mirror of
https://github.com/ilyakooo0/urbit.git
synced 2024-12-22 22:31:30 +03:00
422 lines
13 KiB
Markdown
422 lines
13 KiB
Markdown
---
|
|
logo: black
|
|
sort: 1
|
|
next: true
|
|
title: Basic Hoon
|
|
---
|
|
|
|
# Basic Hoon
|
|
|
|
Our goal is to get you programming interesting and useful things
|
|
as soon as possible. To get there we have to quickly cover some
|
|
of the fundamentals of hoon. To do this we'll walk through two
|
|
simple programs: the first [Project
|
|
Euler](https://projecteuler.net/) problem and
|
|
[fizzbuzz](https://en.wikipedia.org/wiki/Fizz_buzz).
|
|
|
|
To run this code, you'll need an urbit, and you'll need the
|
|
`%examples` desk from `~wactex-ribmex`. If you haven't installed
|
|
urbit yet, check out the [installation
|
|
instructions](http://urbit.org/docs/user/install). Once urbit is
|
|
intalled, take a look at the [basic
|
|
operation](http://urbit.org/docs/user/basic) of your urbit.
|
|
|
|
If you haven't pulled the examples desk from `~wactex-ribmex`, do
|
|
so now:
|
|
|
|
~fintud-macrep:dojo> |merge %examples ~wactex-ribmex %examples
|
|
>=
|
|
; ~wactex-ribmex is your neighbor
|
|
; ~wactex-ribmex is your neighbor
|
|
[time passes...]
|
|
merged with strategy %init
|
|
|
|
The merge could take several minutes; you'll know it's done when
|
|
"merged with strategy %init" is printed. Mount the new files to
|
|
your Unix pier directory:
|
|
|
|
~fintud-macrep:dojo> |mount /=examples=
|
|
|
|
Switch desks to run commands from the `%examples` desk:
|
|
|
|
~fintud-macrep:dojo> =dir /=examples=
|
|
=% /~fintud-macrep/examples/~2015.11.13..02.25.00..41e9/
|
|
|
|
Run an example:
|
|
|
|
~fintud-macrep:dojo> +euler1
|
|
233.168
|
|
|
|
## Euler 1
|
|
|
|
Let's check out the code for Euler 1. First, the problem:
|
|
|
|
```
|
|
If we list all the natural numbers below 10 that are multiples of
|
|
3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
|
|
|
|
Find the sum of all the multiples of 3 or 5 below 1000.
|
|
```
|
|
|
|
Here is the hoon solution (which should be in your pier directory
|
|
under `/examples/gen/euler1.hoon`):
|
|
|
|
```
|
|
:: project euler 1
|
|
:: https://projecteuler.net/problem=1
|
|
:: run in dojo with +euler1
|
|
::
|
|
:::: /hoon/euler1/gen
|
|
::
|
|
:- %say |= *
|
|
:- %noun
|
|
=< (sum 1.000)
|
|
::
|
|
:::: ~fintud-macrep
|
|
::
|
|
|%
|
|
++ three
|
|
|= a=@
|
|
=| b=@
|
|
|- ^- @u
|
|
?: (lth a b)
|
|
0
|
|
(add b $(b (add 3 b)))
|
|
|
|
++ five
|
|
|= a=@
|
|
=| b=@
|
|
|- ^- @
|
|
?: (lte a b)
|
|
0
|
|
?: =((mod b 3) 0)
|
|
$(b (add b 5))
|
|
(add b $(b (add b 5)))
|
|
|
|
++ sum
|
|
|= a=@u
|
|
(add (five a) (three a))
|
|
--
|
|
```
|
|
|
|
> Hoon is not generally whitespace sensitive, but we do have two
|
|
> different kinds of whitespace: a single space and a gap, which
|
|
> is two or more spaces or a linebreak. Tabs are taboo. Do not
|
|
> use them. Really. For a more detailed explanation of when to
|
|
> use spaces vs. gaps, see the syntax section before the first
|
|
> excercises.
|
|
|
|
### Lines 1-11:
|
|
|
|
Any line that begins with `::` is a comment.
