                                                              Examples

                                                                                              The prettyprinter shows the core metal in the arm labels 1.xoz and 1&xoz below (. is gold, & is zinc):

                                                                                              > |=(@ 1)
                                                                                              < 1.xoz
                                                                                              { @
                                                                                              {our/@p now/@da eny/@uvJ}
                                                                                              <19.hqf 23.byz 5.mzd 36.apb 119.zmz 238.ipu 51.mcd 93.glm 74.dbd 1.qct $141>
                                                                                              }
                                                                                              >
                                                                                              > ^&(|=(@ 1))
                                                                                              < 1&xoz
                                                                                              { @
                                                                                              {our/@p now/@da eny/@uvJ}
                                                                                              <19.hqf 23.byz 5.mzd 36.apb 119.zmz 238.ipu 51.mcd 93.glm 74.dbd 1.qct $141>
                                                                                              }
                                                                                              >

                                                                                              You can read from the sample of a zinc core, but not change it:

                                                                                              > =mycore ^&(|=([email protected] 1))
                                                                                              > a.mycore
                                                                                              0
                                                                                              > mycore(a 22)
                                                                                              -tack.a
                                                                                              -find.a
                                                                                              ford: %slim failed:
                                                                                              ford: %ride failed to compute type:

                                                                                              ^~ "ketsig"

                                                                                              Fold constant at compile time.

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^~ p
                                                                                              Wide
                                                                                              ^~(p)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktsg p=hoon]

                                                                                              Produces

                                                                                              p, folded as a constant if possible.

                                                                                              Examples

                                                                                              > (make '|-(42)')
                                                                                              [%8 p=[%1 p=[1 42]] q=[%9 p=2 q=[%0 p=1]]]
                                                                                              > (make '^~(|-(42))')
                                                                                              [%1 p=42]

                                                                                              ^* "kettar"

                                                                                              Produce example type value.

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^* p
                                                                                              Wide
                                                                                              ^*(p)
                                                                                              Irregular
                                                                                              *p

                                                                                              p is any structure expression.

                                                                                              AST

                                                                                              [%kttr p=spec]

                                                                                              Produces

                                                                                              A default value (i.e., 'bunt value') of the type p.

                                                                                              Examples

                                                                                              Regular:

                                                                                              > ^* @
                                                                                              0
                                                                                              > ^* %baz
                                                                                              %baz
                                                                                              > ^* ^
                                                                                              [0 0]
                                                                                              > ^* ?
                                                                                              %.y

                                                                                              Irregular:

                                                                                              > *@
                                                                                              0
                                                                                              > *^
                                                                                              [0 0]
                                                                                              > *tape
                                                                                              ""

                                                                                              ^= "kettis"

                                                                                              Bind name to a value.

                                                                                              Syntax

                                                                                              Two arguments, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^= p
                                                                                              q
                                                                                              Wide
                                                                                              ^=(p q)
                                                                                              Irregular
                                                                                              p=q

                                                                                              AST

                                                                                              [%ktts p=skin q=hoon]

                                                                                              Produces

                                                                                              If p is a term, the product q with type [%face p q]. p may also be a tuple of terms, or a term-skin pair; the type of q must divide evenly into cells to match it.

                                                                                              Examples

                                                                                              > a=1
                                                                                              a=1
                                                                                              > ^= a
                                                                                              1
                                                                                              a=1
                                                                                              > ^=(a 1)
                                                                                              a=1
                                                                                              > [b c d]=[1 2 3 4]
                                                                                              [b=1 c=2 d=[3 4]]
                                                                                              > [b c d=[x y]]=[1 2 3 4]
                                                                                              [b=1 c=2 d=[x=3 y=4]]

                                                                                              ^? "ketwut"

                                                                                              Convert any core to a lead core (bivariant).

                                                                                              Syntax

                                                                                              One argument, fixed.

                                                                                              FormSyntax
                                                                                              Tall
                                                                                              ^? p
                                                                                              Wide
                                                                                              ^?(p)
                                                                                              IrregularNone.

                                                                                              AST

                                                                                              [%ktwt p=hoon]

                                                                                              Produces

                                                                                              p as a lead core; crash if not a core.

                                                                                              Discussion

                                                                                              A lead core is an opaque generator; the payload can't be read or written.

                                                                                              Theorem: if type x nests within type a, a lead core producing x nests within a lead core producing a.

                                                                                              Informally, a more specific generator can be used as a less specific generator.

                                                                                              Examples

                                                                                              The prettyprinter shows the core metal (. gold, ? lead):

                                                                                              > |=(@ 1)
                                                                                              <1.gcq [@ @n <250.yur 41.wda 374.hzt 100.kzl 1.ypj %151>]>
                                                                                              > ^?(|=(@ 1))
                                                                                              <1?gcq [@ @n <250.yur 41.wda 374.hzt 100.kzl 1.ypj %151>]>

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                                                                                              Last modified March 17, 2023