3 title/'1c: Molds and Mold-Builders'
9# 1c: molds and mold builders
15Atom representing block size. A block of size `a` has a bitwidth of `2^a`.
26 :: ++met measures how many a-bloqs long an atom is.
46 > (met 5 9.999.999.999)
55You can think of `bloq` as a numeral system that can represent values of
56`a^2^2`, where `a` is the block size. That's because a block of size
57`a` contains `a^2` bits, and a binary number that is `b` bits wide can represent
60A `bloq` of 0 has a bitwidth of 1. (2^0 bits; can represent 2 values.)
62A `bloq` of 1 has a bitwidth of 2. (2^1 bits; can represent 4 values.)
64A `bloq` of 2 has a bitwidth of 4. (2^2 bits; can represent 16 values.)
66A `bloq` of 3 has a bitwidth of 8. (2^3 bits; can represent 256 values.)
70See the [bit arithmetic](../2c) section for operations that use `bloq`s.
76Mold of fork between two types
78A mold generator. Produces a discriminated fork between two types, defaulting to
84 |*([a=mold b=mold] $%([$| p=b] [$& p=a]))
91 ?({$.y p/@t} {$.n p/@da})
95 ?({$.y p/*} {$.n p/""})
104A core with one arm, `$`--the empty name--which transforms a sample noun into a
105product noun. If used dryly as a type, the subject must have a sample type of
120 <1.rdl {* <31.ohr 1.jmk $143>}>
121 <1.rdl {* <31.ohr 1.jmk $143>}>
123 > (`gate`|=(a=* [a 'b']) 1)
126 > (`gate`|=(a=@ [a 'b']) 1)
133A `gate` is analogous to a function in other programming languages. We created
134this new jargon because other constructs in Urbit are "functions" in the
135mathematical sense. Any `gate` normalizes to an iron `gate`.
137See also: [`++lift`](../2a), [`++cork`](../2n)
144A mold generator. Generates a mold of a null-terminated list of a
152 |*(a=mold $@($~ (lest a)))
167 > `(list @)`[1 2 'j' ~]
173See also: [`++turn`](../2b), [`++snag`](../2b)
180A mold generator. Puts face of `p` on the passed-in mold.
212A mold generator. Produces a tuple of two of the types passed in.
219 |*([a=mold b=mold] [p=a q=b])
238A mold generator. A `list` without the faces `i` and `t`.
244 |*(a=mold $@($~ [a (pole a)]))
251 > =/(a "asdf" ?>(?=(^ a) `(lest @tD)`a))
252 [i='a' t=[i='s' t=[i='d' t=[i='f' t=~]]]]
254 > `(pole char)`"asdf"
255 ['a' ['s' ['d' ['f' ~]]]]
264A mold generator. Produces a tuple of four of the types passed in.
270 |* [a=mold b=mold c=mold d=mold]
277 > *(qual date time tape cord)
278 [p=[[a=%.y y=0] m=0 t=[d=0 h=0 m=0 s=0 f=~]] q=~292277024401-.1.1 r="" s='']
280 > *(qual (list @) @u @ud @ux)
287Mold of pair of `list` and type
289A mold generator. Produces a tuple of a `list` of `a` and the mold of `b`.
295 |*([a=mold b=mold] [(list a) b])
304 > `(quip @ @ux)`[[1 2 3 4 ~] 0x10]
310A common pattern in Hoon code is to return a `list` of changes, along with a
311new state. You'll often see `quip` used in Gall apps.
318A trap is a core with one arm `$`.
331 <1?dxy 1.oeg {a/<1|rbb {* <31.ohr 1.jmk $143>}> <31.ohr 1.jmk $143>}>
346A mold generator. A `tree` can be empty, or contain a node of a type and
347left/right sub `tree` of the same type. Pretty-printed with `{}`.
353 |*(a=mold $@($~ [n=a l=(tree a) r=(tree a)]))
359 > `(tree [@ tape])`[[1 "hi"] [[2 "bye"] ~ ~] ~]
369A mold generator. A mold of the tuple of the three types passed in.
375 |*([a=mold b=mold c=mold] [p=a q=b r=c])
384 > *(trel cord bloq tape)
393A mold generator. A `unit` is either `~` or `[~ u=a]`, where `a` is the
394type that was passed in.
401 |*(a=mold $@($~ [$~ u=a]))
421Using a `unit` allows you to specify something that may not be there.
423See also: [`++bind`](../2b)
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