|
|
|
|
:- %say |= *
|
|
:- %noun
|
|
=< (sum 1.000)
|
|
|
|
All you need to know about the lines above is that they call the
|
|
`++sum` function with an argument of `1.000`. We'll cover them in
|
|
more detail later.
|
|
|
|
### How to form expressions
|
|
|
|
Hoon does not use reserved words to form expressions. Instead,
|
|
expressions are formed with runes, which are diagraphs of two
|
|
ascii symbols. Each rune takes a specific number of
|
|
children--either expressions formed by other runes or literals
|
|
that produce their own value.
|
|
|
|
For example, the rune `?:` from line 17 is the classic
|
|
'if-then-else' statement, and thus takes three children:
|
|
|
|
?: (lth a b) :: if first child evals to true
|
|
0 :: then produce result of second
|
|
(add b $(b (add 3 b))) :: else, produce result of third
|
|
|
|
Since runes are such a fundamental structure in Hoon, we found
|
|
ourselves speaking them out loud frequently. It quickly grew
|
|
cumbersome to have to say "question mark, colon" to describe
|
|
`?:`. To alleviate this problem, we came up with our own naming
|
|
scheme: each ascii glyph has a single syllable pronunciation
|
|
phonetically designed to be both easily remembered and easily
|
|
pronounced in conjunction with the other glyphs (when forming a
|
|
rune).
|
|
|
|
See the entire naming schema below/or link to it:
|
|
|
|
```
|
|
ace [1 space] gal < pel (
|
|
bar | gap [>1 space, nl] per )
|
|
bas \ gar > sel [
|
|
buc $ hax # sem ;
|
|
cab _ hep - ser ]
|
|
cen % kel { soq '
|
|
col : ker } tar *
|
|
com , ket ^ tec `
|
|
doq " lus + tis =
|
|
dot . pam & wut ?
|
|
fas / pat @ zap !
|
|
```
|
|
|
|
Using our naming scheme `?:` is said 'wut col'.
|
|
|
|
### Lines 12-34
|
|
|
|
Now let's quickly walk through this code line-by-line. Lines
|
|
12-34 are wrapped in a `|%` (pronounced 'bar cen'), which
|
|
produces a core, a fundamental datatype in hoon similar to a
|
|
struct, class, or object. A core is just a map of names
|
|
to any kind of code, whether it be functions or data. Each
|
|
element in this map begins with a `++` followed by the name and
|
|
the corresponding code. Since `|%` takes an arbitrary number of
|
|
children, it needs to be closed with a `--`.
|
|
|
|
> `++` is not technically a rune, since it is only used in core
|
|
> syntax as shown above
|
|
|
|
Let's step into each of the three arms within our core.
|
|
|
|
### `++ sum`
|
|
|
|
++ sum
|
|
|= a=@
|
|
(add (five a) (three a))
|
|
--
|
|
|
|
`|=` produces a function, much like a lambda in lisp. It takes two children:
|
|
|
|
- A set of argument(s). In this case our argument set only
|
|
contains one: `a` which is required to be an atom or natural
|
|
number, denoted by `@`.
|
|
|
|
- The body of the function itself, which is executed when the
|
|
function is called (in this case, with `(sum 1.000)`). This
|
|
particular function adds the results of evaluating the gates `++
|
|
five` and `++three` with each of their respective input
|
|
parameters set to `a`.
|
|
|
|
### ++ three
|
|
|
|
++ three
|
|
|= a=@
|
|
=| b=@
|
|
|- ^- @u
|
|
?: (lth a b)
|
|
0
|
|
(add b $(b (add 3 b)))
|
|
|
|
As above, `++three` takes an integer argument, `a`, and then
|
|
executes the remainder of the code with `a` set to the actual
|
|
arguments.
|
|
|
|
Similarly, `=|` pushes its first child, `b` into our context (in
|
|
other words, it declares a variable `b`) and executes the
|
|
remainder of the code. However, `b` is not an argument; `=|`
|
|
sets `b` to the default value of whatever type it is declared as.
|
|
Since the default value of an atom is `0`, b is set to `0`.
|
|
|
|
So now we have two variables: `a` is set to our input, and `b` is
|
|
initialized to `0`.
|
|
|
|
The easiest way to think about `|-` that it lays down a recursion
|
|
point. More on this later.
|
|
|
|
`^-` is just a cast that sets the result of the remainder of the
|
|
code to an unsigned integer, `@u`.
|
|
|
|
In pseudocode, the last three lines read like this: if `a` is
|
|
less than `b`, produce zero. Else, add `b` to the result of
|
|
rerunning the segment of the function following the `|-` with the
|
|
value of `b` changed to `b` plus three.
|
|
|
|
The only thing that should look completely unfamiliar to you here
|
|
is the `$(b (add 3 b))`, which causes us to recurse back to our
|
|
last recursion point with the value of `b` set to `(add 3 b)`.
|
|
Note that we only specify what changes (`b` in this case). If
|
|
you recurse by an actual function call, then you have to specify
|
|
every argument.
|
|
|
|
> If you're familiar with Clojure, `|-` is `loop` and `$()` is
|
|
> recur.
|
|
|
|
|
|
## Excercises
|
|
|
|
Please tweak your code to complete the following excercises.
|
|
|
|
There are a few runes and some syntax that we have yet to cover that
|
|
you will need to complete the excercises below. For these, please
|
|
refer to our cheatsheat at the bottom.
|
|
|
|
1. Read and understand `++five` line by line.
|
|
|
|
2. Change `++sum` to accept two variables, `a` and `b`. Pass `a`
|
|
to three and `b` to five. Then run the code with `a` set to
|
|
`1.000` and b set to `2.000`.
|
|
|
|
3. Check if this new result is under one thousand. If it is,
|
|
return the string 'result is less than one thousand'. If not,
|
|
return 'result is greater than or equal to one thousand'.
|
|
|
|
```
|
|
Review
|
|
|
|
|% start core (collection of named ++ arms)
|
|
|= define function
|
|
=| define variable from type with default value
|
|
|- drop a recursion point
|
|
^- cast
|
|
?: if-then-else
|
|
=(a b) test equality
|
|
(function args ...) call function
|
|
|
|
New material
|
|
|
|
- :- make a cell of values. The irregular wide form of this is
|
|
[a b] with two expressions separated by a single space.
|
|
|
|
- Cords are one datatype for text in hoon. They're just a big
|
|
atom formed from adjacent unicode bytes -- a "c string". To
|
|
produce a cord enclose text within single quotes. To set the type
|
|
of an argument to a cord, use @t.
|
|
|
|
- There are two syntaxes for writing Hoon: tall form and wide
|
|
form.
|
|
|
|
In tall form, expressions are formed with either two spaces or
|
|
a line break separating both a rune from its children and each
|
|
of its children from one another. We use tall form when writing
|
|
multiline expressions.
|
|
|
|
For more concise expressions, we use wideform, which is always
|
|
a single line. Wideform can be used inside tall form
|
|
expressions, but not vice versa.
|
|
|
|
Wideform expressions are formed with a rune followed by ()
|
|
containing its children, all of which are separated by a
|
|
single space. For example to make a cell of two elements:
|
|
|
|
:-(a b)
|
|
|
|
We've already seen wideform in action, for example with
|
|
=((mod b 3) 0). In this case = is actually an irregular form
|
|
of .=, which tests its two children for equality.
|
|
|
|
Another irregular form is [a b] for :-(a b)
|
|
|
|
Surrounding a function with () is an irregular wide form
|
|
syntax for calling a function with n arguments.
|
|
```
|
|
|
|
|
|
## The subject
|
|
|
|
Now we're going to cover the boiler plate that we skimmed over
|
|
earlier.
|
|
|
|
:- %say |= *
|
|
:- %noun
|
|
=< (sum [1.000 2.000])
|
|
|
|
This program is a cell of two elements: the first, `%say`, tells
|
|
the interpreter what to produce--in this case a value.
|
|
|
|
The second element is `|=`, which we know produces a function.
|
|
`|=`'s first child is its argument(s), which in this case is any
|
|
noun (`*`). Its second child is the remainder of the program.
|
|
|
|
Similarly, the rest of the program is a cell of the literal
|
|
`%noun`, which tells the shell that we're producing a value of
|
|
type `noun`, and the second child contains the code that we run
|
|
to actually produce our value of the type `noun`.
|
|
|
|
`=<` is a rune that takes two children. The second child is the
|
|
context against which we run the first child. So in this case, we
|
|
are running the expression `(sum 1.000)` against everything
|
|
contained within the `|%`. In Hoon, we call the code executed the
|
|
"formula" and its context the "subject".
|
|
|
|
```
|
|
::::::::::::::::::::::::::::::
|
|
=< (sum 1.000) :: formula
|
|
::::::::::::::::::::::::::::::
|
|
|% ::
|
|
++ three ::
|
|
|= a=@ ::
|
|
=| b=@ ::
|
|
|- ^- @u ::
|
|
?: (lth a b) ::
|
|
0 ::
|
|
(add b $(b (add 3 b))) ::
|
|
::
|
|
++ five ::
|
|
|= a=@ :: subject
|
|
=| b=@ ::
|
|
|- ^- @ ::
|
|
?: (lte a b) ::
|
|
0 ::
|
|
?: =((mod b 3) 0) ::
|
|
$(b (add b 5)) ::
|
|
(add b $(b (add b 5))) ::
|
|
::
|
|
++ sum ::
|
|
|= a=@u ::
|
|
(add (five a) (three a)) ::
|
|
-- ::
|
|
::::::::::::::::::::::::::::::
|
|
```
|
|
|
|
In nearly every language there is a similar concept of a
|
|
"context" in which expressions are executed. For example, in C
|
|
this includes things like the call stack, stack variables, and so
|
|
on.
|
|
|
|
Hoon is unique in that this context is a first-class value.
|
|
Scheme allows a sort of reification of the context through
|
|
continutations, and some may see a parallel to Forth's stack, but
|
|
Hoon takes takes the concept one step further.
|
|
|
|
Our starting subject is the standard library, which is defined in
|
|
`/arvo/hoon.hoon` and `/arvo/zuse.hoon`. This is where functions
|
|
like `add` are defined. When we define a core with `|%`, we
|
|
don't throw away the subject (i.e. the standard library); rather,
|
|
we stack the new core on top of the old subject so that both are
|
|
accessible.
|
|
|
|
## Exercises:
|
|
|
|
4. Pass `++sum` its arguments (`2000` and `3000`) from the
|
|
commandline.
|
|
|
|
5. Comment out all of the arms of the `|%`. Now add another arm
|
|
and call it `++add`, have it accept two arguments and procduce
|
|
42 (regardless of input). Change the `=<` line to `[(add 5 7)
|
|
(^add 5 7)]`. Can you recognize what's happening?
|
|
|
|
6. Write fizbuzz:
|
|
|
|
Write a program that prints the numbers from 1 to 100
|
|
(entered from the command line). But for multiples of three
|
|
print 'Fizz' instead of the number and for the multiples of
|
|
five print 'Buzz'. For numbers which are multiples of both
|
|
three and five print 'FizzBuzz'.
|
|
|
|
Cheatsheet:
|
|
|
|
- To pass arguments from the command line to a program, you
|
|
replace the `*` in the first line of the boiler plate to
|
|
`[^ [[arg=TYPE ~] ~]]` where `TYPE` is replaced with the
|
|
type of argument you're expecting. Then `+euler1 a` from
|
|
the dojo sets `arg` to `a`.
|
|
- A list of strings is of type `(list ,@t)`, so the result of
|
|
the fizzbuzz function is of this type (hint: you'll need to
|
|
use `^-`)
|
|
- The empty list is `~`
|
|
- Lisp-style cons (construct a cell/prepend an element) is
|
|
`[new-element list]`
|
|
- For example, the first three positive integers are `[1 2 3
|
|
~]`
|
|
- `gte` tests whether `a` is greater than or equal to `b`.
|
|
- `mod` runs the modulo operation on two atoms.
|
|
- See the [basic math section]() for more info.
|